Review of the 21st Century Truck Partnership: Third Report (2015)

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Engine Systems, Aftertreatment, Fuels, Lubricants, and Materials

INTRODUCTION

Heavy-duty truck engines, emissions control technology, and fuels are central to all aspects of the 21st Century Truck Partnership’s (21CTP’s) vision of improved thermal efficiency, reduced oil dependency, low-exhaust emissions, lower cost, and improved safety. Although diesel engines used in new trucks are among the most efficient and clean on-road transportation power plants available today, in the opinion of the committee there are still opportunities for making them better. In some heavy-duty applications, gasoline spark-ignition engines are also used. Despite the fact that they are not as efficient as diesel engines, the lower cost of the engine system (which includes emissions control) and the lower cost of the fuel results in lower ownership and operating expenses relative to diesel power plants for their specific applications. However, spark-ignition engines being developed today are incorporating technologies that make them look more diesel-like (e.g., turbocharged direct-injection engines). Consequently many of the fundamental issues that need to be addressed to facilitate reduced fuel consumption in diesels are also of value for spark-ignition engines, and vice versa (e.g., spray characterization, vaporization and mixing phenomena, autoignition, combustion and emission kinetics, and cost-effective lean-emissions control systems).

This chapter covers the 21CTP programs in diesel engines, fuels and lubricants, aftertreatment systems, high-temperature materials, and health concerns raised by diesel engine emissions. In the mobility domain being addressed within 21CTP, the internal combustion engine and its associated emissions control systems and their fuels represent continuously improving, state-of-the-art transportation technologies, offering the lowest life-cycle costs for near-term propulsion technologies (21CTP, 2013, p. 33).

Commensurate with the evolution of heavy-duty (HD) engine and emissions control technologies during the first 15 years of the 21st century, vehicle fuel and lubricant technology is also changing. Petroleum-based diesel fuel regulations have been updated (e.g., lower sulfur limits) to allow for advanced emissions control components, a variety of biofuels have been developed for the purpose of extending transportation fuel supplies from renewable sources, and synthetic hydrocarbons have been produced from natural gas, recycled plastics, and organic refuse. In addition, new lubricant formulations have provided increased fuel efficiency for light-duty vehicles. Research on development of new fuel-efficient lubricant formulations for heavy-duty vehicles is in progress. It is also important to note that the supply of petroleum-based fuels from within the United States has increased significantly owing to the development of new hydraulic fracturing (“fracking”) and directional drilling techniques.

Nonpetroleum diesel fuels can be produced from renewable resources such as seed oils and animal fat, as well as synthesized from natural gas, biomass, oil sands, coal, and other resources. Cellulosic ethanol production facilities are being brought online using technology developed in part by Department of Energy (DOE) laboratories, although the volumes produced will be small. Facilities for the production of renewable diesel fuel from biomass resources continue to be developed, and the production and sale of biodiesel is growing in the United States at a modest rate.¹ The use of syncrudes from tar sands in Canada has also grown. Fischer-Tropsch (F-T) diesel fuel, synthesized from natural gas, has been studied in conventional diesel engine tests in many laboratories to quantify its beneficial impact on emissions. Natural gas has also been described as a potential replacement for liquid petroleum fuels. This application is discussed in detail in a recent National Research Council (NRC, 2014) report. Future expanded use in medium- and heavy-duty vehicles will depend on lowering the cost of on-board fuel storage, as well as the cost of dispensing facilities. Lubricant properties and composition can have a beneficial effect on

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¹ See Biodiesel Production Statistics at http://www.biodiesel.org/production/production-statistics.

vehicle fuel efficiency by reducing engine and driveline friction. Conversely, some engine oil components can adversely affect vehicle emissions by reducing the durability of exhaust emissions control devices. The sulfur, phosphorus, and ash content of lubricants needs to be minimized to prevent degradation of all types of catalytic devices.

Integral to the industries’ efforts to increase efficiency is the push to operate the engine at higher peak cylinder pressures. As oxides of nitrogen (NO_x) aftertreatment systems continue to improve, there is a tendency for the industry to also push the in-cylinder temperatures higher because the improved aftertreatment can reduce the increased NO_x. Consequently, propulsion materials are required that can withstand higher pressures and temperatures. These advanced materials are an enabler for cost-effective fuel savings. Given the long timeline for the identification, development, and implementation of new materials, it is essential that R&D continues without interruption.

ENGINE SYSTEMS PROGRAM: STATE OF TECHNOLOGY AND GOALS

As with any power generation device using chemical reactions to provide energy, both diesel and gasoline engines have thermodynamic constraints associated with the combustion process. These engines have additional practical constraints as well:

• Impracticality of extremely large expansion ratios,
• Inability to capture all of the useable energy in the heat rejection and exhaust flow,
• Inability to totally eliminate pumping work,
• The presence of friction due to rubbing contacts, and
• The work consumed in driving auxiliaries and accessories.

All of these constraints add up to limit the efficiency that can be obtained from practical, economical engines. Figure 3-1-1 in Box 3-1 delineates the partitioning of energy within the engine between that for the engine and that for the vehicle. The fundamental causes of these limitations are known, and the 21CTP works to coordinate and advise the federally-funded programs focused on minimizing these limitations with technologies that would be viable in the market. The specific goals of the Partnership within the Engine Systems and Fuels area are the following (21CTP, 2013, p. 33):

Implicit in all of the above goals is meeting emission regulations. In the NRC Phase 2 review this was a significant focus because new emissions regulations had just come into effect (NRC, 2012). These standards were met through the development and integration of new emissions control technologies into the engine system. This exemplified a transition to a new combustion system development paradigm—synergistic integration of engine and fuel combustion development to most effectively utilize aftertreatment system capabilities.

Exhaust Emissions

The considerable effort and research funding focused on improving emissions control systems is complementary to the development of engine combustion processes. To meet US2007 HD regulations, exhaust gas recirculation (EGR) combustion strategies were the primary NO_x reduction technology, while diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) were the primary hydrocarbon (HC), carbon monoxide (CO), and particulate matter (PM) reduction technology (EPA, 2000). A transition occurred to meet the US2010 HD regulations since EGR was not sufficient to efficiently meet the required 0.2 grams per brake horsepower-hour (g/bhp-hr) NO_x tailpipe emissions levels. Selective catalytic reduction (SCR) was added to medium- and heavy-duty vehicles (MHDVs) to meet this new NO_x requirement, while some engines were sold without SCR because some manufacturers used credits to meet an average NO_x standard. Because the SCR can effectively remove NO_x, the US2010 engines could then operate at higher engine-out NO_x levels and run more efficiently. For Class 8 truck engines, this resulted in about a 5 percent reduction in fuel consumption for US2010 engines compared to US2007 engines. However, the trade-off required about 2 to 3 percent urea (contained in the diesel exhaust fluid [DEF]) relative to fuel (Charlton, 2010).

The requirements were adjusted again in 2013-2014, when onboard diagnostics (OBD) (2013) and the first phase of HD greenhouse gas (GHG) regulations (2014) were introduced. In conjunction with this, engine and emissions control systems were further optimized for better performance and/or reduced cost.

Now, emissions control technology needs further understanding to optimize performance, to reduce cost and fuel consumption, and to meet any future regulatory tightening.

Engine Systems Program

The industry has demonstrated great technical competence in reducing fuel consumption and meeting the 2010 emission standards while making a product that meets customers’ reliability and cost of operation goals and also the Environmental Protection Agency’s (EPA’s) 2014 GHG standards. What facilitates the industry’s achievements is the continued progress in understanding the technical subtleties of the thermodynamic, chemical, and physical processes involved in the conversion of the fuel energy into power. As the demands for higher efficiency and low emissions grow, so too does the need for an increasingly deeper understanding of the fundamentals. This is the principal deficit that the Engine Systems program of the 21CTP is facing as it works to achieve its efficiency goals (21CTP, 2013, pp. 40-41). The challenges specifically relating to engine system fundamentals are these:

• Inadequate understanding of the thermodynamic, chemical, and physical fundamentals of combustion and the consequent inability to incorporate them into robust simulation capabilities, especially across the full range of combustion approaches, from conventional diesel combustion to new low-temperature combustion (LTC) regimes.
• Inability to optimize in-cylinder combustion processes for efficiency via synergistic coupling of enhanced aftertreatment system performance.
• Lack of exploration and development of innovative engine processes and architectures.

The above challenges motivate the fundamental research and development projects in the 21CTP.

Although SuperTruck is discussed at greater length in Chapter 8, its engine development activities in SuperTruck are discussed here separately, before the individual DOE and Department of Defense (DOD) engine programs. SuperTruck’s engine programs interface closely with the 21CTP fundamental engine projects and are synergistic with them in achieving two of the Engine Systems’ program goals: the 50 percent BTE demonstration and the technical roadmap to 55 percent BTE. The discussion as a whole is separated into activities directed toward demonstrating 50 percent BTE on the road in a truck (Goal 1), which is a SuperTruck engine accomplishment, and then covers the activities showing a technical pathway to 55 percent BTE (Goal 2). The discussion of the SuperTruck engine teams’ work toward achieving Goal 2 segues into the discussion of the individual DOE and DOD programs nicely because of the extent to which the SuperTruck programs will be relying on the advancements made within the individual DOE and DOD projects to achieve the 55 percent goal. This is the sequence in which the research activities are discussed.

Research Budgets for the SuperTruck Program

Funding for the SuperTruck engine and vehicle program comes from two sources: the American Reinvestment and Recovery Act (ARRA) and the DOE Vehicle Technologies Office (VTO). The Cummins-Peterbilt and Daimler programs are funded through the ARRA, while the Volvo and Navistar programs are funded through the DOE VTO. There is no specific budget line item for engine development

TABLE 3-1 Estimated Federal Budgets for SuperTruck Engine Research (millions of dollars)

within the ARRA-funded programs, Cummins-Peterbilt and Daimler. However the Partnership did provide estimates to the committee. These estimates and the engine research budgets for Volvo and Navistar, along with the total budgets of federal dollars, are given in Table 3-1.

Progress Toward Meeting Engine Goals 1 and 2

The demonstration of 50 percent BTE in a truck on the road involved integrating laboratory-proven technologies into a vehicle powertrain system, with an eye toward assessing the viability of those technologies for commercial introduction. The SuperTruck program was developed around this goal. Accomplishments in this effort are highlighted here via a table of technologies used, which has been extracted from the more comprehensive Table 8-1 given in Chapter 8. The extension of this effort to reach 55 percent BTE entails a fundamental research program to explore and quantify the potential of using advanced combustion/fuel and engine technologies that are currently being explored within research laboratories, with an eye on showing technical potential. The activities of the SuperTruck teams are closely aligned with, and will depend on the results of, the individual research programs within 21CTP. The approaches each team is taking toward this goal are summarized in the paragraphs below.

Goal 1: Develop and demonstrate an emissions-compliant engine system for Class 7-8 highway trucks that achieves 50 percent brake thermal efficiency in an over-the-road cruise condition.

Status: The Partnership has successfully achieved this goal. As shown in Table 3-2, two of the four SuperTruck teams have successfully demonstrated brake thermal efficiencies greater than 50 percent in on-road tests using commercial, ultra-low-sulfur diesel fuel.

Both Cummins-Peterbilt and Daimler are in the final stage of their SuperTruck program. Their programs end in 2015, whereas Volvo and Navistar are in earlier phases of their programs. Both the Volvo and Navistar projects have completion dates in 2016. Their not having achieved Goal 1 is attributed to not being as far along in their programs as the other two teams. It is expected that they will meet their goal of 50 percent by the time they will have completed their work.

TABLE 3-2 Achievement of Goal 1, 50 Percent Engine BTE at Cruise, by the Four SuperTruck Teams

NOTE: WHR, waste heat recovery.

Table 3-3, which is extracted from Table 8-1, shows the engine and combustion technology that the respective SuperTruck teams are using in the 50 percent BTE engine. Each of the technologies being used can be categorized in terms of the second and third columns of the energy partitioning Figure 3-1-1. Each technology is used either to enhance the work extraction or to reduce the work expenditure for pumping, friction, accessories, and auxiliaries.

Achieving 50 percent BTE in a truck on the road, Goal 1 represents the successful integration of laboratory-proven technologies into a complex vehicle powertrain system, and the committee congratulates the Partnership and SuperTruck teams for this accomplishment.

Goal 2: Research and develop technologies that achieve a stretch thermal efficiency goal of 55 percent in prototype engine systems in the lab (by 2015).

Status: To date this goal has not been achieved, but progress has been good. It is anticipated that by the end of each of the respective SuperTruck programs, the teams will have developed a technology pathway for achieving 55 percent BTE. It is expected that the pathway will be combinations of individual technologies that are either demonstrated in the laboratory or simulated via advanced computational fluid dynamic (CFD) models.

Approaches to Meeting Goal 2

During the review, the committee heard presentations from the SuperTruck teams at its meetings, and made site visits to Cummins (August 28, 2014), Daimler (November 24, 2014), and Volvo (December 5, 2014). Achieving 55 percent BTE with a Class 7 or a Class 8 HD truck engine will be extremely challenging. The aggressiveness of the SuperTruck research programs is consistent with the high risk approach that needs to be pursued if this goal is to be

TABLE 3-3 Summary of Engine Technologies Used by the Four SuperTruck Engine Teams in Their Efforts to Achieve 50 Percent BTE on the Road in a Heavy-Duty Truck

NOTE: FMEP, friction mean effective pressure; PCP, peak cylinder pressure; HPCR, high-pressure common rail; CR, compression ratio; HVAC, heating, ventilation, and air conditioning; LED, light-emitting diode; EGR, exhaust gas recirculation; VG, variable geometry; HPL, high-pressure loop.

achieved. From a generic perspective, there is similarity in the overall approach being followed by the four teams. All of the programs are pursuing continued reduction in friction and pumping, more effective air boosting systems, smaller auxiliary and accessory loads, and improvements in their waste heat recovery (WHR) systems and are investigating advanced low-temperature combustion (LTC) approaches. All of the teams are also engaged with the aftertreatment technical community looking to capitalize on further improvements in exhaust gas treatment of criteria pollutants that will allow further optimization of the engine-aftertreatment combination. However, the details of how these technologies will be applied and the gains from each differ from program to program.

