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3 Vehicle Subsystems This chapter discusses the vehicle systems technology areas that the Part- nership is addressing in its research and development (R&D) programs, which include the following: (1) advanced combustion, emission control, and fuels for internal combustion engines (ICEs); (2) fuel cells; (3) hydrogen storage onboard a vehicle; (4) electrochemical energy storage or technologies for storing elec- tricity onboard a vehicle; (5) electrical propulsion systems; and (6) materials for reducing the weight of a vehicle. The reader is referred to the presentations from the Partnership to the National Research Council’s (NRC’s) Committee on Review of the U.S. DRIVE Research Program, Phase 4, on the various techni- cal areas (Appendix D provides a list of the presentations to the committee at its meetings). The presentations can all be found in the project’s Public Access File, available through the National Academies Public Access Records Office. Chapter 4 addresses issues associated with hydrogen, electricity, biomass-based fuels, and natural gas. ADVANCED COMBUSTION ENGINES, EMISSION CONTROL, AND HYDROCARBON FUELS Introduction and Background It will take decades to develop and integrate non-internal combustion engine propulsion systems into becoming a significant fraction of the total U.S. mobility fleet. The internal combustion engine will be the dominant power plant for mobil- ity systems for at least the next 20 to 30 years (NRC, 2008, 2010). Consequently it is important to maintain a dedicated effort directed at ICE improvement within the U.S. DRIVE research portfolio. 53
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54 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP Furthermore, there is reason for optimism that the drive-cycle-based effi- ciency of ICEs can be improved, both through engine-based advancements and through hybridization, such that the fuel consumption of engine-powered vehicles can be significantly reduced. Also, the engine has a sophisticated and mature manufacturing basis and is capable of using a range of fuels, from petroleum to liquid-based biofuels to gaseous fuels, derived from a variety of feedstocks. Liquid fuels offer the attractive characteristic of having very high energy per unit of mass and energy per unit of volume. This characteristic facilitates long-range and/or sustained high-power-output vehicle operation. There will be, for many decades, applications for which the ICE-powered vehicle is the best choice. Life-cycle analyses reported in the literature, such as that shown in Fig- ure 3-1, suggest that total greenhouse gas (GHG) emissions for future high- technology ICE-powered vehicles1 will be made competitive with non-ICE- powered vehicles on a basis of total GHG life-cycle emissions, while still meeting stringent air quality regulations (Weiss et al., 2000; Bandivadekar et al., 2008). Uncertainty bars in Figure 3-1 denote well-to-tank GHG emissions for electric- ity generated from coal (upper bound) and natural gas (lower bound). For the well-to-tank GHG emissions from hydrogen fuel cell vehicles (HFCVs; shown as “FCV” in Figure 3-1), it is assumed that the hydrogen fuel is steam-reformed from natural gas at distributed locations and compressed to 10,000 psi. The advanced combustion and emission control (ACEC) technical team of U.S. DRIVE is the Partnership’s technical interface with the research commu- nity’s activities in advanced combustion and emission control. The goals, tech- nical targets, and program structure of the ACEC technical team build on those from the FreedomCAR and Fuel Partnership, which in turn built on the goals and targets from the Partnership for a New Generation of Vehicles (PNGV). For the FreedomCAR program, the advanced combustion and emission control targets and results were as follows:2 • Peak engine brake thermal efficiency (BTE) of 45 percent — his BTE was demonstrated with a light-duty diesel engine and an T H2-fueled ICE. • Oxides of nitrogen (NOx) and particulate matter (PM) emissions for light-duty diesel engines at Tier 2 Bin 5 (T2B5) standards — welve vehicle models that met this target were commercially avail- T able in the 2012 model year (MY). 1 Hybrid electric vehicles and plug-in hybrid electric vehicles are included in this classification because the engine still plays a major role as the energy converter between the fuel energy and work delivered to the wheels. 2 R. Peterson, General Motors, and K. Howden, Department of Energy, “Advanced Combustion and Emission Control Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
