Owing to time constraints for preparation of this report, the committee has not been able to conduct a comprehensive analysis of new technologies that would supplement those identified in the National Research Council (NRC) Phase One Report. This will be done in an expanded effort in 2014 to 2015 for the committee’s final report, which will include both a thorough update to the data for the Phase One Report technologies and the analysis of any additional new technologies that have emerged since that report’s preparation.
The National Highway Traffic Safety Administration (NHTSA) has said that whereas the Phase I Rule was informed by the off-the-shelf technologies in the NRC Phase One Report, the Phase II regulations will be informed by the NRC Phase Two Report on future and advanced technologies. To this end, NHTSA contracted with the Southwest Research Institute (SwRI) to conduct a multiyear study of fuel-efficiency technologies for medium- and heavy-duty vehicles (Classes 2b-8) in the years before and during the Phase II regulations’ time frame. The work scope has the following tasks: Task 1: program management; Task 2: literature review and summary tables; Task 3: augment understanding of MY11+ vehicle fleet baseline (engines compliant with 2010 EPA regulations); Task 4: technologies in the MY 2018 fleet; Task 5: technology analysis for Phase II; Task 6: cost-effectiveness analysis for Phase II; Task 7: evaluation of MD/HD fuel economy and emissions testing and simulation approaches; Task 8: technical support—presentations to National Academy of Sciences (NAS)/industry events. Three tasks are of particular interest: Task 4, technologies in the model year (MY) 2018 fleet; Task 5, analysis of potential technologies for Phase II; and Task 6, cost analysis for potential technologies in Phase II. Technologies that SwRI is studying are based on four engines:1
- Detroit Diesel DD15 14.8 L I6. Optimize turbocompound for cruise performance (sacrifice top-end performance); evaluate electrical turbocompound (decouple power turbine speed from crankshaft speed); remove turbocompound; explore asymmetric turbo concept of 2013 DD15; explore no exhaust gas reduction (EGR) potential, including higher turboefficiency; check lower back pressure and aftercooler pressure differentials; explore reduced parasitic power from water, oil, and fuel pumps; explore engine friction reduction; explore downsizing or downspeeding options, including higher peak cylinder pressure (PCP) if needed; add bottoming cycle; and explore variable valve timing.
- Cummins ISB 6.7 L I6. Explore no EGR potential, including higher turbo efficiency; check lower back pressure and aftercooler pressure drop; explore reduced parasitic power from water, oil, and fuel pumps; explore engine friction reduction; explore downsizing or downspeeding options, including higher peak cylinder pressure if needed; possible upsized version for lower Class 8 applications; explore reactivity controlled compression ignition with information provided by the University of Wisconsin; and explore variable valve timing.
- 6.2 liter port injected V-8. Explore variable valve lift; explore cylinder deactivation (four cylinder); add stoichiometric gasoline direct injection (GDI); add lean burn GDI with selective catalytic reduction (SCR); explore GDI with EGR (high-efficiency dilute gasoline
1 Thomas Reinhart, Southwest Research Institute, “Phase 2 MD/ HD Vehicle Fuel Efficiency Technology Study.” Presentation to the Committee on Technologies and Approaches to Reducing the Fuel Economy of Medium- and Heavy-Duty Vehicles, Phase Two. Washington, D.C. June 20, 2013.
engine [HEDGE]); engine downsizing/downspeeding covered by 3.5 v-6; explore friction mean effective pressure (FMEP) improvements.
- Turbo DI 3.5 V-6. Explore variable valve lift; explore cylinder deactivation (base engine only); add lean burn GDI with SCR (use experimental data for lean limit and heat release); explore GDI with EGR (HEDGE); engine downspeeding with increased brake mean effective pressure and PCP (4000 rated, 24 bar torque peak); explore FMEP improvements (baseline only); and explore turboefficiency improvement (baseline only).
Although final results from these tasks are still pending, it is anticipated that this study will refine and supplement the NRC Phase One Report findings and recommendations regarding power train and vehicle technologies as summarized in Figure 6-1 and Tables 6-18 and 6-19 of the Phase One Report.