The basic premise of LTC processes stems from an understanding of the energy flow partitioning presented in Box 3-1 at the beginning of this chapter. If the in-cylinder temperatures can be kept low during the closed portion of the cycle, the thermal efficiency will increase. This is explained by the dependence of the closed-cycle efficiency of the engine on the ratio of the specific heats of the gases (γ = c_p/c_v) in the cylinder.² Lower temperatures and leaner mixtures within the cylinder result in values of gamma (γ) that are larger than when the temperatures are higher or the mixtures are stoichiometric. A larger average gamma results in more work being extracted during the closed cylinder portion of the engine’s mechanical cycle, which subsequently decreases the amount of useful energy leaving the energy in the exhaust. Furthermore, lower in-cylinder temperatures also result in less heat transfer from the cylinder.

The challenge with trying to drive the in-cylinder temperatures down is that the burning velocity of the fuel and air mixture decreases as the temperature decreases, and in trying to push this concept to the limit, the time necessary to complete combustion gets too long and engine efficiency and emissions suffer. The overview of the individual teams’ programs shows that shortening the combustion interval is an important aspect of achieving the 55 percent target. The general approach in LTC strategies is to keep combustion durations short by minimizing the need for flame propagation through volumetric combustion via autoignition. Achieving this type of combustion is highly dependent on the chemical and physical characteristics of the fuel and requires very precise control of the thermokinetic state of the air–fuel mixture within the cylinder. Understanding the fundamentals of these phenomena is prerequisite to success and is a principal focus of the individual DOE engine combustion research projects in 21CTP.

Researchers have proposed many different approaches for achieving LTC. They will typically name their specific approach with an acronym, such as HCCI (homogeneous-charge compression ignition), PPCI (partially-premixed-charge compression ignition), RCCI (reactivity-controlled compression ignition)—often more generically referred to as dual-fuel combustion—and many more. One advantage of the dual-fuel approach is that using varying ratios of two fuels with different degrees of reactivity gives the operating system an additional and powerful combustion phasing control lever. Indeed the dual-fuel approach is being investigated by most of the SuperTruck teams, although to date they have not divulged the specific fuel combinations they are currently exploring.

If successfully achieved, LTC strategies yield higher closed-cycle efficiency that minimizes heat loss from the cylinder and exhibits low NO_x and particulate emissions, but at the same time introduces concern about unburned hydrocarbon and carbon monoxide (CO) emissions. Consequently it is likely that aftertreatment will still be required, if not for PM and NO_x, then for HC and CO, and the aftertreatment systems will most likely need to operate at lower temperatures than current systems today.

Cummins

The Cummins approach to the 55 percent BTE requirement is described in its 2014 DOE Annual Merit Review (AMR) presentation (Project ACE057) (Koeberlein, 2014). Two basic combustion strategies are under evaluation. Both approaches will pursue downspeeding the engine and operating at higher loads to get the requisite power. The first approach, which uses relatively conventional diesel combustion, is summarized in Figure 3-1.

The approach embodied in the technologies listed in Figure 3-1 represents a continued effort at improving conventional diesel combustion. The optimized bowl, injector, and heat-transfer efforts represent combustion improvement. The team is performing simulation and experiments with the objective of shortening the combustion interval as much as possible to maximize the work from expansion and minimize heat loss. As shown in Figure 3-1, the objective is to gain approximately three percentage points improvement in engine BTE through this combustion improvement.

In addition to trying to further improve conventional diesel combustion, the Cummins-Peterbilt team is also pursuing a dual-fuel LTC strategy it calls alternate fuel compression ignition (AFCI). Simulation and laboratory results indicate that there is sufficient potential for improvement from this combustion strategy to merit further investigation. The

FIGURE 3-1 Cummins-Peterbilt SuperTruck team’s projected incremental gains to get from its current 50 percent BTE engine to 55 percent BTE. SOURCE: L. Kocher, “SuperTruck 55% BTE Update Technology and System Level Demonstration of Highly Efficient and Clean, Diesel Powered Class 8 Trucks,” presentation to the committee, Columbus, Indiana, August 28, 2014, slide 20. SuperTruck Annual Merit Review Presentations, Cummins, Inc.

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² C_p, specific heat at constant pressure; C_v, specific heat at constant volume.

FIGURE 3-2 Cummins-Peterbilt SuperTruck team’s analysis and results using AFCI at 1,000 rpm and 10 bar. SOURCE: L. Kocher, “SuperTruck 55% BTE Update Technology and System Level Demonstration of Highly Efficient and Clean, Diesel Powered Class 8 Trucks,” presentation to the committee, Columbus, Indiana, August 28, 2014, slide 24. SuperTruck Annual Merit Review Presentations, Cummins, Inc.

team’s current results comparing both the predictions and actual engine results are shown in Figure 3-2.

The simulation does a reasonably good job of predicting the engine-only performance. However, because the exhaust energy was lower with AFCI, the work output from the WHR system in the exhaust was lower than that from conventional diesel combustion. The Cummins AFCI approach shares challenges with other LTC strategies, including the difficulty of running the engine above 10 bar brake mean effective pressure (BMEP). Cummins plans additional work to find ways of increasing the BMEP limit. It expects the efficiency of the engine to improve as it achieves higher loads with AFCI.

Daimler–Detroit Diesel³

The Daimler approach to the 55 percent BTE requirement is described in the team’s most recent AMR presentation (Project ACE058) (Singh, 2014). The approach plans to use both downspeeding and downsizing of the engine. An overview of its 55 percent BTE scoping activities is presented in Figure 3-3.

Additional work on liner cooling optimization is ongoing with the Massachusetts Institute of Technology (MIT), as well as the development of new lubricants and optimization of the oil pump and lube circuits to reduce lube system power demand and further upgrades to the WHR system. Daimler-Detroit Diesel believes it may be possible to improve the WHR system contribution from 2.4 points of engine BTE (achieved in the final SuperTruck demonstration engine) to 3.6 points of BTE but acknowledges that this level of performance may prove impractical with currently available technology. As with other teams it is exploring the potential of LTC for shorter combustion intervals and lower heat loss. The team is working with the Oak Ridge National Laboratory (ORNL) on a dual-fuel engine approach, using natural gas as one of the fuels.

FIGURE 3-3 Overview of Daimler SuperTruck team’s approach to achieving 55 percent BTE. SOURCE: Singh (2014). NOTE: E-TC, electronic turbocharger; CR, combustion ratio; LTC, low-temperature combustion; HRR, heat release rate; WHR, waste heat recovery; EGR, exhaust gas recirculation.

Volvo

To achieve the target of 55 percent BTE, Volvo is pursuing different engine architectures, alternative combustion cycles, and fueling optimization (Project VSS081) (Amar, 2014). These approaches will be pursued in a downsized and downspeeded engine.

New combustion concepts like PPCI and RCCI have demonstrated very high indicated efficiencies as well as low engine-out emissions. However, these kinds of combustion are significantly more difficult to simulate than normal diesel diffusion combustion. So, enhancements to the simulation capabilities are under way. A transported probability distribution function (PDF) combustion model has been developed to address this challenge, which is backed up by extensive testing. A cetane ignition device equipped with optical access is used for testing of fuels and validation of spray and chemical kinetics submodels. Figure 3-4 shows a stack chart of where Volvo believes the improvements in engine processes can be made to achieve 55 percent BTE.

The Volvo SuperTruck program is leveraging Sandia National Laboratory’s Engine Combustion Network to validate the CFD subprograms it is developing. The team stated

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³ Detroit Diesel Corporation is a subsidiary of Daimler Trucks North America.

FIGURE 3-4 Volvo SuperTruck team’s stack chart of the incremental improvements in engine technology to reach 55 percent BTE from a concept demonstration powertrain. SOURCE: A. Greszler, “SuperTruck Development and Demonstration of a Fuel-Efficient Class 8 Highway Vehicle,” presentation to the committee, May 14, 2014, slide 14. Volvo Group Truck Technology.

that it is exploring a different engine architecture and running its heavy-duty engine on gasoline-like fuels, simulated as an 87 octane primary reference fuel blend.

Navistar

Navistar is also pursuing an aggressive research path in the technologies it has identified to achieve 55 percent BTE. Its approach includes downspeeding. Navistar’s simulation predicts that through continued improvements of the aftertreatment system, which will allow more efficient combustion phasing, advanced turbomachinery, thermal barrier coating, dual-fuel combustion with variable valve actuation, continued reduction in friction and parasitic losses, and incorporating an advanced organic Rankine cycle (ORC) as a WHR system, it will be able to achieve the 55 percent BTE target. An overview of the incremental gains it expects from these technologies is shown in Figure 3-5.

Progress and Fundamental Programs Toward Overcoming Technical Barriers to Achieving 55 Percent BTE (Goal 2)

As seen in the descriptions of the SuperTruck team’s activities, advanced combustion strategies and sophisticated CFD modeling are essential parts of their technical roadmaps to achieving 55 percent BTE. The requisite understanding of the fundaments of advanced combustion strategies, like LTC, and incorporation of that understanding into usable CFD codes is the focus of the individual research programs within 21CTP. Success in achieving Goal 2 will depend on the advancements being made within the individual 21CTP research programs.

The Partnership has increased its emphasis on incorporating their research results into simulations or conceptual models that can be used by stakeholders for either predictive simulation or for comparative analysis with laboratory results to gain an understanding of the data that is not achievable through routine analysis. Additionally, the development of phenomenological models, which conceptually model the different processes occurring within the engine, helps others in the field to understand the differences between processes that appear to be similar globally but are fundamentally different, e.g., different LTC approaches relative to conventional diesel or direct ignition combustion.

The 21CTP has been successful in its engine research efforts to increase BTE. Advanced CFD is being used extensively by all of the SuperTruck engine teams. Optimization of the combinations and interactions of the myriad of parameters that affect the efficiency and emissions of the complex engine systems could not have been done without advanced CFD. Details of the fuel spray breakup, how it depends on what is occurring inside the nozzle, and how the fuel then mixes with the combustion chamber gases and is impacted by the fluid motion within the chamber, along with the influence of the composition of the chamber gases on the nature of the energy conversion process, all impact the efficiency and emissions of the engine. As the industry tries to push the limits of efficient engines by lowering the engine-out emissions, an understanding of these details, as well as other phenomena like the localized boundary layer heat transfer, the state of thermal gradients within the chamber, and the evolution of the fuels’ reactivity, becomes critical. CFD simulations with accurate submodels of the thermodynamic, chemical, and physical processes occurring in the engine and the aftertreatment systems enable these activities, and will need to be advanced further to facilitate achieving Goal 2, 55 percent BTE.

DOE programs have made significant contributions to the capabilities of the CFD programs. The continued development of more accurate, high-fidelity, kinetic routines for different fuel mixtures has been an important contribution. An industrial collaborator, Convergent Science, has licensed a kinetic solver developed through DOE research programs and is now using its code to do simulations with these advanced kinetic routines and fluid mechanic models for many in the engine industry. Argonne National Laboratory (ANL) is preparing to launch a program called the Virtual Engine Research Institute and Fuels Initiative (VERIFI),⁴ an organization that will be available to industry and that integrates high-performance computing, fuel chemistry, and combustion science and engine performance with some of the world’s fastest supercomputers. This organization will facilitate simulations that industry does not have the capital resources to do but that are important to achieving the goals

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⁴ For more on the VERIFI program at ANL, see http://verifi.anl.gov/.

FIGURE 3-5 Navistar SuperTruck team’s projected improvements in the engine technologies that will enable them to achieve 55 percent BTE. SOURCE: R. Nine and R. Zukouski, “SuperTruck–Development and Demonstration of a Fuel-Efficient Class 8 Tractor & Trailer Vehicle System,” presentation to the committee, November 18, 2014, slide 12.

set for engine systems relating to reduced fuel consumption and lower emissions.

Because of the importance of CFD as a development tool, along with the rapid pace at which computing technology is changing, DOE held a high-performance computing workshop on August 19-21, 2014. The purpose of the workshop was to get feedback from users and stakeholders on the best way to integrate new research results into simulations. Discussion was on topics such as these: Is there a preferred platform by which newly developed subprograms can be publically demonstrated and critiqued? What is the appropriate role of the government in this arena? The outcomes of that workshop were not available at the writing of this report, so they could not be included in this report.

Finally, an anecdote about the success of the 21CTP: During a site visit to the Tank Automotive Research, Development and Engineering Center (TARDEC) on November 24, 2014, a subgroup of the committee was told that results from the 21CTP have been influential in production decisions on light- and medium-armored vehicles and on decisions about power plants and powertrains.

Individual DOE and DOD Engine Systems Projects and Funding Levels

As part of the review process, the Partnership supplied to the committee a listing of the projects in its research portfolio. The projects from that list that the committee has interpreted as falling within the advanced engines arena are listed in Table 3-4. They include the TARDEC Automotive Research Center, run by the University of Michigan, and the DOE programs that are focused on advancing the fundamental understanding of engine processes. As mentioned above, a committee subgroup visited TARDEC as part of the fact-finding effort. During that visit, the subgroup was told about an advanced engine program in which innovative combustion processes and an alternative engine architecture are being assessed as a high-power-density engine with improved efficiency. The presentation on this work indicated that the opposed-piston two-stroke diesel engine met or exceeded program requirements for improved BTE, heat rejection to coolant, power density, and a 50-hr durability test. In the request for proposals for the next phase of this development program, DOD specifically required the opposed-piston architecture. The results of the proposal evaluations have now been made public. TARDEC awarded two contracts, one to the Achates-Cummins team and the other to the AVL group, to design, build, test, and evaluate advanced single-cylinder (SC) opposed-piston engine technology for potential future combat vehicle applications. Both teams were given the same combat engine performance parameter targets that are representative of multicylinder engine performance expectations. The performance parameters include these:

1. Specific heat rejection of 0.45 Kw/kw, which includes charge air cooling, water jacket cooling, and engine oil cooling,
2. A best brake specific fuel consumption point of 0.32 lb/bhp-hr,
3. A rated speed air:fuel ratio not to exceed 30:1,
4. A targeted rated speed of 2,600 rpm,

TABLE 3-4 Research Projects Identified by 21CTP as Part of the Engine Systems Program (dollars)

NOTE: Information provided includes project number, title, lead organization, and federal dollars supporting the program.