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VEHICLE SUBSYSTEMS 55 FIGURE 3-1 Predicted comparative total greenhouse gas emissions for current spark ignition engines (SIEs) and potential 2035 propulsion systems. NOTE: Acronyms are defined in Appendix E. SOURCE: Bandivadekar et al. (2008). • Power-train cost of $30/kW — his cost target guidance and status are currently under evaluation by T U.S. DRIVE. To push past the targets of the FreedomCAR and Fuel Partnership, the U.S. DRIVE Partnership addressed three engine technology pathways: (1) hybrid optimized (low-level power density), (2) naturally aspirated (mid-level power density), and (3) downsized and boosted (high-level power density); it identified engine efficiency metrics at three load conditions: peak efficiency; 2-bar brake mean effective pressure (BMEP)—2,000 revolutions per minute (rpm); and 20 percent of peak load—2,000 rpm. The specific 2020 stretch targets were set relative to 2010 MY engines for each technology pathway. Table 3-1 shows a compilation of these targets for each engine technology pathway for each of the three metric conditions. Standard fuels, either gasoline or diesel, are considered in specifying the performance metrics. For each of the three pathways being pursued to achieve the targets shown in Table 3-1, the fundamental approach and issues being addressed are these: 1. High-efficiency combustion with low engine-out emissions — Low-temperature combustion (LTC)
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56 TABLE 3-1 Advanced Combustion and Emission Control Efficiency Baselines (2010) and Stretch Targets (2020) 2010 Baselines 2020 Stretch Targets Efficiencya Efficiencya Efficiencyc @ 2-bar @ 20% of @ 2-bar Efficiencyc Peak BMEP and Peak Load Peak BMEP @ 20% of Peak Efficiency 2,000 rpm and 2,000 rpm Peak Loadb Efficiency and 2,000 Load and Technology Pathway Fuel (%) (%) (%) at 2,000 rpm (%)c rpm (%) 2,000 rpm (%) Hybrid application Gasoline 38 25 25 9.3 46 30 30 Naturally aspirated Gasoline 36 23 23 10.7 43 28 28 Downsized boosted Gasoline 37 22 29 19 44 27 35 Diesel 40 26 32 21 48 31 38 aEntries in percent brake thermal efficiency (BTE). bEntries in bar of brake mean effective pressure (BMEP). cEntries in percent BTE that are equal to 1.2 times the corresponding baseline BTE. SOURCE: R. Peterson, General Motors, and K. Howden, Department of Energy, “Advanced Combustion and Emission Control Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C. REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP
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VEHICLE SUBSYSTEMS 57 — Dilute spark-ignited combustion — Clean diesel 2. Improved efficiency with waste energy recovery — Solid-state and mechanical approaches — Improved air handling and lubricants 3. Efficient aftertreatment systems that reduce the energy penalty and meet emissions regulations — NOx, PM, hydrocarbons (HC), and carbon monoxide (CO) At first glance the above list of technology pathways appears to focus on development-type issues that would best be addressed by industry as part of product development. However, the barriers to achieving the targets given above are fundamental understandings of the controlling phenomena for each pathway, and this is the focus of the U.S. DRIVE activities. The optimization of the interaction among the following is very complicated: the ambient condi- tions; the details of the gas exchange processes (intake and exhaust processes, exhaust gas recirculation [EGR], boost, intercooling, manifold geometry, valv- ing events, etc.); the in-cylinder processes (injection characteristics, in-cylinder flow, combustion chamber geometry, fuel chemistry, etc.); and the exhaust-gas aftertreatment system (PM traps, NOx reduction systems, CO and HC oxida- tion systems, etc.) for minimum fuel consumption while meeting emissions standards. To address these challenges, industry uses analysis-led design, in which computational fluid dynamics (CFD) is used to predict the optimum combinations of power-train system control parameters for each engine operat- ing regime. This process is only as good as the accuracy and fidelity of the CFD pro- grams being used. Consequently, the lack of a detailed fundamental under- standing of the various thermo-fluid-chemical processes and their incorporation into CFD submodels is a barrier to further engine system optimization. Certain aspects of the challenges that industry must deal with are not understood at this time: for example, there is no accepted explanation for how lubricating oil is involved in the particulate formation processes within the engine cylinder. This is a relevant example of the importance of a lack of fundamental understanding, because higher-efficiency engines will rely on controlled air-fuel heterogeneity within the cylinder, which can lead to significant nanoparticle formation. Lack of understanding of the detailed processes occurring in the combustion chamber, like the particulate formation, subsequently impedes the optimization of engine performance through simulation. The engine combustion and emission research community is collaborating with industry to address these fundamental issues through experiment and simu- lation. To best duplicate the conditions in which to probe a deeper fundamental understanding of these phenomena, researchers perform experiments and simula- tions in representative engine geometries under real operating conditions.