The projections in Figure 6-1 and Tables 6-18 and 6-19 of the NRC Phase One Report were developed under contract by TIAX and reported to the committee in Assessment of Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles (TIAX, 2009). In that report TIAX qualified these results with the following statement:
It needs to be emphasized that our package results are very dependent on the vehicle’s duty cycle and as such should be viewed as averages for each truck segment. Further, although the data for this analysis were obtained for the specific truck segments and, in general, for typical duty cycles for these segments, detailed vehicle simulation modeling was not done to establish the fuel consumption benefit of combined fuel savings technologies for each duty cycle. Follow up work is needed to confirm not only the individual estimated benefits but also the packaged benefits.
Neither the NRC Phase One Report nor NHTSA’s Factors and Considerations for Establishing a Fuel Efficiency Regulatory Program for Commercial Medium- and Heavy-Duty Vehicles (2010) cited this important qualification.
Finding: There is a wide range of possible fuel consumption potentials for various technologies and, further, a high likelihood of interactions between the latter when applied in combination such as might impact the aggregate fuel consumption potential. There is a wide range of ways in which various technologies could reduce consumption. There is also a high likelihood that the technologies will interact when they are applied in combination to further reduce aggregate fuel consumption.
Recommendation 2.1: NHTSA should conduct detailed simulation modeling and physical testing of various logical technology combinations and use the results to guide the setting of Phase II regulations.
In establishing the stringency of Phase II regulations, careful evaluation of technology penetrations is necessary. While NHTSA said that the intent of the Phase I Rule was to base the technologies on off-the-shelf technologies, the new baseline for revising those regulations is technologies embodied in more current vehicles, which will include not only off-the-shelf technologies but also those future/ advanced technologies that will have penetrated the market by 2018. SwRI project Task 3, MY2011+ fleet baseline, should show new technology penetrations that could become an updated baseline from which the Phase II Rule can be projected, depending on its success in capturing advances in the 2014-2018 time frame.
Recommendation 2.2: NHTSA’s Phase II Rule should take the current and projected incremental fuel consumption reductions and penetration rates of the various technologies into careful consideration: These incremental reductions and penetration rates should be updated from those that were projected in the Phase I rulemaking. Furthermore, system interactions should be evaluated for the effect on the projected incremental reductions whenever combinations of technologies are considered.
NRC (2010), NHTSA (2010), and TIAX (2009) (the latter prepared for the NRC Phase One committee) all included extensive descriptions, evaluations, and projections for the various individual power train and vehicle technologies identified in the Phase One Report. The results were summarized in Tables II.C.1 through II.C.9 of NHTSA (2010) and were derived from TIAX (2009). Given that these estimates are now more than 4 years old, high priority should be given to determining current values for these technologies and for including any new technologies that have emerged in the interim. The SwRI study for NHTSA should provide meaningful updates to these estimates. Additionally, the committee has to date met with and heard presentations from 32 government agencies, nongovernment organizations, and companies that sell automotive subsystems, engines, transmissions, and vehicles in Class 2b through Class 8 (see Appendix C). These categories were represented by presentations from Daimler, Volvo, Navistar, Cummins, Westport, Eaton, General Motors (GM), Ford, and others. To augment these presentations to the full committee, small groups of committee members visited original equipment manufacturers (OEMs) at their facilities or had telephone conversations with them. These activities are ongoing as the need for information arises.
The costs of these various technologies are germane as well. In the process of assessing the cost of new technologies, the Regulatory Impact Analysis (EPA and NHTSA, 2011) presented cost estimates for selected technologies for MY2030 and MY2050 compared to the 2011 baseline cost (in additional U.S. dollars). The committee has asked OEMs to comment on the order of magnitude of these increases;
however, given the fast track for this first report, these comments are pending. Likewise, projections of cost per truck and annual costs based on truck sales to 2050 are still under deliberation.
The following paragraphs will reflect only new technologies, fuel consumption estimates, or other considerations that have been revealed to the committee to date as potentially available in the Phase II time frame. As in NRC (2010; especially on p. 4, Tables S-1 and S-2), the committee addresses the uncertainty inherent in these estimates by reporting a range of values for the percentage reduction in fuel consumption that might be attributed to the addition of a single technology. The committee also analyzes the sensitivity of these estimates to certain variables such as environmental temperature (e.g., cold-start conditions), vehicle duty cycle, and/or manufacturing tolerances, and notes the effect where it is significant. Further, as noted above and quoted from TIAX (2009), the simple method of aggregating the single technologies may provide a different result than what a specific combination of technologies would produce in a power train or whole vehicle as a system. This system-induced uncertainty must also be recognized and evaluated through either simulation or physical testing of technology combinations.