5. A rated speed power of 250 bhp and a minimum peak torque of 500 ft-lb,
6. Military fuel use compatibility encompassing jet and diesel fuels, and
7. Steady-state and transient smoke targets not to exceed visible limits. Both efforts also include a conceptual multicylinder engine study that targets representative combat vehicle claim space.

Although not officially categorized as part of the 21CTP program, this opposed-piston engine technology is worthy of mention because exploration of nonconventional engine architectures is an area of interest for the 21CTP.

The total 2014 federal budget for all of the DOE Engine Systems projects listed in Table 3-4 is $6.52 million. The committee was not given the federal dollar budget for the DOD-funded Automotive Research Center at the University of Michigan, so a sum total of all the engine research activities aside from the SuperTruck engine program is not known. Investigators for each of the engine systems projects with DOE funding are required to submit quarterly progress reports, participate in semiannual research progress meetings, and give a presentation at the DOE AMR. Each AMR presentation states the project’s relevance, the budget, milestones for the project, the technical approach, accomplishments, lists of collaborators, and future work. The presentations and the reviewers’ comments are available to the public.⁵

Brief Summary of DOE Individual Programs

The Engine Systems research programs listed in Table 3-4 span a range from fundamental experimental work, to kinetic mechanism development, to mechanism evaluation and simplification, to development of advanced numerical methods, and further development of the computational codes. The program is well managed and there is good collaboration and synergy between the individual DOE 21CTP engine projects. Brief summaries highlighting the accomplishments for each of the DOE projects shown in Table 3-4, along with links to the 2014 Annual Merit Review presentations, are given below.

Project ACE001. Using in-cylinder optical imaging, Musculus has developed a conceptual model of direct injected LTC, and the bridging between conventional combustion and LTC (2014). The model along with the in-cylinder imaging shows the spatial and temporal evolution of soot precursors. These soot evolution histories compared favorably with simulations that were performed as part of a collaboration with the University of Wisconsin. Musculus’s research has also shown how injection rate shapes affect postinjections and how piston bowl geometry affects multiple injections.

Project ACE004. Dec and collaborators General Motors, Cummins, LLNL, University of California-Berkeley, University of Melbourne, and Chevron have demonstrated a peak indicated thermal efficiency of 49.8 percent and were able to explore the maximum load that could be achieved using homogeneous charge and direct injection partially stratified charge compression ignition of gasoline-like fuels (Dec, 2014). Maximum loads in excess of 16 bar BMEP were achieved, and it was concluded that significant noise reduction could be achieved with a minimal loss of thermal efficiency.

Project ACE005. Through the research efforts of Pickett and his research team, the Spray Combustion Cross-Cut Engine Research Network continues to grow (Pickett and Skeen, 2014). This network represents a collaboration among approximately 20 international laboratories, industries, and universities dedicated to a coordinated experimental and computational evaluation of engine-relevant spray conditions for the purpose of developing predictive computational tools that can be used by industry. The dissemination and collaboration is done through Sandia’s Engine Combustion Network.⁶

Project ACE007. In conjunction with the modeling efforts taking place as part of the Engine Combustion Network, Oefelein and his research team are continuing the development of large eddy simulation (LES) to facilitate more accurate spray and fluid mixing simulations (Oefelein et al., 2014). Trying to understand the underlying causes of cycle-to-cycle variation, correctly simulating the differences between gasoline and diesel sprays, and predicting the effects of internal nozzle geometry on the spray processes in the cylinder is currently outside the precision and fidelity of the models. Such work provides a link between the DOE Office of Science and the VTO.

Project ACE010. Dr. Powell and his research team at ANL are using the laboratory’s unique Advanced Photon Source (APS) to perform x-ray measurements of near-nozzle and intra-nozzle phenomena on production-type fuel injectors (Powell, 2014). They have been able to make detailed measurements of the internal nozzle needle wobble that occurs during injection and have measured the cavitation of the fuel inside the nozzle and the effects these phenomena have on injection and on injection variation. These results have been incorporated into the work of the Engine Combustion Network. Collaborators in this work include Delphi, Caterpillar, the University of Massachusetts-Amherst, and computational colleagues at ANL.

Project ACE012. The simulation of advanced compression ignition combustion processes, often generically referred to as LTC, requires detailed high-fidelity kinetic

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⁵ See Vehicle Technologies Office: Annual Merit Review and Peer Evaluation at http://energy.gov/eere/vehicles/vehicle-technologies-office-annualmerit-review-and-peer-evaluation.

⁶ See the Engine Combustion Network at http://www.sandia.gov/ecn/.

representation of the fuel and the in-cylinder fluid mechanics. Whitesides and his research team at LLNL are working on developing faster and more accurate combustion solvers to facilitate these calculations and evaluate the results using these solvers (Whitesides et al., 2014). The emphasis of this project is to use the advanced solver as a means of validating detailed engine and combustion modeling tools through simulation of LTC results from a variety of collaborators.

Project ACE013. In conjunction with the more efficient solvers, it is important to also have comprehensive, high-fidelity kinetic routines to simulate the in-cylinder combustion process. This is the focus of Dr. Pitz and his research team’s efforts (Pitz et al., 2014). They are developing predictive chemical kinetic models for gasoline, diesel, and next-generation fuels by creating surrogate fuels, which are fuel blends in which the number of components in the fuel is computationally manageable. They are developing models for FACE, which include blends that have been specified for researchers to represent a matrix of fuels in which the properties vary over a range that might be expected in the future as feedstocks change. The diesel surrogate fuel under investigation currently has nine components, a mixture of selected n-alkanes, isoalkane, cycloalkane, one- and two-ring aromatics, and a napthoaromatic. Their current gasoline surrogate has 10 components. Their work involves collaboration with many who are performing experiments and simulations to assess the representativeness of the surrogate fuels to actual fuels, and to assess the accuracy of their kinetic routines.

Project ACE014. At LANL, DOE is supporting Dr. Carrington to write the next version of KIVA, the open source software program that has been used extensively as the framework for past engine CFD simulations (Carrington, 2014). Dr. Carrington is collaborating with the University of New Mexico, Purdue University, Calumet Specialty Products Partners, L.P., the University of Nevada-Las Vegas, and many KIVA users. The new version, KIVA 4, uses a high-performance finite element method in a modular object-oriented parallel processing code. This is being coupled to faster grid generation capabilities. The general topic of advanced CFD program development, which includes the KIVA 4 program, was the focus of DOE’s High Performance Computing Workshop.

Project ACE015. At ORNL, DOE is supporting analysis of fundamental thermodynamic strategies and implementation methods that could provide an increase in efficiency that would be revolutionary rather than evolutionary. Daw and his colleagues are analyzing the potential of reformate assisted dilute combustion through thermochemical recuperation (Daw et al., 2014). They are looking at steam reforming the fuel—octane, ethanol, or methanol, for example—to maximize the fuel’s exergy while facilitating highly dilute combustion, which would reduce heat transfer and improve the working properties of the gas. Catalyst performance experiments have been performed and an engine test is under development. The research team is collaborating with SNL, the Gas Technology Institute, Cummins, the University of Michigan, and Pennsylvania State University.

Project ACE052. Toops and his research team are exploring the use of nondestructive neutron imaging to visualize the internal flow dynamics in fuel injectors and the buildup of soot and ash in diesel and gasoline particulate filters (Toops et al., 2014a). Images can be obtained at a single cross section or a complete reconstruction can be constructed to provide a cross section of the entire sample at a resolution on the order of 10-20 microns. Voids in the nozzle’s fuel reservoir can be detected. This work is in collaboration with the DOE Office of Basic Energy Sciences, the University of Tennessee, MIT, the University of California, GM, and NGK Spark Plugs.

Project ACE054. Goldsborough and colleagues at ANL are using their rapid compression machine to acquire fundamental data that will be used to develop and evaluate kinetic routines for transportation-relevant fuels at conditions representative of advanced combustion regimes (Goldsborough et al., 2014). This work is being done in collaboration with DOE Basic Energy Sciences, LLNL, King Abdullah University of Science and Technology (KAUST) and Chevron, the University of Wisconsin, and the DOE working groups on HCCI and diesel engines. The behavior of FACE and the comparison to the predictions of that behavior using kinetic mechanisms from the surrogate models is one of their projects. They are also evaluating the impact of fuel additives such as ethylhexyl nitrate (EHN).

Project ACE075. Som and his colleagues, also of ANL, are pursuing advances in fuel spray and combustion modeling for compression ignition engine applications (Som et al., 2014). This is a comprehensive program with collaborations among other groups at ANL, Convergent Science, Caterpillar, Cummins, LLNL, the Sandia Engine Combustion Network, the Advanced Engine Combustion Working Group, the University of Connecticut, and the Politecnico di Milano and University of Perugia. Simulations are being done for flow inside the nozzle tip, with 50 million computational cells, using the data from the images of the internal nozzle and needle tip motion obtained in the advanced photon source research. The simulations show the complexity of the flow inside the nozzle, how it is impacted by needle wobble, and how it impacts the spray behavior when the flow enters the cylinder. These are the capabilities that will be made available to participants in the VERIFI program, mentioned above.

Project ACE076. McNenly is the principal investigator of the program at LLNL, which is focused on the development of improved solvers for advanced engine combustion simulation (McNenly et al., 2014). Colleagues of this research team are also evaluating the effectiveness of the developed solvers to validate detailed engine and combustion models for a variety of LTC engine results, see discussion above. In the development of the solver, better algorithms and applied mathematics are being coupled with new Graphical Proces-

sor Unit (GPU) computing architecture to facilitate inclusion of improved physical submodels for better accuracy and smaller error. This is especially important as the number of species in the simulation grows. Currently, the team has demonstrated a 4.8-fold speedup over a conventional modern code for a simulation containing 2,000 species. Collaborators in this work include Cummins, Ford, Volvo, Bosch, GE Research, Convergent Science, Nvidia, ANL, National Renewable Energy Laboratory (NREL), SNL, FACE, the Advanced Engine Combustion working group, and multiple universities.

Project ACE077. Finally, in a cooperative research and development agreement (CRADA) between ORNL and Cummins, Partridge and colleagues are developing and applying an advanced EGR probe to help characterize and reduce combustion variations (Partridge et al., 2014). The probe is a laser-based multiplex EGR probe that measures CO₂. Measurements are being made in the intake manifold to assess charge components and fluctuations by measurement of the residual gas backflow and external EGR. When combined with models, the nature of the residual gas in the cylinder can be predicted. This in turn will facilitate control of advanced combustion strategies. The team is also developing a multicolor, multispecies EGR probe that measures CO₂, water, and the temperature of the cylinder charge components. Other collaborators include the Cummins SuperTruck engine team and the University of Central Florida. This project was given a 2013 R&D 100 Award.

As seen in the brief summaries given above, the Engine Systems research programs range from fundamental experimental work, to kinetic mechanism development, evaluation, and reduction, to advanced numerical methods, and to further development of the computational codes. The committee believes that the program is well managed and there is much collaboration and synergy between the individual projects of the DOE 21CTP engine projects. And, the program is addressing some of the important technical barriers standing in the way of achieving 55 percent BTE, Goal 2.

Approaches to Goal 3

Goal 3: Through experiments and models with FACE and other projects, determine the most essential fuel properties, including renewables, to help achieve 55 percent engine brake efficiency (by 2014).

(When asked for clarification of the intent of Goal 3, Kevin Stork, DOE, responded that the fuels research in the 21CTP was to “support experimental and modeling work to determine the impacts of fuel properties on enhancing (or hindering) attainment of advanced combustion modes, such as LTC, over a greater portion of an engine map.”)

Status: A more detailed discussion of the fuels and lubricant research within the 21CTP is given in a separate section later in the chapter, so only general comments will be made here. The committee feels that fuel research is much more important than what is stated or implied in Goal 3. As mentioned in the preceding summary of DOE engine research, FACE provides researchers with the ability to perform experiments with fuels of known characteristics, having property ranges that are within the range of variations that might be seen in future fuels. This is superior to running specific blends of research grade fuels that are not representative of what an engine will experience in the field. Using FACE also helps with the kinetic model development being pursued in the surrogate fuel simulation program. Researchers can now test their advanced kinetic models against realistic, but known, fuels in real engines, an important step in developing simulation capabilities for predictive behavior. The committee believes a more detailed understanding of the impact of fuel characteristics on engine operation and potential facilitation of advanced combustion will also enable the high-level objective of maximizing the utility of our fossil fuels, thus reducing their use.

Partnership Responses to NRC Phase 2 Recommendations: Engine Systems

Committee Comment on 21CTP Responses

The committee is pleased with the responses by 21CTP to the NRC Phase 2 recommendations. Unfortunately there has not been a DEER Conference since the Phase 2 review, so DOD participation has not been possible. The committee commends DOE and DOD for the formation of the Advanced Vehicle Power and Technology Alliance.

Findings and Recommendations: Engine Systems

Finding 3-1. The 21CTP has successfully met Goal 1, to develop and demonstrate an emissions-compliant diesel engine system for Classes 7 and 8 highway trucks that achieves 50 percent brake thermal efficiency in an over-the-road cruise condition. The engine uses a waste heat recovery system.

Finding 3-2. The projects in the engine systems portion of 21CTP represent a closely coordinated set of research activities that are pursuing a better fundamental understanding of processes critical to efficient engine operation. Fundamentals associated with fuel injection, sprays, gas exchange, in-cylinder flows, advanced combustion processes, plus comprehensive yet robust kinetic routines for realistic fuels are being investigated. The learning from these activities is being incorporated into models, both detailed and phenomenological, which serve as tools for advanced engine development. Integral to this effort is the continued advancement of the base computer program itself and the solvers that facilitate rapid computational turnaround time. The program is well managed and interfaces well with industry stakeholders.