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58 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP The primary framework through which the U.S. DRIVE ACEC technical team engages with research activities on combustion and emission controls is through the U.S. Department of Energy’s (DOE’s) Office of Vehicle Technologies Program (VTP). This office supports fundamental research in combustion, energy recovery, and aftertreatment performance. Within these programs there is partici- pation from industry, DOE national laboratories (Argonne National Laboratory [ANL], the Sandia National Laboratories [SNL] Combustion Research Facility, Oak Ridge National Laboratory [ORNL], Pacific Northwest National Laboratory [PNNL], Lawrence Livermore National Laboratory [LLNL], and Los Alamos National Laboratory [LANL]), and universities. DOE’s vision of the collaborative activities between national laboratories, universities, and industry is a progression from fundamental to applied research to technology maturation and deployment. Fundamental R&D is the focus of activities at the following: • Sandia National Laboratories — .g., Combustion Research Facility (lean-burn, LTC, advanced direct E injection) • Pacific Northwest National Laboratory — E.g., catalyst characterization (NOx and PM control) • Argonne National Laboratory — E.g., x-ray fuel spray characterization • Lawrence Livermore National Laboratory — E.g., chemical kinetics models (LTC and emissions) • Los Alamos National Laboratory — E.g., CFD modeling of combustion (KIVA code development) • Universities — Complementary research The fundamental to applied bridging R&D is performed at the following: • Oak Ridge National Laboratory — E.g., experiments and simulation of engines and emission control systems (bench-scale to fully integrated systems) • Argonne National Laboratory — E.g., H2-fueled ICE, fuel-injector design Finally, competitively awarded cost-shared industry R&D is done by the following: • Automotive and engine companies and suppliers — E.g., engine systems and enabling technologies (sensors, variable valve actuation, waste heat recovery)
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VEHICLE SUBSYSTEMS 59 The advanced combustion and emissions control program is well managed. The organizational structure of its activities involves memoranda of understanding between companies and government laboratories. It is usual for individual projects to include one or more of the national laboratories, a university, and an industrial partner. To ensure relevance, industry cofunding or matching is often required. In addition to the regular research meetings within a specific project, two formal research reviews are held each year, one at the Sandia Combustion Research Facility in Livermore, California, and one at the U.S. Council for Automotive Research (USCAR) in Southfield, Michigan. The researchers also participate in the DOE Annual Merit Review. Additional avenues for technical interchange are promoted through CLEERS (Crosscut Lean Exhaust Emission Reduction Simulation) and the Engine Com- bustion Network (ECN). CLEERS sponsors monthly teleconferences and an annual workshop to pro- mote the development of improved computational tools for simulating realistic full-system performance of lean-burn diesel/gasoline engine and associated emis- sion control systems. This activity helps in the development of emission control models that are integrated into vehicle simulations for drive-cycle analysis within the vehicle systems and analysis technical team (VSATT). The ECN supports a website and teleconferences to share and leverage research between experimenters and modelers on direct-injection fuel sprays and combustion. Overview of Technologies Being Investigated To implement new combustion strategies, effective exhaust-gas energy recov- ery, and aftertreatment systems that promote efficient engine operation, the air handling, combustion, and exhaust subsystem must be optimized as a system. Such optimization requires advanced computational fluid dynamics. It is now common that the design of a new power-train system is led by CFD. To extract increasingly better