Among the new engine and vehicle technologies that have been introduced since the Phase One Report, the emergence of natural gas as a transportation fuel is of significance. In addition, the growing interest in dimethyl ether (DME) as a finished fuel and the availability of natural gas and related renewable and alternative feedstocks to produce DME justify a focused analysis of technologies for natural gas engines and for other related vehicles. The latter topic will be covered further in Chapter 6.
All the OEMs are embarked on developing the engine. Among the specifics they are addressing are the following:
- Turbocharging, including dual-stage turbocharging with intercooling, mechanical and electric turbocompounding, and advanced EGR cooling. No additional new technologies or estimates have been provided in the reviews to date.
- Electrification of engine accessories. Traditional belt- or gear-driven accessories can be converted to electric power. The fuel consumption reduction results from the fact that in an electric actuation some accessories (such as power steering and the air compressor) can be operated only when needed. Other accessories (such as the water pump or cooling fan) could be run at speeds independent of engine speed. Either of the two cases can reduce fuel consumption. Electrification of accessories provides a 3 to 5 percent fuel consumption reduction if applied as a package on a hybrid vehicle. This benefit is more effective in urban driving conditions and in short-haul use; line-haul applications will benefit less. Vehicle and engine manufacturers of Class 2 through Class 7 vehicles report that electrical power steering is already in place and undergoing a global migration.
- Reduction of engine friction. Engine friction reduction has been pursued continuously by manufacturers through careful design and selection of advanced materials. Further efforts to make reductions face the added challenge of avoiding issues with durability and poorer performance. In the recent past, attention was given to using thinner lubricants; lower viscosity oil such as 10W30 was tested as a replacement for the standard 15W40 oil. It has now been confirmed by testing that a further reduction of 1 to 1.5 percent in fuel consumption may be obtained with thinner oils once durability has been confirmed. Thermostatic control of oil cooler—a solution used selectively in the past—can maximize lubricant performance over a broad temperature range. Some testing has reported a reduction in fuel consumption closer to 2 percent. The effect is more pronounced for cold starts and low-load operation. The introduction of greater volumes of synthetic base stocks will allow the evaluation and possible use of even lower viscosity oil formulations such as 5W30 and 0W30. In combination with advanced friction modifiers and viscosity improver additives, this could provide additional fuel efficiency. The amount of improvement, durability considerations, and penetration expectations will be evaluated and considered for the committee’s second report, due in 2016.
- Improvement of diesel exhaust particulate matter (PM) control using a diesel particulate filter (DPF) with a catalyst coating. The use of a DPF can degrade the fuel efficiency of the engine owing to exhaust flow restriction and pressure buildup in the system or the need for additional fuel to maintain the operation of the DPF. PM is collected in the DPF and disposed of periodically, either by combustion when the temperature is high during the normal cycle of operation or by injecting diesel fuel into the exhaust upstream of the DPF at light-load engine operation. A diesel oxidation catalyst oxidizes the fuel and generates the heat that regenerates the DPF in some manufacturers’ emission solutions. The current state of technology for DPFs is such that the additional fuel used ranges from 0 to 4 percent2 due to the fuel used for regeneration and the increased back pressure over the duty cycle.
- Improvement of diesel exhaust catalytic system efficiencies using selective catalytic reduction (SCR). Control of nitrogen oxide (NOx) has been accomplished with
cooled EGR and an SCR catalyst. The SCR catalyst uses the injection of a urea solution, diesel emission fluid (DEF), for converting NOx into nonharmful compounds. The infrastructure buildup for SCR/DEF was a significant challenge before 2010; however, the technology solution was ready for the 2010 federal NOx standards. This use of DEF is calculated as the equivalent fuel for consideration of the total fuel used. The 2010 emission standards for NOx required the use of SCR, but most manufacturers reduced the amount of EGR used and thereby improved the fuel efficiency of the engine (6.5 percent).3 The net reduction in fuel consumption (engine efficiency minus DEF usage) is 2 to 4 percent.4,5 This was one of the few heavy-duty emission control technologies in history that simultaneously enabled increased efficiency and reduced emissions. Encouraging new catalyst technology directions employing nanoscale catalytic materials on inert substrates are under investigation and will be evaluated by the committee in its second report.