Finding 3-3. The 21CTP has realized the importance of transferring the new knowledge generated in its research programs into the stakeholder community and is active in disseminating this learning via appropriate forms and forums, such as the development of computer submodels that can be used by other researchers in the field, and through user groups such as the Engine Combustion Network, to maximize leverage and learning obtained from the research by encouraging broad base participation within the scientific community.

Finding 3-4. Increased emphasis has been placed on issues such as numerical algorithm development, advanced computer architectures, and CFD code development. The Partnership’s awareness of the importance of these activities was evinced by the high-performance computing workshop DOE sponsored in August 2014.

Recommendation 3-1. With the increased importance of advanced CFD for developing the engines and operating scenarios necessary for minimum fuel consumption and in light of DOE’s role in the generation of new knowledge that gets incorporated into these CFD codes as submodels, a critical review of the Partnership’s program to develop the next-generation code (KIVA 4) should be performed. Feedback from the participants of the high-performance computing workshop should be matched against the current code development activities, and the adequacy of the current program should be assessed. If necessary, the next-generation code development should be adjusted.

Finding 3-5. Achieving Goal 2, 55 percent BTE in a laboratory engine, will be very challenging. This is a high-risk, high-reward fundamental research program. It is an important stretch goal because it will facilitate identifying the potential of different advanced engine, fuel, and combustion concepts for increased engine efficiency, even though these concepts may not be commercially viable in the near future.

Recommendation 3-2. The fundamental diesel engine research program pursuing advanced technologies and combustion processes and engine architectures to achieve 55 percent BTE should continue to be a focus of the 21CTP engine activities. However, the experiments and modeling should maintain a focus on dynamometer R&D, as opposed to attempting to build a demonstration vehicle. The achievement of this goal should be extended from 2015 to 2020, in order to have sufficient time to carry out R&D on this stretch goal. Also, this activity should not be at the expense of efforts

to reduce load-specific fuel consumption via system integration and road load reductions.

AFTERTREATMENT SYSTEMS

Introduction

HD diesel aftertreatment systems have evolved worldwide as separate systems. Europe was developing and optimizing the SCR systems to meet Euro IV and V regulations (2005, 2008 respectively), while Japan and the United States were developing diesel particulate filter (DPF) technology. Both technologies came together to meet the US2010 and Euro VI (2013) HD regulations. New U.S. regulatory requirements went into effect in 2013 and 2014, when OBD (2013) and the first phase of the medium- and heavy-duty vehicle fuel efficiency and GHG regulations (2014) were introduced.

More-efficient SCR systems allow higher engine-out NO_x, resulting in further reduction in fuel consumption and low engine-out PM levels. The NO₂ levels coming out of the diesel oxidation catalyst (DOC) are sufficient in many 2013 engines to oxidize the PM retained on the filter without the need for high-temperature active regeneration. This resulted in filters with less PM mass and lower back pressure. An example of a modern emission control system architecture is shown in Figure 3-6.

The required OBD system adds significant complexity, with upwards of 18 control points, as illustrated in Figure 3-7 (Stanton, 2013). The OBD system is needed to diagnose deficiencies in the emissions control system and allow the defective parts to be identified to facilitate remediation. Major industry efforts are being expended on OBD, and emissions control system choices are always made in the context of OBD requirements.

The results of these efforts to date are quite impressive. In many cases the tailpipe concentration of fine particles is less than that of ambient air. NO_x reductions are approaching 98 percent from engine-out levels. In Europe, trucks have lower NO_x emissions per kilometer than modern diesel cars (Bergmann, 2013).

California is now independently considering another 90 percent reduction of the HD NO_x tail pipe standard for around 2020 (CARB, 2015). EPA may consider following with similar tightening depending on the level of the new National Ambient Air Quality Standard (NAAQS) ozone standard, proposed in December 2014 to be in the range of 65 to 70 ppb. To have minimal impact on fuel consumption, these new tail pipe NO_x levels (~0.02 g/bhp-hr) will require nominally 99.5 percent NO_x reductions on the hot federal test procedure (FTP) cycle and 96 percent reductions on the cold FTP cycle, both of which depend on additional innovations in emissions control technology. The California initiative will stimulate new approaches to HD NO_x aftertreatment, particularly related to cold start emissions. Some technologies being considered are SCR filters (SCR catalyst coated on DPF) to

FIGURE 3-6 Layout of a modern HD diesel emission control system. SOURCE: D. Stanton, “Systematic Development of Highly Efficient and Clean Engines to Meet Future Commercial Vehicle GHG Regulations,” SAE Int. J. Engines 6(3): 1395-1480. Reprinted with permission from SAE paper 2013-01-2421Copyright © 2013 SAE International.

FIGURE 3-7 Example of OBD layout for a 2013 HD aftertreatment system. SOURCE: D. Stanton, “Systematic Development of Highly Efficient and Clean Engines to Meet Future Commercial Vehicle GHG Regulations,” SAE Int. J. Engines 6(3): 1395-1480. Reprinted with permission from SAE paper 2013-01-2421 Copyright © 2013 SAE International.

add SCR catalyst closer to the engine, and low-temperature NO_x adsorbers that release the NO_x at higher temperatures when the SCR is functional. Further, at such high deNO_x efficiencies, proper management of the diesel emission fluid (ammonia) will be critical to prevent the formation of N₂O, a powerful greenhouse gas. Expected OBD requirements at these very low tail pipe NO_x levels are not achievable with today’s sensor and modeling technology.

Although 21CTP has no specific aftertreatment goals, in the February 2013 Roadmap (21CTP, 2013, p. 45), 21CTP listed several aftertreatment elements to the overall technical strategy:

• High-efficiency SCR.
• Resolve remaining issues on DPF regeneration, ash loading and removal, and aging.
• Mitigate sulfur effects.
• Improve the catalyst materials and systems for lean NO_x catalysis with urea and other reductants for performance over a wider temperature range while minimizing reductant slip.
• Develop monitors and thresholds for sensors in controls and diagnostics in conjunction with OBD. Develop and use fundamental knowledge of catalysts and sensors for OBD methods.
• Materials for catalysts and filters that have high efficiency, low back pressure, and minimal space requirements for at least 1 million miles of durability.
• Robust sensors with direct sensing of emissions constituents (e.g., PM, N₂O).

Aftertreatment Projects

The NRC Phase 2 report (2012) put the total spending during the previous 7 years of 21CTP heavy-duty truck aftertreatment work (through FY 2010) at about $37 million. Spending FY 2011 through FY 2014 was about $13 million, for a total of about $50 million of aftertreatment-related funding over 11 years ($4.5 million per year average). Table 3-5 describes the expenditures on active aftertreatment projects reported to the committee by 21CTP since the NRC Phase 2 review.

The aftertreatment research and development community is quite active, with upwards of 400 technical papers and presentations annually presented worldwide on industry- and government-funded work. In the opinion of the committee, the body of work sponsored by 21CTP ought to complement, not duplicate, the industrial programs. Following is a summary of the 21CTP project progress with comments on corollary work from outside the DOE projects.

TABLE 3-5 Expenditures on 21CTP Aftertreatment Projects (dollars)

Crosscut Lean Exhaust Emission Reduction Simulation (CLEERS) Program

The Joint Development and Coordination of Emissions Control Data and Models (ACE022 and ACE023) is a project managed by ORNL with subprojects managed by the Pacific Northwest National Laboratory (PNNL). The core activities are to support and coordinate emissions control research, which evolves with DOE priorities and industry needs. Efforts are communicated to the 22 industrial partners, 11 universities (including three in Europe), and two national laboratories through monthly teleconferences and an annual workshop that is open to the public. The 2014 workshop had more than 100 attendees, 39 technical papers, and 12 posters. Topics most pertinent to the 21CTP included diesel particulate characterization and filtration; SCR catalysts, reaction mechanisms, and modeling of urea spray; oxidation and reforming catalysts; passive adsorbers and traps; multifunctional catalysts and aftertreatment devices; emissions controls and engine integration; low-temperature catalysis; interpretation of experimental aftertreatment measurements; development of microkinetic and global reaction mechanisms; drive-cycle simulations of conventional and hybrid vehicles; and engine exhaust speciation. Examples of recent accomplishments of CLEERS are the provision of basic data in support of vehicle systems aftertreatment modeling; the establishment of a new online database for references relevant to modeling of emissions control devices; the analysis and reporting of results from a 2013 industry priority survey; the measurement of NH₃ storage isotherms on a commercial small pore Cu zeolite; the development and application of analytical techniques for extracting adsorption enthalpies from isotherm data; and the development of reaction mechanisms for NO SCR reactions that are consistent with reaction rate measurements and diffuse reflectance infrared spectroscopy (DRIFTS) observations. Future work will continue mechanistic investigations into small pore Cu zeolite and candidate NO_x adsorber materials, with emphasis on low-temperature operating conditions and will initiate the characterization of passive adsorber materials and protocols for their development.

Emissions Projects

Project ACE026. The CRADA project “Enhanced High and Low Temperature Performance of NO_x Reduction Materials” focuses on determining factors that limit low- and high-temperature NO_x performance, including mechanisms for deactivation for candidate materials due to hydrothermal aging and poisoning mechanisms. NO_x adsorber work that ended in 2014 shows enhanced potassia-titania high-temperature NO_x storage catalysts deactivated through irreversible

reaction of the two oxides. Work is now focused on preparing and modeling three emerging SCR catalysts with improved low-temperature and high-temperature performance. Model Cu/SAPO-34, Fe/SSZ-13, and SSZ-13 with various Si/Al ratios have been prepared for a number of studies of low- and high-temperature performance of commercial Cu-chabazite (CHA)-based SCR catalysts. These studies led, in part, to the identification of SCR catalyst materials with significantly lower (up to 20°C lower) “light-off” temperatures than the contemporary Cu-SSZ-13 catalyst. Future work will focus on limitations of low- and high-temperature performance of CHA-based SCR catalysts.

Project ACE028. The project “Experimental Studies for CPF and SCR Model, Control System, and OBD Development for Engines Using Diesel and Biodiesel Fuels” was completed in September 2012. A core aspect of the project was communication and collaboration between stakeholders to facilitate the achievement of emissions regulations with minimal fuel penalty for a wide range of engines, including those operating on diesel or biodiesel fuel. The project developed DOC, catalyzed particulate filter (CPF), and SCR reduced-order models and estimator strategies that were validated on engines for use in calibration efforts. Importantly, an industrial consortium was formed in 2014 to continue this work.

Project ACE032. The Cummins/ORNL-FEERC CRADA, “NO_x Control & Measurement Technology for Heavy-Duty Diesel Engines, Self-Diagnosing Smart Catalyst Systems,” is aimed at developing diagnostics to promote the understanding of both the SCR catalyst and the impact of aging on catalyst performance, focusing on distributed NH₃ storage and NO_x conversion performance. Accomplishments include assessment of impacts of hydrothermal laboratory aging on commercial SCR catalyst functions of NH₃ capacity, the SCR reaction, parasitic NH₃ oxidation, NH₃ oxidation characterization, and determining that the common approach using capillary sampling was noninvasive. Future work will be to extend the work to field aging and assess aging impacts via experimental correlations and comparison to catalyst models.

Project ACE089. “Development of Radio Frequency Diesel Particulate Filter Sensor and Controls for Advanced Low-Pressure Drop Systems to Reduce Engine Fuel Consumption,” has the objectives of developing radio frequency (RF) sensors and controls for direct, in situ measurements of DPF soot and ash levels; quantifying associated fuel savings; exploring additional efficiency gains with advanced combustion modes, alternative fuels, and advanced aftertreatment via RF sensing and control; and developing production designs and commercialization plans. The investigators completed preproduction RF sensors and antennas; demonstrated combined DPF soot and ash measurements; benchmarked RF transient response with an established microsoot sensor; evaluated RF performance over 240,000-mile equivalent DPF aging; and quantified fuel savings potential via extended regeneration intervals and reduced regeneration duration of about 50 percent relative to stock original equipment manufacturer (OEM) controls in a fleet test. Future work will focus on developing optimized calibrations and controls to quantify performance relative to baseline conditions in a wide range of engine and vehicle applications.

Materials Work at ORNL Related to Catalysts/Emissions

ORNL makes use of capabilities that are hard to maintain at universities and difficult to justify in industry, given the need for experienced researchers to operate and to maintain state-of-the-art equipment. One example is the aberration-corrected electron microscope (Project ID 18865), which provides atomic-level imaging to better than 1 Å resolution. Samples can be heated in situ up to 1,000°C and follow a catalytic reaction in a controlled atmosphere. Basic research studies have been followed using catalysts such as Au/CeO₂ and Pt/Rh on a perovskite. In other work (Narula et al., 2010) scientists at ORNL are using theoretical models to explore catalyst materials via first principles for low-temperature operation. Materials being explored are bimetallic zeolites such as CuFe ZSM-5.

Project PM055. In this project, “Biofuels Impact on Aftertreatment Devices,” ORNL is investigating the impact of biodiesel fuel on aftertreatment devices. Impurities (Na, Ca, and Mg) in biofuels have been found to accumulate on the aftertreatment devices. The sources of these impurities are NaOH and KOH from the transformation of the feedstock and Ca/Mg from the washing.

Project PM009. This project, “Materials Issues Associated with EGR Systems,” concerns soot in the exhaust that can deposit and interfere with the EGR system, causing the engine to lose BTE. Advanced engines EGR will be required to operate over a wider range of engine speed and loads. Low-temperature combustion will increase this problem and also hinder waste heat recovery. One approach is to identify the optimum operating temperature for the system. Imaging technologies are being applied to characterize the deposits. Strategies being explored include deposit removal techniques. U.S. diesel engine manufacturers are collaborating on this project with ORNL.

Project PM010. In a CRADA with Cummins, “Durability of Diesel Engine Particulate Filters,” ORNL is characterizing properties of ceramic diesel particulate filters and developing tools to assess durability and reliability. One goal is to be able to reduce the fuel economy penalty associated with the DPF by 25 percent relative to the baseline 2009 vehicle. The regeneration of the filter that is the focus of this work must be reliable and the filter durable. A new zeolite-based support with a finer pore structure is being investigated. The Cummins test rig is being used to do simulated measurements of filter lifetimes. Data generated will be used as input to models to predict the behavior of the DPF.