performance from the power train requires more accurate and detailed computational models. These models are developed through the coupling of fundamental experiments and computational submodel development. This is the interface at which the U.S. DRIVE effort is focused. In the area of high-efficiency combustion, the emphasis continues to be on low-temperature combustion. LTC is in essence controlled knock, and it relies on the auto-ignition chemistry of the fuel. Regardless of the fuel, the underlying approach to achieving acceptable LTC is the same. One wants to get the fuel vaporized and partially mixed with the cylinder gases such that when the auto- ignition chemistry reaches the point of ignition, the energy release is volumetric. Furthermore there needs to be sufficient inhomogeneity of the mixture within the combustion chamber that the entire mixture does not auto-ignite all at once, which would lead to excessive rates of pressure rise. This inhomogeneity can be in
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60 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP temperature, air-fuel ratio, or degree to which the local mixtures have kinetically traversed their auto-ignition pathway. If this is achieved, the engine efficiency is higher and the in-cylinder emissions are very low. The approach taken to control LTC will be dependent on the fuel type—gasoline-like, diesel-like, or dual fuels— and the load demanded of the engine. Since the NRC (2010) Phase 3 review of the FreedomCAR and Fuel Partnership carried out in 2009, five new combustion projects have been started to address these challenges. Regardless of how efficient the engine is, there will always be some usable energy in the exhaust that leaves the cylinder. As the engine efficiency gets higher, the usable energy in the exhaust gets smaller. Thermodynamically, it is known that as the portion of recoverable energy in the exhaust decreases, the efficiency of an exhaust-gas energy recovery system also decreases. However, in the quest to maximize engine efficiency, gains can still be made by the inclusion of exhaust-gas energy recovery systems. This imposes challenging constraints on the cost-benefit assessment of implementing energy recovery systems in the exhaust, and on maintaining a highly efficient exhaust-gas aftertreatment system. The fundamental research being pursued on exhaust-gas energy recovery within the ACEC technical team is to develop energy recovery systems that maximize the conversion of usable exhaust energy in ways that are economically viable. Research programs addressing exhaust-gas energy recovery involve elec- tricity generation with thermoelectrics, as well as more efficient turbomachinery and air handling. In addition, work is being supported on advanced lubricants, improved friction management, and materials for higher operating pressures and temperatures. Within the aftertreatment research programs, there are activities on devel- oping efficient catalysts that operate at lower exhaust temperature, improved NOx and PM aftertreatment systems, reducing the platinum group metal (PGM) requirement for the aftertreatment systems, and combining multiple aftertreatment systems into a single unit. The predictive capabilities of the current CFD programs are good. The simulation code used most widely at this time is KIVA III, developed by DOE. KIVA is an open-source-code program, which allows researchers to incorporate new understanding directly into the code for any aspect of the thermophysical processes occurring within the engine. For example, improved kinetic schemes for different fuel types or new submodels that more accurately represent liquid fuel-combustion chamber surface interactions can be implemented into the code and then exercised for more detailed predictions of combustion results. How- ever, KIVA III is more than 12 years old and lacks important, modern numerical technologies such as parallel computing and using an object-oriented structure. Having an up-to-date, open-source CFD program for researchers to use is a criti- cal aspect of achieving the improvement potential of the ICE and aftertreatment power trains.