At present, the above systems for NOx and PM control are working satisfactorily. Small improvements continue to be achieved, but the technology has attained maturity, and the fuel efficiency penalty may stabilize at about 3-4 percent for the entire system or about 2 percent for the PM control. These figures should be checked again as part of discussions with OEMs for the final report of the committee.
- Improvement in thermal efficiency of the diesel cycle in real operating conditions and with real engines (rather than in a controlled laboratory prototype). The challenge of improving thermal efficiency of the diesel cycle has been an active topic for research for several years. In a laboratory environment and under very controlled conditions, researchers can reach a thermal efficiency of 50 percent. They achieved this by simultaneous improvement of the compression ratio, expansion ratio, combustion chamber architecture, injection timing, injection pressure, rate shaping, air: fuel ratio control, air/fuel mixing, etc. All these measures contribute to a higher combustion temperature, which is good for lower fuel consumption, but they also increase NOx emissions, which is not good. It is expected that fuel injection may evolve further so that injection pressures that were as high as 2,300 bar in 2010 may increase to 3,000 bar by 2015 and perhaps to 4,000 bar by 2020. Moreover, new injection techniques may emerge (such as supercritical injection) and piezoelectric nozzle use may increase. A reduction of up to 6 percent in fuel consumption may be realizable. Also, if real-time combustion control becomes available with start of combustion sensors, then an additional 1 to 4 percent reduction in fuel consumption can be expected.
- The use of alternative combustion processes such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), and low-temperature combustion (LTC), even if in some limited operational range, for emission reduction. In search of improved cycle efficiency and, especially, generation of very low NOx levels, several combustion processes have been researched, such as HCCI, PCCI, and LTC. Some success has been obtained, but many challenges remain, especially in control over the entire range of engine operation. In the interim, approaches that provide partial operation of the engine in alternative modes are under investigation or have been demonstrated. Reactivity-controlled compression ignition (RCCI) has been shown to offer better controllability of premixed-type combustion using two fuels of different ignition properties. It is under investigation by a number of organizations.
- Improved efficiency of the driveline and improved system integration using strategies that enable the engine to operate at higher drive-cycle efficiency. Several technologies are worthy of mention. One is waste heat recovery. Cummins’ Supertruck demonstration with integrated bottoming cycle has achieved ~50 percent on-road efficiency. For Class 2b vehicles, the potential for 10-speed automatic transmissions with approximately 1 percent fuel consumption improvement compared to current 6-speed automatics has been identified by one OEM, GM. Cost and availability have not been provided, and it has been classified as High Development Risk. Another transmission manufacturer, Eaton, has shown a dual-clutch automatic transmission for line haul and vocational applications that reduces or eliminates power interruption during shifts. Allison has introduced a new 10-speed automatic transmission with a measured improvement in fuel economy compared to manual and AMT transmissions in Class 8 day cab vehicles.
- Hybrid power trains, including regenerative braking, engine downsizing, engine shut-off, enabling electrification accessories, plug-in hybrids, etc. No additional new hybrid systems have been identified in the reviews to date. However, given the high duty-cycle dependency, energy storage methods, costs, and relatively large potential fuel consumption reductions projected across most vehicle classes, NHTSA should form a study focused in this area to identify current realistic penetration rates and appropriate simulation and test methodologies to determine the resulting potential for fuel consumption reduction. Several manufacturers pointed out that with the ever more rapid rates at which new energy sources and new energy storage technolo-
3 W. Addy Majewski, SCR Systems for Mobil Engines, Dieselnet. com.
5 NRC (2010).
gies are being adopted, the points of regulation and the certification methodologies need to be examined and potentially modified to more accurately evaluate and credit this trend. Improvements to be evaluated included propulsion system dynamometer certification instead of engine-only certification; more emphasis on transients in modeling, simulation, and testing; and standards and certification only at the vehicle level.