Project PM049. ORNL worked on this project, “Catalyst Characterization and Deactivation Mechanisms,” in two separate stages from 2009 through 2013. In one it partnered with Cummins and on the other with Ford, University of Michigan, and Protochips. The overall objective was cost-effective emission control using new engine operating conditions that minimize emissions. The approach was to increase understanding of the deactivation mechanisms and address durability requirements for light-duty diesel aftertreatment: ammonia oxidation (AMOX) and SCR materials. Hydrothermal aging was done at elevated temperatures for lifetime prediction and to evaluate degradation mechanisms. Transmission electron microscopy (TEM) provided atomic resolution of rhodium nanoparticles on a CaTiO₃ support over a wide temperature range and in an oxidizing-reducing atmosphere.

Other Emissions-Related Work Outside 21CTP

Fundamental or characterization work outside the 21CTP has been reported on many pertinent aspects of emissions control. Improvements in SCR catalyst formulations have been reported on Mn zeolites (Kim et al., 2012), improved Cu zeolites (Walker, 2012; Reith et al., 2013), SCR filter catalysts (Rohe et al., 2012), and advanced substrates and LT urea injection methods (Strots et al., 2014). SCR system durability and aging studies are reported by SwRI (Bartley et al., 2012), and Cummins (Yezerets et al., 2014; Chen et al., 2013; Kumar et al., 2013). Daimler and Milano Politecnico investigators showed NO_x can adsorb on SCR catalysts upon engine start-up, until water reaches the catalyst (Schmeisser et al., 2013). Dioxin emissions are minimal and not a concern, as reported by EPA (Laroo et al., 2013). Tenneco reported engineering and fundamental work on silver-alumina catalysts that use E85 as a reductant instead of urea (Patel, 2012). The University of Wisconsin (Viswanathan et al., 2012) and MIT (Kamp et al., 2013; Sappok et al., 2013) reported fundamental characterization of ash-soot interactions in DPFs. Soot regeneration by NO₂ on DPFs with SCR catalyst coatings is characterized by Liebherr (Hohl, 2014) and modeled by BASF (Tang et al., 2013). PGM-free DOCs were reported by Honda (Ishizaki et al., 2012) and Nanostellar (Wang et al., 2012). Heesung (Kim et al., 2013) and University of Pennsylvania (Cargnello et al., 2012) described new LT methane catalysts. Regarding technologies pertinent to California’s low-NO_x regulatory initiative, Theis and Lambert (2014) reported some work on the performance of low-temperature NO_x adsorbers, showing that the NO_x is stored on the base-metal storage material as a nitrite (from NO) using palladium as a catalyst, and the device is relatively resistant to sulfur poisoning and durable to 740°C. Not much is known about fundamental reaction mechanisms or the materials used in these components, and calibration studies are lacking on how they should be implemented. Michigan Technological University recently completed a thorough literature review on SCR+DPF system integration (Song et al., 2014). They identified several needs, including developing a testing protocol and a better understanding of ash-soot-catalyst interactions as they pertain to soot regeneration and SCR performance.

There are gaps in the literature pertaining to understanding or even reporting secondary or unregulated emissions, such as CH₄ or N₂O. Fundamental understanding on the formation mechanisms of the greenhouse gas N₂O from advanced combustion and emission control systems is lacking. This will become increasingly important as the GHG regulations tighten. Also, developments ought to be put into the context of the tightening HD regulations emerging in California and perhaps the EPA/NHTSA rulemaking in 2015.

Health-Related Studies

“Advanced Collaborative Emissions Study (ACES)” was a $15.5 million 7-year consortium program (2007-2013) in which the DOE was one of many partners. Completed in FY 2013, it characterized the emissions of US2007- and US2010-compliant HD engines and health effects of 2007 engines using a rat model. The emissions results are impressive. Particle number (PN) emissions on the FTP certification cycle for US2010 engines were reduced 99.9 percent from 2004 levels and 40 percent from US2007 levels, with this latter improvement attributed to the lack of active DPF regenerations in the 2010 engines (Khalek et al., 2015). On a custom 16-hour drive cycle, relative to 2007 engines, PM and PN emissions were reduced 71 percent, NO_x and NO₂ by 94 percent, hydrocarbons by 99+ percent, highly toxic dioxins and furans by 88 percent, and CO₂ by 3 percent. As reported in the final ACES health effects study (2015), health effects observed in rats after long-term exposure to diesel exhaust from new technology engines (compliant with 2007 regulations) were consistent with effects observed after exposure to NO₂ (NO₂ was reduced 94 percent in 2010 engines). Importantly, there was no increase in tumor formation over the background in the lung or any other organ compared to control animals; this was a major difference in long-term exposures to “traditional” diesel exhaust containing high levels of PM. Genotoxic endpoints showed no exposure-related changes. Some histopathologic changes observed in the gas-exchanging region of the lung were similar to changes after long-term exposures to oxidizing pollutant gases, such as NO₂ and ozone. There were few changes in respiratory function endpoints, which occurred more in females than males. Effects in the respiratory tract were mild and generally seen only at the highest exposure level. There were also few changes in inflammatory endpoints in blood, bronchoalveolar lavage, or lung tissue. Vascular endpoints were mostly unchanged, with a few scattered exposure-related changes (again mostly in females).

21CTP Response to Recommendations from NRC Phase 2 Review

The NRC Phase 2 review committee commented that significant progress was being achieved on emissions control understanding either through formal work in the program or through industry efforts. The only specific comments concerned researching CO₂ reduction pathways and characterizing particle number emissions to support future regulatory initiatives.

NRC Phase 2 Recommendations: Aftertreatment Program Activities

Committee Comment on 21CTP Responses

In general, the committee thought the progress was substantial and the effort should continue. The exception was a need for more work on characterizing PN emissions.

Findings and Recommendations: Aftertreatment Systems

Finding 3-6. The research agenda for 21CTP is focused on a wide diversity of heavy duty (HD) emissions control work. There are impressive fundamental studies on SCR catalysts, DPF fundamentals, low-temperature SCR and oxidation catalysts, passive NO_x adsorbers, multifunctional components, emissions measurement and modeling, system models, fuel effects, aging, and sensor development. Work is not continuing in 21CTP on lean-NO_x traps but has become part of the light-duty vehicle programs. These programs are delivering valuable results, but there are no program goals to guide future directions.

Recommendation 3-3. The Partnership should continue work on aftertreatment and emissions control, but the DOE should develop specific aftertreatment goals for the 21CTP. These goals will serve as a focal point for researchers to submit proposals and for the DOE to assess them.

Finding 3-7. Lacking are fundamental studies or even reported results on unregulated emissions, such as CH₄ and N₂O. Also lacking are projects or objectives aimed at post-2010 regulations, specifically supporting the CARB low-NO_x initiatives, in particular cold-start NO_x control using, for example, low-temperature NO_x adsorbers and SCR filters.

Recommendation 3-4. The Partnership should continue to fund work on improved SCR NO_x efficiency (mainly at low temperature, without compromising high-temperature efficiency) and aging and poisoning effects. California’s and, potentially, EPA’s move toward further HD NO_x reductions to meet National Ambient Air Quality Standards (NAAQS) for ozone will be critical. These new targets need to be set for the research efforts.

Recommendation 3-5. New fundamental emphasis on N₂O formation to support lower NO_x emissions should be added, as there is an apparent trade-off between low NO_x and higher N₂O caused by the need to inject more urea.

Finding 3-8. To achieve 50 percent BTE in the SuperTruck Program (Chapter 8), the engine compartment has limited space for the cooling system, the waste heat recovery system, and the aftertreatment system. The aftertreatment system volume, weight, and cost are important for the design of the engine compartment for trucks that are developed for 50-55 percent BTE.

Recommendation 3-6. Technologies such as an SCR catalyst on a DPF or others that have the potential to reduce the volume, weight, and cost of the aftertreatment system should be a part of the program to develop a 55 percent BTE engine.

Finding 3-9. OBD is a key industry need. It is a primary consideration in emissions control design and architecture and a major cost component. OBD technology is not available to meet the expected California low-NO_x regulations.

Recommendation 3-7. DOE should determine the gaps in OBD understanding and in sensor technology, especially to meet the tight California regulations, and should implement programs to help fill these gaps.

FUEL PROGRAMS

This review of fuel programs affecting the 21CTP begins where the NRC Phase 2 review finished (NRC, 2012). Some of the findings and recommendations regarding fuel technologies in the NRC Phase 2 report are still valid and will be briefly mentioned. New fuel issues, many reviewed in the 2013 21CTP Roadmap and Technical White Papers (21CTP, 2013), are described, and additional research is recommended.

The most significant change in the hydrocarbon petroleum resource pool since the NRC Phase 2 report has been the substantial increase in the supply of crude oil derived from directional drilling and hydraulic fracturing (“fracking”) (Harvey and Loder, 2013). The properties and characteristics of hydraulically fractured crude oil samples from shale are generally different than those of crude samples pumped from large pools or deposits of oil. Crude oil from shale tends to be lighter than crude from many other sources (GAO, 2014). The blending of light crude oil derived from fracking operations with heavy crude oil streams (such as from tar sands deposits) creates an unusual blend of hydrocarbon components (sometimes referred to as a “dumbbell” oil blend) that can be challenging for some refineries trying to produce a complete slate of fuel products (Gonzalez, 2014). Although crude oil from shale is increasing the national energy supply, its characteristics are more suited for producing gasoline rather than middle distillates such as diesel fuel. This could impact the properties of diesel fuel in the future as well as force refiners to make capital upgrades to their refinery operations (Gonzalez, 2014).

Efforts to produce greater amounts of biodiesel (fatty acid esters) and to create renewable diesel derived from biomass have increased modestly since the NRC Phase 2 review.⁷

The use of natural gas as a fuel for medium- and heavy-duty trucks is increasing slowly based mostly on increased gas supplies generated from new extraction techniques and the resulting lower fuel costs. A discussion of the pros and cons of natural gas as a transportation fuel was recently published by the NRC (2014). Natural gas has been suggested as a method to reduce transportation sources of greenhouse gases (GHGs), although this conclusion requires further validation.

Advanced Petroleum Fuels

The DOE has active research programs that address diesel fuel properties, whether they are petroleum-derived or not. As explained earlier in the discussion on engine systems research, cooperative work between the DOE and the CRC (2012) has created a well-characterized, petroleum-based fuel matrix called FACE. This fuel matrix is specifically designed so that “researchers evaluating advanced combustion systems may compare results from different laboratories using the same set (or sets) of petroleum fuels for consistency” (CRC, 2005). For diesel fuel, the matrix consists of nine fuel blends varying in cetane number, aromatic content, and T₉₀ values (temperature at which 90 percent of the fuel is distilled). A graphic depicting the matrix is shown in Figure 3-8.

The fuels described by this matrix are designed around the fuel properties and characteristics likely to affect advanced combustion system performance. They are not “an implied or explicit recommendation or endorsement for the adoption of any of these research fuels as implied or explicit fuel standards” (CRC, 2005). They do serve a valuable purpose, however, by providing a basis for comparison of test results from research programs intended to evaluate the performance of advanced combustion engine technology. The use of these fuels has already been described in some of the projects reviewed in the Engine Systems portion of this chapter and will be described further in some of the fuels projects.

Petroleum-based diesel fuel properties could become an issue in future years because of the production of greater amounts of light crude oils from fracking. As previously stated, crude oils from hydraulic fracturing processes contain significant amounts of highly volatile, low-molecular-weight hydrocarbons (GAO, 2014). When blended with other heavier crude sources either produced in or imported into the United States, the result is a crude oil blend with large amounts of light distillates and of heavy distillates but fewer components in the middle of the distillation range. Although

FIGURE 3-8 Fuels for advanced combustion engines (FACE) diesel fuel set. SOURCE: B. Zigler, “Fuels for Advanced Combustion Engines,” DOE Annual Merit Review FJ002, May 15, 2012. National Renewable Energy Laboratory.

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⁷ See biodiesel production statistics at http://www.biodiesel.org/production/production-statistics.

such crude blends can be handled within modern refineries, a potential impact could be a decline in middle-distillate yields (Gonzalez, 2014).

The United States has for many years been a large importer of crude oil, mainly to meet the needs of transportation. Recent increases in domestic production have largely alleviated the concerns over crude supplies (GAO, 2014). If the demand for diesel fuel continues to increase and demand for gasoline for light-duty vehicles decreases due to fuel economy and emissions regulations, an adequate diesel fuel supply may become the most important future transportation energy concern. Research targeted at utilizing renewable fuels in spark-ignition engines may not be as critical as that targeted at diesel engine fuel efficiency strategies and the use of biodiesel or renewable diesel fuel blending components in advanced combustion engines.

The cost of producing petroleum-based fuels and the price of commercial fuels at the pump reached new highs during the last decade. Today, due to greater crude production, fuel costs have dropped substantially. This is important to OEMs in determining the cost of new technology they would be willing to invest in to improve efficiency and reduce fuel consumption. It is also important in determining the extent to which alternative fuels will be economically competitive with petroleum-based fuels. If the cost of petroleum-based fuels remains low, and if alternative or renewable fuels are desired for reduced GHG emissions, the use of such alternative fuels will be realized only through application of regulatory initiatives.

Biofuels

For many years, biofuels have been promoted by some government agencies for four reasons:

1. To extend petroleum resources,
2. To reduce petroleum imports,
3. To reduce GHG emissions, and
4. To increase domestic jobs.

Given the increase in domestic oil and gas supplies in recent years, the first two justifications for greater biofuel generation and sale are much less significant than at the beginning of the twenty-first century, when future oil supplies were thought to be limited.

The biofuels industry has continued to grow since the NRC Phase 2 review, but the use of biofuels in commercial fuel formulations is still limited. DOE has contributed to the development of technology and processes for producing cellulosic ethanol and biodiesel fuels, with the ultimate goal of commercialization. Congress established the Renewable Fuel Standard (RFS) in 2007, which set a goal of using 36 billion gallons of biofuels per year by 2022. Congress has provided tax credits and incentives for biofuels production, including that of renewable, ester-based diesel fuels. These credits and incentives generally remain in effect. An NAS-NAE-NRC (2009) report concluded that sufficient resources for biomass were available in the United States, and that substantial amounts of biofuels could be produced by 2020.