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VEHICLE SUBSYSTEMS 61 The DOE is supporting work on a new version of the code, KIVA IV. To date the code has not been widely adopted. Discussions of committee members3 with academic users led to a list of possible reasons for the code not being widely adopted: • A code with KIVA IV’s level of physics and geometry (engines) needs to be modular and needs to have a data structure that is object-oriented. • The current effort allocated does not appear to provide the level of development support required for doing an acceptable job—an increased effort was suggested by academic users and submodel developers. • Code development for KIVA needs to be strongly tied to the activities of its “customers,” which are predominantly the universities where the advanced submodels are being developed and implemented. • Intellectual property (IP) issues associated with the code and submodels may be jeopardizing the open-source designation. If this key element is lost, the university following could disappear, which seems to be happening. Perhaps if a more active interface could be established between researchers working on the code development, university and research groups developing submodels, and industry partners, who will be the ultimate users of the code, the adaptation of the new code could be expedited. The energy companies continue to be engaged, and the program of Fuels for Advanced Combustion Engines (FACE), organized under the Coordinating Research Council (CRC), is supplying an important database for quantifying the impact of fuel characteristics on engine emission processes and alternative combustion process facilitation. In response to questions from the committee, U.S. DRIVE Partnership offi- cials commented that natural gas is not included in the Partnership’s technical scope. The committee believes that in light of the increased supply of natural gas and the high interest in using it to displace petroleum, an assessment should be made of whether natural gas is in any way an enabler for achieving U.S. DRIVE goals. For example, does natural gas facilitate the advanced combustion modes under investigation within U.S. DRIVE? The ACEC technical team’s responses to the recommendation of the previous review were good. The team is continuing to look for opportunities to enhance collaboration and has a program in KIVA code development. As discussed above, the committee believes that the KIVA code development effort could be improved. The ACEC technical team is making more use of the vehicle simulation that is being developed by the VSATT, and although it is not engaged in biofuels research, the team is aware of activities in the field. Also, the approach being 3 In particular, David Foster, committee member, had discussions with academic users.
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62 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP FIGURE 3-2 Department of Energy advanced combustion engine research and develop- ment (R&D) funding—FY 2010 to FY 2012. SOURCE: R. Peterson, General Motors, and K. Howden, Department of Energy, “Advanced Combustion and Emission Control Techni- cal Team,” presentation to the committee, January 26, 2012, Washington, D.C. taken within the ACEC technical team’s programs in developing kinetic models for combustion process simulation is compatible with the inclusion of compo- sitional changes that could occur to the fuel when biomass-derived compounds are blended with the fuel. Funding Even though the U.S. DRIVE Partnership’s ACEC technical team does not exercise control over a budget, it did offer to the committee an overview of the DOE funding within the advanced combustion and emission control programs for FY 2010 through FY 2012 (see Figure 3-2). Within the scope of the U.S. DRIVE goals, the work allocation for the continued development of the ICE and vehicle electrification seems appropriate.
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VEHICLE SUBSYSTEMS 63 Accomplishments This section presents a summary of accomplishments related to R&D activi- ties in the areas of advanced combustion, emission control, and fuels for internal combustion engines.4 Low-temperature combustion has proven to be an effective means of improv- ing closed-cycle efficiency and reducing the formation of NO x and particulates. By reducing the formation of NOx, both the cost and the complexity of additional aftertreatment can be reduced. The benefits of LTC are known, and include dra- matic reductions in the formation of NOx. However, controlling the in-cylinder processes leading to successful LTC operation is a challenge. The ACEC technical team has demonstrated a number of successes both in the control of LTC and in expanding its operational range within the engine duty cycle. One example of this success is a project at ANL where researchers were able to use 87 research octane number (RON) gasoline in a 1.9-liter turbocharged engine while retaining a full load range and diesel levels of efficiency with sub- stantially reduced NOx. The Sandia National Laboratories achieved indicated thermal efficiencies as high as 48 percent by using partial fuel stratification in a boosted homogeneous charge compression ignition (HCCI) engine. The ORNL has a project using E85 (a mixture of 85 percent ethanol and 15 percent gasoline) in a spark-assisted HCCI engine. A 17 percent increase in indicated thermal efficiency was achieved as compared to that of gasoline and over a wide range of loads. The use of two fuels, while adding some complexities and costs, also adds to the capabilities of controlling combustion and emissions. Reactivity controlled compression ignition (RCCI) engines involve the in-cylinder blending of two fuels with differing reactivity in order to tailor the reactivity of the fuel charge. Researchers at ORNL and the University of Wisconsin have used a diesel/gasoline multicylinder engine RCCI to demonstrate efficiencies up to 5 percent greater than diesel efficiencies. To better understand how dual fuels provide the benefits, fuel mixing and RCCI combustion were imaged from inside an optical engine by researchers at SNL and the University of Wisconsin. In other combustion research approaches, researchers from ANL, SNL, and the Ford Motor Company, using advanced direct injection of hydrogen, were able to achieve 45.5 percent peak brake thermal efficiency of a hydrogen-fueled ICE. Further, it is expected that minimal exhaust aftertreatment will be required to meet stringent emission goals. The researchers were also able to demonstrate a part-load efficiency of 31 percent while meeting T2B5 emissions standards. 4A full summary of accomplishments can be found in U.S. DRIVE Highlights of Technical Accomplishments: 2011, available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/ 2011_usdrive_accomplishments_rpt.pdf.