The following technologies involving the other components of the vehicle are addressed by the OEMs as identified in the Phase One Report:
- Aerodynamic losses at high vehicle speed; improvements critical for vehicle aerodynamic optimization. No additional new technologies have been identified to date. Two truck OEMs (Daimler6 and Navistar7) have indicated that alternatives to coast-down testing should be considered, such as full-scale and scaled-down wind tunnel testing and computational fluid dynamics (CFD) analysis. They also indicated that aerodynamic bins should be based on wind-averaged drag rather than zero-degree-yaw drag. Daimler also suggested that greater accuracy would result by narrowing the Phase I Rule’s aerodynamic bins and increasing the number of bins by three.
- Implementation of aerodynamic features; barriers to implementation; cost and robustness at low speeds. No additional new technologies have been identified to date, but continued development has yielded more robust aerodynamic trailer skirts.
- Rolling resistance. The rolling resistance accounts for about 30 percent of the power to move a line-haul truck on level roads and at highway speeds. Reductions in the coefficient of rolling resistance of tires have been enabled both by development of new tire designs for standard width tires and the introduction of wide-base single tires (WBSTs). This technology allows the replacement of two conventional dual tires with a single new-generation wide tire; the coefficient of rolling resistance can be lowered from between 5 and 8 kg/ton to 4 or 5 kg/ton. Real-world testing and modeling have estimated almost a 10 percent improvement in fuel economy from this technology. In addition, some earlier studies by the Environmental Protection Agency (EPA) have also demonstrated reduction in oxides of nitrogen (Bachman et al., 2005). It is to be noted that the tire resistance is also influenced by tire wear (tread depth), by drive cycle, and by load.
Optimizing tire performance for a particular use is challenging because the numerous requirements are sometimes met by contradictory tire characteristics. It might therefore be impossible to have low-rolling-resistance tires for all vehicular applications. Fleets generally recycle partially worn tires by moving them from drive axles to the trailer, resulting in a less than optimum total vehicle package.
WBSTs provide a weight saving compared with dual tires of about 340 kg per five-axle combination tractor-trailer rig. This allows an increase in payload capacity, and it can improve freight efficiency. Despite these advantages, the adoption of WBST is limited owing to concerns about the occurrence of flats; stability and safety of the vehicle in the event of tire failure; availability of replacement tires; and the damage to roads caused by tire failure. Future discussions and test experience may show whether the effect of tire failure on safety has been overstated due to insufficient real data. At least one analysis (TIAX, 2009) believes that by 2016, the new tire technology applied to more axles may bring about a reduction in fuel consumption of about 11 percent in long-haul trucks.
- Vehicle mass; vehicle lightweighting. The truck weight impacts the power needed to move the vehicle through rolling resistance, climbing grades, and accelerations. Use of lightweight materials and structures, such as cab structures, wheels, fifth wheel, bell-housing, etc., have contributed to reducing weight in tractors; additionally, aluminum composite panels have reduced the weight of trailers. A barrier to further reduction is the higher cost of light materials. Lightweighting is simultaneously balanced by the increase in vehicle mass needed to accommodate additional systems and equipment, such as new emission control equipment, aerodynamic improvement equipment, waste heat recovery, and hybrid components. No additional new technologies have been identified to date.
Bachman, L., A. Erb, and C. Bynum. 2005. Effect of single wide tires and trailer aerodynamics on fuel consumption and NOx emissions of Class 8 line-haul tractor-trailers. SAE Paper 2005-01-3551. Warrendale, Pa.: SAE International.
EPA and NHTSA. 2011. Final Rulemaking to Establish GHG Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles: Regulatory Impact Analysis. EPA-420-R-11-901. Washington, D.C.: August.
National Highway Traffic Safety Administration (NHTSA). 2010. “Factors and considerations for establishing a fuel efficiency regulatory program for commercial medium- and heavy-duty vehicles.” DOT HS 811 XXX. http://www.nhtsa.gov/staticfiles/rulemaking/pdf/cafe/NHTSA_Study_Trucks.pdf.
6 Mike Christianson, Daimler Trucks North America, “OEM experience with GHG Phase I and recommendations for Phase II,” Presentation to the committee, June 20, 2013.
7 Greg Fadler, Navistar, Inc., “Navistar fuel economy and emissions,” Presentation to the committee, March 20, 2013.
National Research Council (NRC). 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, D.C.: The National Academies Press.
TIAX. 2009. Assessment of Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles. Report prepared for the National Academy of Sciences by TIAX LLC. Cupertino, Calif. July 31.