Despite the plans for increased production promoted by federal agencies, the only significant source of biofuels today is corn-based ethanol. This ethanol is added to gasoline in the United States, mostly at a concentration of 10 percent, although the EPA in 2010 allowed as much as 15 percent ethanol in gasoline for use in 2007 and later-model-year, light-duty vehicles. In early 2011, the EPA expanded its waiver to allow up to 15 percent ethanol in gasoline used to fuel 2001 through 2006 model-year, light-duty vehicles. The EPA cannot force fuel stations to provide gasoline blends containing 15 percent ethanol without the approval of Congress, which at this time it does not have. The use of 15 percent ethanol has been opposed by automotive OEMs due to concerns over durability in engines designed for 10 percent ethanol in gasoline (Shepardson, 2010), and to date only limited amounts of gasoline containing 15 percent ethanol have been sold at U.S. commercial fuel pumps.

The commercial production of cellulosic-derived ethanol is only now beginning to be realized. Three companies, Abengoa, Poet, and DuPont, announced plans to produce ethanol from cellulosic materials in either 2014 or 2015 (Abengoa, 2014; Poet, 2014; DuPont, 2015). The combined production of denatured ethanol from these three plants could reach 81.6 million barrels per year (ca. 0.61 percent of total denatured ethanol consumption in 2014). Commercial production of ethanol derived from cellulose has been supported by DOE (2014).

The production of biodiesel (essentially fatty acid methyl ester [FAME] and other esters) and renewable diesel (a pyrolyzed/hydrotreated, biomass-derived feedstock used in refineries for diesel fuel production) has been minimal but continues to increase.⁸ In 2013, the EPA concluded that the industry was not going to be able to produce the amount of biofuels called for by the RFS (EPA, 2013). Thus, the total 2014 requirement for biofuel for use in transportation applications was temporarily set at 15.21 billion gallons per year (EPA, 2013). In 2013, ethanol production in the United States (virtually all corn-based) amounted to 13.31 billion gallons per year (RFA, 2014). Based on Energy Information Administration (EIA) estimates for U.S. gasoline consumption in 2013 of 135 billion gallons and distillate fuel consumption in 2013 of 58.7 billion gallons, this amount of ethanol is roughly equivalent to its use in gasoline at 10 percent (EIA, 2014b). By 2022, the RFS has a requirement for the use of 4 billion gallons of advanced biofuels, which can be just about any renewable fuel except corn-based ethanol. Even if all of this was biodiesel fuel, it would still meet only a relatively small percentage of diesel fuel demand.

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⁸ Ibid.

To meet future RFS requirements, advances in manufacturing processes and reductions in manufacturing costs are needed for ensuring growth in the use of biofuels. Looking ahead, biofuels for use in petroleum-based diesel fuel could be manufactured in one of two ways:

1. Make a biodiesel fuel, such as FAME or another ester, from a specific feedstock, such as soybeans, and blend it into existing diesel fuel.
2. Make a bio-based, renewable bio-crude oil by pyrolysis or hydrotreatment that can be used at a refinery in the production of conventional diesel fuel.

Much of the early effort to develop biofuels for blending with diesel fuel was for the development of ester-based fuels such as FAME, as described in the first option. The process for making simple, ester-based biofuels is well documented and has been in use for many years. In the biodiesel production process, triglyceride oils derived from biomass are reacted with methanol to produce a fatty acid alkyl ester and glycerin as a by-product. The quality of such biodiesel components is defined by ASTM standard D6751. These biofuels are now blended into diesel fuels in some regions of the United States and, to a greater extent, in Europe.

Significant commercial effort has been directed toward the production of renewable diesel fuels, as described by the second option, although such fuels are currently not much used in the United States (Peckham, 2014a). Renewable diesel fuel uses feedstocks from gasified biomass to generate a hydrocarbon stream that is processed at a refinery during the production of petroleum-based diesel fuel.

Renewable diesel fuel is viewed by the oil industry as a better option than biodiesel (Peckham, 2014a) for the following reasons:

1. It is all hydrocarbon and is chemically more like diesel fuel;
2. It is more compatible with diesel fuel infrastructure and engines than biodiesel and in many instances provides a fuel blend that meets ASTM D975 specifications; and
3. It avoids unwanted effects associated with ester-based biodiesel fuels (e.g., FAME), such as lower volumetric energy content, instability, hygroscopicity, injector fouling, and low-temperature operability, among others.

Alternative Fuels

One of DOE’s original 21CTP goals was to replace some of the petroleum fuels used for transportation with nonpetroleum-sourced alternatives. Other than ethanol from corn and natural gas, use of other alternative fuels has been limited. The status of ethanol use as an alternative fuel is discussed in the preceding section. A detailed review of the use of natural gas in medium- and heavy-duty trucks has been published by the NRC (2014). The reader is referred to this review for information on issues related to the use of natural gas.

In 2012 there were still only 127,000 natural gas vehicles (NGVs) of all classes in the United States, or 0.05 percent of the total vehicle population (NGV Global, 2012). Despite this small percentage, the EIA predicts that medium- and heavy-duty trucks will be the largest transportation consumer of natural gas by 2040. This natural gas consumption will most likely be divided between compressed natural gas (CNG)-fueled, medium-duty trucks and liquefied natural gas (LNG)-fueled, heavy-duty trucks. Even in 2040, however, the use of natural gas will represent only 3 percent of total transportation energy consumption (EIA, 2014b).

The NRC (2014) report provides a good explanation of the changes in the natural gas supply in the United States that are due to the development of new processes for fracturing shale deposits. Since the publication of that report, the recovery of natural gas has grown significantly, such that the United States is currently the world’s leading gas producer. In addition to there being greater amounts of natural gas available, this increased production is also being driven by potential GHG regulations. It has been estimated in some well-to-wheel (WTW) energy and emissions analyses that, even taking into account increased methane emissions from natural gas vehicles, total GHG emissions will be lower than from pure gasoline- or diesel-fueled vehicles (NRC, 2014). However, lower GHGs with use of natural gas will have to be balanced against the greater energy consumption that occurs due to lower engine efficiencies when using natural gas as a fuel.

Additional calculations are needed to demonstrate the GHG emissions reduction benefits and the drawbacks of new manufacturing facilities and technologies for production of liquid hydrocarbon fuels from natural gas. It is well known that large-scale gas-to-liquid (GTL) manufacturing plants are planned for the United States (Berman, 2014). In addition, new technology has been proposed and developed that uses mini gas-to-liquid processing equipment (Peckham, 2014b). Such equipment could be employed at stranded gas deposits for which there is no connection to a gas pipeline. The liquid fuel produced would be transported by truck, eliminating the need for gas pipeline construction. The resulting GTL fuel would be subsequently blended with conventional petroleum fuels at a refinery, creating a blend that meets commercial fuel standards. If commercially profitable, these mini GTL facilities could further expand the use of natural gas for the production of synthetic hydrocarbon fuels.

As pointed out in the NRC (2014) report, there is a need for developing lower cost, smaller natural gas fuel storage systems. A Class 8 natural gas truck can cost $50,000 to $100,000 more than its diesel fuel counterpart. The cost of installing a refueling facility is extra (the cost will depend on the number of trucks that must be refueled in a given time period). Much of the increased truck cost is associated

with the fuel storage system: high-pressure tanks for CNG or cryogenic tanks for LNG.

Biomass-derived dimethyl ether (DME) has received attention, especially in Europe, as a sulfur-free diesel fuel substitute because of its high cetane number (55) and very low emissions of PM, NO_x, and CO. This fuel would require minor engine and fuel system modifications, but would necessitate a dedicated infrastructure for production, distribution, and storage, which is expected to be a major hurdle for its commercialization in the United States.

Review of 21CTP Fuel Technology Objectives

In the NRC Phase 2 report, it was pointed out that DOE had established three different sets of goals for the fuels research program from 2008 to 2011 (NRC, 2012). It was further noted that changing goals during that period made it difficult to assess progress against those goals. In fairness, it must be said that significant fuel research has been conducted and much important information gained at the DOE laboratories and by academic institutions and industrial research facilities since 2010. It is not of value to recount past changes in goals for fuel research. Instead, it will be assumed that the goals identified in the 21CTP Roadmap and Technical White Papers published in 2013 accurately reflect the current technology goals for the program (21CTP, 2013).

In the 2013 Roadmap and Technical White Papers, three specific technology goals are listed under Engine Systems. Goals 1 and 2 have already been reviewed in the engine systems section of this chapter. Goal 3 (21CTP, 2013) is as follows:

Progress on fuel technology in order to meet Goal 3 is as follows: A series of FACE diesel fuels has been selected and defined in cooperation between DOE and the CRC. These fuels have a selection of specific physical and chemical properties (cetane number, aromatics content, and T₉₀) and are commercially available for laboratories to purchase for individual research projects. FACE fuels and other surrogate diesel fuels are being used in several DOE laboratory programs designed to quantify advanced combustion engine performance and efficiencies when using fuels having well-defined characteristics.

This most recent version of Goal 3 is unrealistic in its currently stated objective of identifying “essential” fuel properties given the ongoing research on a wide variety of different combustion strategies. The committee believes that identification of a range of fuel properties that could enhance the performance of advanced combustion modes, such as LTC, would be a more realistic objective. FACE provides researchers with the ability to perform experiments with fuels of known characteristics, having property ranges that are within a range of variations that might be seen in future fuels. This is superior to running specific blends of research-grade fuels that are not representative of what an engine will experience in the field.

Although not specified as goals for Engine Systems within the 21CTP Roadmap and Technical White Papers, it is important to note that the document also listed a number of needed fuel research efforts that would help the 21CTP meet its overall objectives. Some of these include the following (21CTP, 2013):

• Develop [a] fundamental understanding of fuel effects on in-cylinder combustion and emissions formation processes in advanced combustion regimes;
• Develop predictive tools that relate molecular structure to ignition behavior and heat release for fuels used in advanced combustion engines;
• Evaluate new fuels and fuel blends for efficiency, emissions, and operating stability with advanced combustion regimes;
• Evaluate the potential of reforming small amounts of fuel to generate additives that can be used to achieve fast control in LTC modes;
• Identify renewable and synthetic fuel blending components that provide enhanced efficiency, performance, and emissions characteristics; and
• Evaluate performance of traditional lubricant formulations in engines using advanced combustion regimes.

21CTP, DOE, and DOD Fuel Projects

The DOE provided the committee with a list of 22 DOE, DOD, and NSF research programs investigating advanced fuel technologies that the committee believes should be considered as part of the 21CTP. The fuel projects, which are listed in Table 3-6, amount to a total budget in 2014 of $7,669,000.

The fuel research projects identified as linked with the 21CTP span the gamut from fundamental research (analytic modeling and laboratory-scale experiments), to fired single-cylinder, to full-scale dynamometer engine tests. Many of the fuel projects have the objective of evaluating the effects of fuel composition (including both hydrocarbons and biofuels) on advanced combustion strategies and emissions control systems performance (McCormick and Ratcliff, 2014; Mueller, 2014; Kurtz, 2014; Szybist et al., 2014; Reitz, 2014; Toops et al., 2014b). For example, Mueller at SNL (Project FT004) has utilized FACE fuels, surrogate fuels, and other diesel fuels to improve understanding of fuel effects on advanced-mixing, controlled-combustion strategies such as leaner-lifted flame combustion (LLFC). Surrogate fuels are well-defined formulations of specific chemical compounds for which models can more easily be derived in order to

TABLE 3-6 Major 21CTP-Related Projects Funded in FY 2014 Addressing Advanced Fuels (federal dollars)

NOTE: Acronyms are defined in Appendix E. Some of the projects included in Table 3-6 for the fuels budget apply to both light- and heavy-duty vehicles. Dash denotes no funding. SOURCE: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.

describe combustion under different operating conditions. This work has led to the development of a new “soot diagnostic” (Vertical Sheet Laser Induced Incandescence of Soot, VLII) for measurement of fuel effects on in-cylinder soot distributions and for assessment of soot models (Mueller, 2014). In a related study, Kurtz at Ford (Project FT017) demonstrated that increasing oxygen content in the diesel fuel increased the flame lift-off length and led to less soot formation (Kurtz, 2014). McCormick and Ratcliff (2014) at NREL (Project FT003) are investigating the use of biofuels containing minimum amounts of oxygen as “drop-in,” nonpetroleum fuel components. Eight different oxygenates have been evaluated. Aromatic oxygenates were found to lower cetane number and increase premixed burn fractions, while di-isoamyl ether was found to raise diesel cetane number and reduce ignition delay and premixed burn fractions (McCormick and Ratcliff, 2014). At ORNL, Szybist et al. (2014) (FT008) are evaluating different biofuel blends in conventional spark ignition (SI), dilute SI, homogeneous charge compression ignition (HCCI), and reactivity controlled combustion ignition (RCCI) engines. In a downsized, downspeeded SI engine, a renewable super premium (RSP or E30) gasoline demonstrated improved efficiency relative to regular gasoline over limited operating cycles (the efficiency improvement outpaced the energy density loss). The RCCI operating range was expanded to 75 percent of its theoretical maximum while maintaining low soot and NO_x emissions when using the combination of B20 (20 percent biodiesel in petroleum diesel) and gasoline (Szybist et al., 2014). A research project at the University of Wisconsin partially funded by the DOE (FT015) is developing prototype light-duty and heavy-duty vehicles using RCCI engine technology employing a combination of gasoline and diesel fuel (Reitz, 2014). Toops et al. (2014b) (Project FT007) have investigated the effects of fuel and lubricant formulations on both gasoline and diesel emissions control system components. As a follow on to the work of Szybist et al. (2014), Toops and his team at ORNL have demonstrated that E30 ethanol/gasoline blends produce particulates with a higher reactivity (oxidize at lower temperatures) than regular gasoline in gasoline direct-injection (GDI) engines. The ORNL team is also developing accelerated laboratory diesel emissions durability tests in order to identify the effects of metals in biodiesel formulations on catalyst degradation. Currently, the focus is on creating a correlation between emissions control components that have been subjected to commercial long-term, heavy-duty service and those that have been subjected to severe laboratory tests (Toops et al., 2014b).