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VEHICLE SUBSYSTEMS 101 in this program; however, there is no significant effort to benchmark the target improvements of these projects over inverters employed in production vehicles that use electric propulsion. A proposed project is investigating the use of the same power switching devices for both the charger and the inverter. AC Propulsion is already marketing such a system, and it is being used in the Tesla and BMW Mini electric vehicles. It is hoped that the proposed project endeavors to improve on these production systems. Electric Motors The cost of rare earths used for permanent magnets has increased substan- tially, some by as much as an order of magnitude,25 in the past few years, and the Partnership has initiated projects to develop magnets without, or with a minimum of, rare earths. Extensive research on this subject is being done at the national laboratories. It is too early to evaluate the results, but this activity should be encouraged. Recently Mitsubishi has claimed success with magnet alloys with 1 to 4 percent rare-earth content with performance comparable to the magnets in the Prius, which contain approximately 10 percent rare-earth. 26 There is also a need for improved soft magnetic materials. Soft magnetic materials, which are used in motors, inductors, and transformers with higher per- meability, high flux density, and low loss, are needed. The standard for decades has been high-silicon steel with a maximum of 4 percent Si. More recently a Japanese company27 has developed a new process for making 6.5 percent Si, which will have lower loss but perhaps lower peak flux density. The suitability of this development needs to be determined. The program is also investigating new permanent-magnet motor designs. A possible design uses open slots to facilitate the insertion of formed coils, reduc- ing costs and reducing resistance loss but increasing eddy current losses on the magnets. It is hoped that this and other such projects bring about improvements over production motors used in hybrid vehicles on the road. In the Phase 3 report (NRC, 2010), it was recommended that induction motors for electric propulsion be investigated. Several hybrid vehicles on the road, such as the GM Buick LaCrosse, Tesla, and BMW, are using induction motors. Thus it may be worthwhile to com- pare induction and permanent-magnet motors to determine the relative efficiency and cost trade-offs for the two systems. Switched reluctance motors are also being investigated; however, acoustical noise continues to be an issue with this design. 25 See, for example, http://www.ft.com/intl/cms/s/0/751cab5a-87b8-11e0-a6de-00144feabdc0.html #axzz28AaO9ofv. 26 SAE, 2012, Powertrain Electric Motors Symposium for Electric and Hybrid Vehicles (April 20, 2012). 27 JFE Steel Hibiya Kokusai Building, 2-3 Uchisaiwaicho 2-chome, Chiyodaku, Tokyo 100-0011, Japan; see http://www.jfe-steel.co.jp/en/.