In addition to these experimental research programs, efforts are being conducted to develop comprehensive chemical kinetic mechanisms for petroleum-based and bio-derived fuels (Zigler, 2014; Som et al., 2014). For example, Som et al. at ANL (Project FT022) is using a three-component diesel surrogate fuel to develop models for biodiesel that predict both in-nozzle flow and spray characteristics, as well as combustion kinetics used in CFD simulations (Som et al., 2014). Zigler at NREL (Project FT002) has combined laboratory experiments with modeling efforts to identify combustion characteristics of specific fuel components and blends. This work has developed an ignition quality test (IQT) that allows the calculation of a derived cetane number (DCN) using as little as 25 ml of fuel. The IQT also provides data for calculation of Arrhenius parameters, used in combustion kinetics modeling. Importantly, the IQT is capable of measuring ignition performance and providing kinetic data for fuels ranging from gasoline to jet fuel to diesel to associated biofuels.

Based on the fuels project portfolio provided by the DOE, there is only one project that involves research on the development of natural gas engine technology. This project, conducted in cooperation with the South Coast Air Quality Management District (SCAQMD) and the California Energy Commission (CEC), was last funded in 2010. The committee received no update on the results or status of this program during any of its meetings.

Although the fuels research portfolio covers critical issues related to improving engine efficiency needed to meet 21CTP goals, the organization of DOE fuels projects relative to each other appears only loosely coordinated. Many useful fuel experiments are being conducted at different DOE laboratories, but the research is being conducted on a variety of advanced combustion engines using different fuels. It is not clear what the downselect process for focusing future (beyond 2015) engine/fuel research will be. How will DOE identify the most promising engine/fuel combinations for improving engine efficiency or reducing GHG emissions? How will DOE identify the most promising projects for future funding? Admittedly, some projects need to be completed before their full value is determined, but at this point the research path forward is unclear. Today, fuel projects seem to be generated by a bottom-up process based on recommendations of individual researchers at different laboratories. A top-down process via DOE management or peer review that identifies good options for commercial success would help focus limited resources on potential best outcomes.

The military fuels program has had a consistent set of objectives throughout the life of the 21CTP. Those objectives are to (1) minimize the number of fuel types that the military must purchase and transport, (2) minimize the amount of fuel used in operation through engine and vehicle efficiency improvements, and (3) increase the amount of non-petroleum-based fuels used in both tactical and combat applications. The military would prefer to use the same fuel (the most desired fuel is JP-8) in all of its vehicles. As described in the NRC Phase 2 report (NRC, 2012), the Army, through TARDEC, has the unique role of qualifying alternative fuels for use in tactical and combat vehicles having diesel engines.

The Army would like to use fewer petroleum-derived fuels, although there is a realization that it will be difficult to do so. It is exploring biodiesel fuels, but the lower energy

density of most biofuels is a drawback. The military has a rigorous procedure for qualifying alternative fuels. This procedure could prevent some bio-based fuels from being accepted based on technical specifications. However, it is possible that federal military fuel procurement regulations could be written to require the military to develop technologies that are compatible with bio-based fuels. For that reason, the military continues to conduct and support research projects (at national laboratories and universities) to develop advanced diesel engine technologies that deliver improved efficiency and vehicle range when using bio-based fuels.

The fuels portfolio in Table 3-6 includes five such research projects managed by TARDEC. Research topics include development of new methods for determining fuel bulk modulus, development of ignition models for heavy hydrocarbon fuels, and development of combustion models using surrogate fuels for alternative JP-8 fuel formulations. A new method for measuring bulk modulus is needed because this parameter can vary greatly between biofuel samples and hydrocarbon fuels, affecting high-pressure injector flows.

Response to Recommendations from the NRC Phase 2 Report

Committee Comment on Response to 3-4

The committee is satisfied with the total research effort directed at understanding the effects of petroleum-based fuels on advanced combustion technologies. However, at this time, the different research laboratories do not appear to have a coordinated research plan on how to identify the fuel properties that are most appropriate for the varied combustion strategies being investigated. Current research directions and test fuel formulations seem to be selected by individual laboratories without coordination.

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Committee Comment on Response to 3-6

Other than the development of a FACE fuels set, the committee is not aware of any other specific 21CTP fuels goals. In view of laboratories seeming to select the fuels for their individual research projects, it would benefit DOE to improve the coordination of fuel sets used by different research groups. In addition, specific combustion objectives should be assigned to each fuel set in order to determine the benefits that are available from various fuel compositions.

Findings and Recommendations: Future Fuel Research

Finding 3-10. A series of fuels for advanced combustion engines (FACE) and surrogates have been identified in cooperation between the DOE and the Coordinating Research Council (CRC). These fuels have specific physical and chemical properties and are being used in several advanced combustion research programs, including the evaluation of various LTC concepts (e.g., LLFC, RCCI), the development of CFD models for in-nozzle flow, spray formation, and combustion, and the development of new analytical techniques (e.g., IQT, VLII).

Finding 3-11. Currently, fuel projects appear to be generated by a bottoms-up process based on recommendations of individual researchers at different laboratories without guidance from DOE management on the practical ramifications of specific fuel choices or on the chances of commercial success.

Recommendation 3-8. The DOE should continue to explore how the United States might use its abundant petroleum, natural gas, and biofuel resources in the most efficient manner. Studies, some of which are under way that contribute to this objective, should strive to answer the following questions:

1. What fuel properties (e.g., ignition characteristics, volatility, composition) of diesel fuel and gasoline maximize the efficiency of various advanced combustion engines? FACE and a common set of surrogate fuels should be utilized by all DOE facilities involved in combustion research programs in order to provide consistent fuel characteristics when evaluating laboratory experiment and engine test results.
2. Based on well-to-tank analyses, what fuel properties and processing procedures result in the lowest GHG emissions for hydrocarbon-based and bio-based fuel components?

Finding 3-12. Goal 3 in the Engine Systems chapter of the 21CTP 2013 Roadmap and Technical White Papers identifies the objective of determining the essential fuel properties required to enable advanced combustion systems that can achieve 55 percent BTE. This 2014 goal as currently stated seems unrealistic to the committee. It suggests that there are specific fuel properties and values that will expand the oper-

ating range of advanced combustion strategies, such as various LTC concepts. The committee feels that the importance of fuel research is much broader than this. The FACE fuels provide researchers with the ability to perform experiments with fuels of known characteristics, having property ranges that are within a range of variations that might be seen in future fuels. This is superior to running specific blends of research-grade fuels that are not representative of what an engine will experience in the field. Using FACE fuels also helps with the kinetic model development being pursued in the surrogate fuel simulation program. Researchers can now test their advanced kinetic models against realistic, but known, fuels in real engines, an important step in developing simulation capabilities for predictive behavior. The committee believes a more detailed understanding of the impact of fuel properties on engine operation and potential facilitation of advanced combustion operation will also facilitate the high-level objective of maximizing the utility of our fossil fuels, thus reducing their use.

Recommendation 3-9. The Partnership should consider revising Goal 3 in its 2013 White Papers to make it more consistent with what the committee observes it is doing within the current fuel research programs—for example, facilitating the development of kinetic models for realistic fuels that could embody a range of properties and understandings of how fuel characteristics either probably, or even just possibly, will impact or facilitate current and potential combustion strategies. Also it is suggested that consideration should be given to whether enhanced understanding of the interplay between fuel characteristics and engine performance can suggest powertrain–fuel system combinations that further reduce fossil fuel consumption.

Finding 3-13. Despite past efforts to increase the use of renewable fuels, petroleum will remain the primary source for light-duty and heavy-duty vehicle fuel for the foreseeable future. U.S. gasoline demand is expected to decrease during the next 25 years, while diesel fuel demand is expected to grow. If regulators continue in their efforts to meet the Renewable Fuel Standard goals, production of biodiesel and renewable diesel will need to increase.

LUBRICANT PROGRAMS

Over the last 35 years, low-viscosity, low-friction engine oils, transmission fluids, and axle lubricants have contributed to improvements in light-duty vehicle fuel economy (Swed-berg, 2012). Owing to their higher loads and lower speeds, it is not clear whether similar efficiency gains attributable to lubricant formulations can be achieved in heavy-duty diesel operation, but it is important to conduct the research that will define the benefits of such lubricants. Although the DOE has sponsored research on new lubricant additive technologies for reducing friction and thus fuel consumption, most of this work has focused on light-duty vehicle applications.

Traditionally, lubricants for truck engines have been developed and qualified for commercial sale through the combined efforts of the American Petroleum Institute (API), the American Chemistry Council (ACC), the American Society for Testing and Materials (ASTM), and the Truck and Engine Manufacturers Association (EMA). These organizations have developed test methods and labelling that ensure that oils meeting engine manufacturers’ needs for durability, low emissions, and fuel efficiency are available in the U.S. market. The DOE has recently become active in developing new lubricant additive and base stock chemistries that might help in meeting the goals of the 21CTP. For example, it participated in the Collaborative Lubricating Oil Study on Emissions (CLOSE) project. Of particular concern in the development of new lubricant additives is any effect of sulfur from the engine oil (and the fuel), and any effect of phosphorus and ash from the engine oil on emissions control system performance, especially in regard to PM and NO_x reduction.

Relative to light-duty vehicles, not as much progress has been made in reducing friction through the use of advanced lubricants in heavy-duty vehicles, although low-friction, low-viscosity oils from the petroleum industry are being tested in the SuperTruck Program (see Chapter 8). Most commercial heavy-duty engine oils continue to be SAE 15W-40 viscosity grades. The use of these higher viscosity grades has generally been justified by the claim that greater viscosity provides better film thicknesses in heavily-loaded contacts within high-powered diesel engines.

Early industry tests have focused on improving MHDV truck fuel efficiency through the implementation of new, high-temperature, high-shear (HTHS) viscosity recommendations. HTHS viscosity specifications were introduced into the SAE J300 Engine Oil Classification in the 1980s in order to ensure that engine oil was viscous enough to protect heavily-loaded, fluid-film bearings. Tests with reduced HTHS viscosity oils instead of SAE 15W-40 oils have shown modest reductions in fuel consumption while other traditional additive components continue to protect durability and performance. Fuel consumption results are shown to be duty-cycle specific (NRC, 2012).

Review of 21CTP Lubricant Technology Objectives

As with the other goals related to fuel technologies, goals for improved lubricant technologies for the benefit of the 21CTP have changed over the years. The NRC Phase 2 report (2012) stated the following:

Recently, the 21CTP Roadmap and Technical White Papers (21CTP, 2013) stated in Goal 5 for Vehicle Power Demands that DOE’s objective is to “develop and demonstrate parasitic friction reduction technologies that reduce driveline losses by 50%, thereby improving Class 8 fuel efficiencies by 3%.” Based on experience in the light-duty vehicle industry beginning in the 1980s and until today, this is an ambitious but achievable target. If it is accepted that this statement of achievability for a lubricant goal reflects DOE’s current objective for the 21CTP, progress toward meeting this goal is described below.

A research portfolio consisting of projects whose objectives are the development of new friction-reducing/antiwear additive, base oil, and viscosity index technologies has been created. The projects are being conducted at the national laboratories and by universities and private companies. Recent results have shown promise in reducing friction in heavily-loaded laboratory contacts and in improving fuel economy in limited vehicle tests, but almost all of the results have been collected in light-duty vehicles, or under laboratory conditions designed to mimic light-duty service. Collaborations have been established between OEMs and oil and additive companies that are participating in the “SuperTruck” program, but no data on the specific benefits of the advanced lubricants used in the program have been provided to the committee.

As previously mentioned in the discussion of fuel technology, it is important to note that the 2013 Roadmap and Technical White Papers also lists needed lubricant and tribology research efforts that would help the 21CTP meet its overall objectives. These include the following:

• Evaluate performance of traditional lubricant formulations in engines using advanced combustion regimes.
• Determine tribological limits of current materials and sensors.

DOE and DOD Lubricant Programs

The 21CTP provided the committee with a list of 10 DOE and DOD projects related to the development of advanced lubricant technologies. The lubricant projects are listed in Table 3-7 and amount to a total budget in 2014 of $3,653,000 (see Appendix D).

The lubricant research projects identified as linked with the 21CTP also range from fundamental research (analytic modeling and laboratory-scale experiments), to single-cylinder engine tests, to full-scale dynamometer engine tests.

At ORNL, Toops et al. (2014b) and Qu et al. (2014a) are studying the use of ashless, ionic fluid, friction modifiers/antiwear additives in engine oils (Projects FT001 and FT014). The ionic fluid additive has been shown to reduce catalyst poisoning slightly relative to the commonest phosphorous-containing antiwear additive. In addition, this additive has demonstrated a 2 percent improvement in fuel economy relative to a commercial SAE 5W-30 engine oil in light-duty vehicle service. There are no data at this time from tests in heavy-duty vehicle service. This research project includes representatives of a major additive company who could help identify other commercial opportunities for this technology, such as use in axle lubricants.

Work at ANL (Erdemir, 2014) has focused on research using nanoparticles suspended in engine oils to reduce friction (Project FT018). Boron-containing additives have been the most effective. In low-speed, high-load diesel engine screening tests, boron-containing lubricants improved fuel economy 1.5 to 2.5 percent. Emissions catalyst poisoning tests need to be conducted.

Additional research (Projects FT021, VSS058) on advanced lubricants includes the development of low-friction, hard-surface coatings (Qu et al., 2014b; Ajayi et al., 2014). Further research results (preferably in heavy-duty engines) are needed to evaluate these lubricants more thoroughly.

The Army keeps many of its engines for 40 to 50 years, and so there is concern about the compatibility of newer fuels and lubricants in these engines. For example, diesel engine fuel pump and injector life can be an issue with low-lubricity fuels. Research on new technologies such as ashless antiwear and lubricity additives could provide oil and fuel formulations that are compatible not only with advanced engines but also with existing engines in operation today. For this reason, the Army, in its facilities at TARDEC, manages and conducts fundamental studies of lubricant additive technology.