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102 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP On the other hand, ASEA-Brown Boveri claims that a synchronous reluctance motor has a better efficiency than an induction motor at smaller sizes. Thermal Management Heat removal from the silicon chip is a key determinant of the efficiency and size of the power electronics; thus thermal management plays an important role in meeting the program targets. Furthermore, matching differential expan- sion between the silicon chip and the (typically) aluminum heat sink is a tough problem, especially over the temperature range of –40°C to 200°C. There are many ways to minimize the thermal resistance from the silicon to the heat sink. One alternative is to use only aluminum and no copper plates to remove the heat. Other techniques consist of using direct sintering or double-sided cooling. The Oak Ridge National Laboratory claims to build a small, high-efficiency, planar bonded power electronic module for improved thermal management (Olszewski, 2011).28 A study to evaluate and compare the various alternative techniques and their relative merit to production units would be appropriate. The Nissan Leaf battery is air cooled, and other vehicles use liquid cooling. For example, the Volt uses a 50/50 mix of ethylene glycol for cooling the battery and possibly the inverter, whereas other vehicles use transformer oil. Traction Drive System The emphasis on the traction drive system in this program seems to be on components rather than on investigating the traction drive as a system. In fact, a thorough systems analysis of the traction drive may result in more optimized targets for the necessary components. Such an analysis is highly encouraged. For example, it may be possible to trade off the cost of improving the motor efficiency versus increased battery cost. The electric motor efficiency is targeted to be 95 percent or higher over a range of torque of 20 to 100 percent and over speeds of 10 to 100 percent. Such high efficiency over such a wide range of load seems overly ambitious. It may be more cost-effective to improve the battery performance by 2 percent compared to the cost of raising the drive efficiency from 93 percent to 95 percent. Also, there seems to be little work on “less costly mild hybrids.” Recently GM started selling the Buick LaCrosse Hybrid (Hawkins et al., 2012) with great improvements in the Environmental Protection Agency’s fuel economy (in miles per gallon) ratings.29 This remarkable result was achieved by a systems approach in which hybridization includes aggressive fuel cutoff during decelerations and stop-start. 28J. Czubay, General Motors, and S. Rogers, Department of Energy, “Electrical and Electronics Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C. 29 See http://www.fueleconomy.gov/feg/hybridCompare.jsp.
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VEHICLE SUBSYSTEMS 103 Significant Barriers and Issues Although electric machines and power electronics have been developed for many years for a variety of commercial applications, there are significant barriers to their utilization in electric drive vehicles, including BEVs, HEVs, PHEVs, and HFCVs. Barriers include inadequate efficiency and inadequate volumetric and gravimetric power density, and, most importantly, excessive costs. As discussed, a significant issue with this program is a lack of a thorough systems analysis of the complete traction drive system. Such an analysis not only would guide the program to which activity will provide the best results, but also would provide more optimized targets for efficiency, weight, volume, and cost for the various components constituting the system. Ideally, this should also include the battery, fuel cell, and internal combustion engine, so that the whole system can be optimized, and would involve separate analysis and targets for HEVs, PHEVs, BEVs, and HFCVs. As noted, significant improvements in various components and systems are being made at the national laboratories in this program. However, not much of this effort is finding its way to commercial applications. Also, establishing a supplier base for the large number of components involved in building an electrical drive system is warranted. Response to Recommendations from Phase 3 Review NRC Phase 3 Recommendation 3-19. The Partnership should continue to focus on activities to reduce the cost, size, and losses in the power electronics and electrical machines. [NRC, 2010, p. 105.] U.S. DRIVE seems to have pursued this recommendation. Prime examples are the GM, Delphi, and GE contracts that have improved on the state of the art. NRC Phase 3 Recommendation 3-20. The Partnership should conduct a project to evaluate the effect of battery charging on lithium-ion battery packs as a function of the cell chemistries, cell geometries, and configurations in the pack; battery string voltages; and numbers of parallel strings. A standard- ized method for these evaluations should be developed to ensure the safety of battery packs during vehicle operation as well as during plug-in charging. [NRC, 2010, p. 105.] The committee believes that this recommendation needs more attention. There is no evidence that the Partnership considered how high-rate charging affects the life of the battery.30 This issue needs to be addressed together with the 30 The following inaccurate and factually wrong sentence was removed from the report: “It is particularly surprising that nothing seems to have been done regarding safety even after the fires developed on the Volt in mid-2011.”