Response to Recommendation from the NRC Phase 2 Report

TABLE 3-7 Major 21CTP-Related Projects Funded in FY 2014 Addressing Advanced Lubricants (Federal Dollars)

NOTE: Acronyms are defined in Appendix E. Some of the projects included in Table 3-7 for the fuels budget are applicable to both light- and heavy-duty vehicles. Dash denotes no funding. SOURCE: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.

Committee Comment on Response to 3-5

The committee supports DOE’s basic research efforts related to development of low-friction additive technology and concepts as long as they are targeted at improved fuel efficiency in medium- and heavy-duty driveline applications and if they are carried out in cooperation with commercial oil and representatives from the additive companies.

Findings and Recommendations: Future Lubricant Research

Finding 3-14. There is a DOE 21CTP lubricant goal, but the current lubricant research portfolio appears to focus more on light-duty vehicle applications than on heavy-duty powertrain applications. Since the evaluation of advanced lubricant technology in Class 8 trucks is only occurring in the SuperTruck program in cooperation with private oil and additive companies, it is not possible to quantitatively separate out lubricant benefits and judge progress against the 21CTP goal.

Recommendation 3-10. A greater portion of the laboratory lubricant development projects should be redirected at meeting the requirements and test conditions associated with heavy-duty truck use. Tests in HD vehicles or in full powertrain dynamometer tests should be conducted in order to verify friction reduction benefits of advanced lubricant technologies relative to conventional lubricants and to judge progress against the 21CTP goal. This work should be conducted in close coordination and involvement with OEMs and with companies in the additive and petroleum industry.

PROPULSION MATERIALS–MATERIALS PROCESSING

Current heavy-duty engines have demonstrated the long-term reliability and durability required for use in Class 8 trucks. The next generation of HD engines will pose new materials challenges that are being addressed in the 21CTP. HD engine development has as its objective to improve performance and engine efficiency. Furthermore, these engines

must be lightweight, cost-effective, and meet all emission requirements. The materials challenge includes the development of propulsion materials that can withstand the high temperatures and pressures found in the engine environment. Manufacturing and inspection methods are an integral part of materials development. The advanced materials must enable cost-effective fuel savings. Several DOE projects address the critical need for propulsion materials, motors, and components that meet the constraints for HD transportation applications. Given the long time needed for the identification, development, and implementation of new materials, continuity of R&D is essential. Work is under way at the national laboratories on new alloys and on overcoming the mechanical property limitations of materials at high cylinder pressures and temperatures (see Table 3.8).

High-temperature materials work at ORNL involves the development of exhaust valve materials with high fatigue life for use in advanced engines. Computational methods are being used to predict alloy compositions with desired properties, including oxidation resistance up to 900^oC. Other work at ORNL in advanced materials development for advanced turbocharger designs is under way. These materials have the high temperature capability and strength needed for sustained operation at high operating temperatures. The modification of surfaces is aimed at reducing friction between contacting surfaces in the engine. This work addresses the goal of 50 to 55 percent BTE.

PNNL work on materials for advanced diesel engines aims to develop and deploy engineered surfaces with improved thermal and mechanical properties using friction stir processing. To date, fatigue life has been improved by a factor of two. Materials projects at PNNL also include manufacturing technologies for high-power induction and permanent magnet motors. The goal is lower manufacturing cost and lighter weight assemblies. In other work, new aluminum alloy compositions are being developed with high strength at elevated temperatures.

The National Energy Technology Laboratory (NETL), together with Caterpillar, is exploring HD-high performance cast steels for crankshafts. Microstructure and processing parameters are being explored in an investigation of durability requirements. A related project has as its objective to improve component strength of new ferrous materials by 25 percent.

In summary, these materials projects address the following:

• Alloys for engines with improved strength, reduced friction, and better thermal and mechanical properties,
• Improved high-temperature performance for exhaust valve materials,
• Turbocharger designs,
• New cast steels for crankshafts,
• Alloy development for extrusions and forgings, and
• Permanent magnet electric motors.

It is beyond the scope of this report to review all projects in detail. However a few of the materials projects related to propulsion are summarized below.

ORNL Project PM053 (High Temperature Materials for High Efficiency Engines) began in September 2013 and is scheduled to end in August 2016. This project is 100 percent funded by DOE, and ORNL leads the project. Anticipated funding for FY 2014 is $200,000. This project has as its objective to develop cost-effective exhaust valve materials for use in advanced engines operating at temperatures up to 950^oC. Computational methods are being used to predict new alloy compositions with needed oxidation resistance, fatigue properties, and stability. Recently, the effect of composition on oxidation resistance at 800^oC was addressed and work is on track for evaluation of selected alloys up to 900^oC. Alloying elements that enable the desired microstructural characteristics are being identified for new Ni-based alloys. Current low Ni alloys do not have good strength at 950^oC, and alloys used in aerospace applications are expensive owing to both high Ni content and the use of expensive alloying elements. The goal of this work is to provide high cycle fatigue life comparable to that with the high Ni alloys but at lower Ni levels.

PNNL Project PM004 (Tailored Materials for Advanced CIDI Engines [through FY 2013]). This project, which began in FY 2008, is a CRADA with Caterpillar and PNNL. Its objective is to develop and deploy engineered surfaces via friction stir processing (FSP) in traditional engine materials and to develop FSP in aluminum. Treated engine materials exhibited better thermal and mechanical properties. Friction stir processing can selectively modify an area of a part for better properties. Project milestones reached include the demonstration of a twofold improvement in fatigue life and reduction in thermal crack initiation and growth. Results have been documented. Process parameters, prototype parts, and knowledge have been transferred to Caterpillar.

PNNL Project PM004 (Novel Manufacturing Technologies for High Power Induction and Permanent Magnet Electric Motors [FY 2014]). This project, which began in FY 2011, was scheduled to have ended in September 2014. It is a CRADA with General Motors and PNNL. The objective of the project is to develop and deploy high-power induction rotors and stators that are lightweight and less expensive to manufacture than current assemblies. The approach is to apply friction stir welding as a low-cost method to join the bars to the end caps. Process parameters are being developed. The microstructure and mechanical properties of Cu/Cu joints was examined. A welding fixture was developed for friction stir welding of Al and Cu rotor parts.

PNNL Project PM044 (High Temperature Aluminum Alloys). This project, which also began in 2011, is a CRADA between Cummins and PNNL. Its objective is to develop aluminum alloy compositions with high strength at elevated temperatures (300 MPa tensile strength at 300^oC) using a

TABLE 3-8 21CTP Projects Related to Propulsion Materials and Materials Processing and Federal Budgets (dollars)

NOTE: CAT, Caterpillar; CIDI, compression-ignition direct injection. Dash denotes no funding.

melt spinning process to produce flakes, which are then consolidated by extrusion. Laboratory-scale extrusion tooling was developed for use in consolidation and extrusion. The mechanical properties of the extrusions and forgings were evaluated. Test results on three alloy compositions showed that two compositions, (AFCT [Al-Fe-Cr/Ti] and AFM-11 [Al-Fe-Mn]) had higher tensile strengths at 300^oC than Al-8.5 Fe alloy. The AFM-11 alloy had a tensile strength exceeding 250 MPa. Full-scale components will be tested in the future.

ORNL Project PM057 (Applied ICME for New Propulsion Materials). This project, led by ORNL, began in FY 2013 and will run through FY 2017. The project makes use of integrated computational materials engineering (ICME) to address the need for more efficient, faster, and less expensive materials development for propulsion applications. The project is totally funded by the DOE. Funding received in FY 2013 was $70,000, and the FY 2014 budget is $580,000. Specific applications addressed are the development of ceramic perovskites composed of lead-zirconium-titanate (PZT). High-ZT thermoelectric materials are of interest for waste heat recovery and climate control; piezoelectrics for high-performance fuel injection; low-cost permanent magnets, eliminating rare earth elements for electric drive systems; and durable low-temperature catalysts for exhaust emission control that operate near 150°C. Progress reported to date includes the prediction of high-p-type thermoelectric performance in PbSe. Work is currently under way on first-principle exploration of alloys near PZT, and two alloys have been selected for further development. Hf₂Co₁₁B and Fe₅PB₂ were identified to be promising materials for permanent magnet applications. Work is progressing on a hydrothermally stable CuFe-SSZ-13 catalyst composition with good low temperature activity for NH₃-SCR.

NETL Project PM058 (HD-High Performance Cast Steels for Crankshafts). This project, led by Caterpillar,

started in March 2014, and the DOE budget for FYs 2014-2017 is $300,000. Partners include General Motors, ANL, Northwestern University, and the University of Iowa. The objective of the project is to develop cast steel alloys and processing techniques for high-performance crankshafts with as-cast properties of 800 MPa ultimate tensile strength and 615 MPa yield strength. ANL will apply high-energy x-ray imaging and diffraction techniques to correlate microstructure with processing parameters. Fatigue tests will be used to establish durability requirements.

NETL Project PM059 (Development of Advanced High Strength Cast Alloys for Heavy-Duty Engines). This project, led by Caterpillar, was started in December 2012 and is scheduled to end December 2016. Total project funding is $5.08 million, with a DOE share of $3.48 million and a contractor share of $1.6 million. The objective of this project is new high-strength ferrous materials with at least 25 percent improvement in component strength relative to components made with A842. At the same time, targets are set for cost that will speed the adoption of new materials. As of June 2014, 16 prototype casting samples had been designed and produced. Materials properties of prototype castings alloys are being evaluated. X-ray tomography was found to be capable of identifying graphite structures in the iron matrix, and fluorescence analysis provided chemical information. During FYs 2013-2014, work progressed on identifying and modeling critical mechanisms that govern microstructure development during cast iron solidification.

ORNL Project PM038 (Materials for Advanced Turbocharger Designs). This project began in September 2009 and was scheduled to end September 2014. The budget for FY 2014 was $150,000. This project is a CRADA with 50/50 cost sharing by DOE and Honeywell. The project supports the Advanced Combustion Engine goal for the 2015 commercial engine with a 20 percent improvement in efficiency over the 2009 baseline efficiency. Turbocharging improves fuel efficiency, but the higher temperatures (>750^oC, diesel; >950^oC, gasoline) exceed the strength and temperature capability of current materials. Turbocharger housing and other components with more temperature capability and strength are needed for higher sustained operating temperatures. The alloy being investigated is CF8C-Plus cast stainless steel, which has more strength than HK30Nb stainless alloy at 750^oC and is 33 percent less expensive. This alloy was commercialized by Caterpillar in 2006 for its Cat Regeneration System (CRS), used to regenerate the diesel particulate filter. Recent progress on this CRADA includes diesel engine exhaust testing of CF8C-Plus steel at 800^oC and evaluation of oxidation resistance of CF8C-Plus in diesel exhaust. The CRADA was not extended by DOE and Honeywell continued on its own.

ORNL Project PM007 (Friction and Wear Enhancement of Titanium Alloy Engine Components). This project started in October 2009 and had a project end date of September 2011. The project was funded by DOE at $350,000 per year for FYs 2010-2012. Informal collaborators on this project were Cummins, Greenleaf Corporation, and NASA Glenn Research Center. This project addressed the goal of 50 percent improvement in freight efficiency by substituting strong, durable corrosion-resistant alloys for steel components. Specifically, the goal was to increase the use of titanium alloys in friction-and-wear critical engine components such as connecting rods, valves and valve guides, pistons, movable vanes in turbochargers, and bushings in EGR systems. Initially, a test method was selected for baseline friction-and-wear tests, and reciprocating pin-on-flat tests were conducted on materials, coatings, and surface treatments in order to select materials/treatments for the second phase of this project. No information was available to the committee beyond the 2011 project review.

ORNL Project PM052 (Friction Reduction through Surface Modification). This project started in October 2010 and was scheduled to end September 2014. The total project funding was $1,135,000. The objective of the project was to improve the fuel efficiency of HD diesel-powered vehicles by reducing the friction between contacting surfaces of the engine. It is estimated that in an HD engine, 10-15 percent of energy is lost to parasitic friction and that a 20-40 percent friction reduction would improve fuel efficiency by 2-6 percent. The target components include piston rings, connecting rod ends bearings/bushings, and cam followers. The method for reducing friction was a combination of surface texturing and coating technology. Milestones reached are (1) a report was produced describing the durability test procedure to be used for textured surfaces, (2) studies were completed on the effects of texturing on friction in a reciprocating piston ring/liner configuration, (3) wear-resistant thin coatings for textured bearing surfaces were selected, and (4) friction test specimens of textured and coated specimens were obtained.

NETL Project PM059 (HD-Cast Fe Alloys for High PCP Engines). The goal of this project is to develop new high-strength ferrous alloys for enabling increased peak cylinder pressures for improved performance and efficiency of heavy-duty engines. The project uses an integrated computational materials engineering (ICME) approach to computationally engineer new material compositions and manufacturing processes to achieve improved material performance, with a goal of a 25 percent improvement in component strength relative to A842 compacted graphite iron. At the time of the committee’s meetings, the project, conducted with Caterpillar, had been under way for about a year, so it was not presented at the DOE 2014 AMR. It was presented at the DOE 2015 AMR, however. Accomplishments during the first year focused on establishing baselines for properties, structure, and machinability.

Response to Recommendation from the NRC Phase 2 Report

Committee Comment on Response to 3-10

The committee is satisfied with this response.

High Temperature Materials Laboratory

The High Temperature Materials Laboratory (HTML) at ORNL is no longer operating as a national user facility as a result of federal budget reductions. The facility remains available, however, for project work under a CRADA that provides cost-recovery. The NRC Phase 2 report noted that this laboratory is a valuable resource for materials research for 21CTP in view of its specialized instrumentation and professional expertise.

Response to Recommendation from the NRC Phase 2 Report

Committee Comment on Response to 3-11

The committee agrees the HTML is a valuable resource for industry collaboration. For future collaboration, the DOE needs to maintain the facility and associated expertise and to review whether the budget changes have affected the state-of-the-art of the HTML capabilities, including staff expertise.

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