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104 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP electrochemical energy storage team and affects not only the charging regimen but also the monitoring and equalizing of the voltage of the cells. The role of the electrical and electronics technical team would be to specify the charging rates; presumably it can meet the need. Lithium-ion batteries have a history of causing fires in several instances. In addition to safety, there is a need to worry about bat- tery life, especially with “fast charging” at 440 V. The committee believes that continued work in this area is important and that the U.S. DRIVE Partnership should revisit Phase 3 (NRC, 2010), Recommendation 3-20. NRC Phase 3 Recommendation 3-21. The Partnership should consider conducting a project to investigate induction motors as replacements for the permanent-magnet motors now almost universally used for electric propul- sion. [NRC, 2010, p. 105.] U.S. DRIVE seems to have relied on preliminary findings from an ongoing DOE motor assessment indicating that induction motors will not meet its targets.31 This is interesting in that a mild hybrid vehicle (2012 Buick LaCrosse using the eAssist mild hybrid system) on sale by one of the Partnership’s partners demon- strated great improvement in fuel consumption, as discussed above. Clearly other factors contributed, but induction motors will meet some of the targets. Also, one of the new partners, Tesla, uses an induction motor in its vehicles. BMW also uses induction motors in some of its BEVs. Appropriateness of Federal Funding There is tremendous interest in electric propulsion worldwide, and a great deal of money is spent on improving the state of the art. However, HFCVs, BEVs, PHEVs, and even HEVs are unlikely to capture a significant share of the market unless dramatic improvements take place in all elements of the drivetrain. In addi- tion to the battery and fuel cell systems, which are discussed in other sections of this report, the cost, volume, and weight of power electronics and motors need significant breakthroughs. The Partnership is focusing on these three areas, which are interdependent. For example, better cooling of electronics reduces not only cost but also volume and weight; integrating the motor and electronics reduces not only cost but also volume; replacing rare-earth magnet materials has the potential of significantly reducing cost, although volume and weight may go up. Most of the funding goes to national laboratories, which will produce fresh thinking that would complement industry efforts, while the Partnership combines the best thinking of both. The fact that the electric propulsion components are used for all types of electric drive vehicles makes this a very strategically attractive R&D 31 J. Czubay, General Motors, and S. Rogers, Department of Energy, “Electrical and Electronics Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
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VEHICLE SUBSYSTEMS 105 investment and, in the committee’s view, the government has an appropriate role in helping with the introduction of electric propulsion and providing the United States with leadership. Recommendations Recommendation 3-14. The U.S. DRIVE Partnership should leverage the vari- ous investigations on wide-band-gap materials such as silicon carbide (SiC) and should determine how best to utilize these in power electronics for vehicular applications. Recommendation 3-15. The U.S. DRIVE Partnership should determine the potential and limitations of designing motors with permanent-magnet materials using less rare earth metal. Recommendation 3-16. The U.S. DRIVE Partnership should make a comprehen- sive assessment of the various methods available (some of these are discussed in the section titled “Thermal Management” in this chapter) to reduce the thermal resistance between the chip and the heat sink and establish their relative value to existing techniques in production vehicles. MATERIALS Goals and Challenges A critical component of any automotive manufacturer’s strategy to reduce fuel consumption and meet increasingly stringent Corporate Average Fuel Econ- omy (CAFE) standards and greenhouse gas emissions requirements is to reduce vehicle weight. For example, DOE has estimated that a 10 percent reduction in vehicle weight can result in up to a 6 to 8 percent improvement in fuel economy. Consequently, the U.S. DRIVE materials technical team (MTT), like the Freedom- CAR and Fuel Partnership before it, has adopted a stretch goal of 50 percent reduction in vehicle weight (versus 2002 comparable vehicles) with equal afford- ability (emphasis added). Previous committees (NRC, 2008, 2010) found this goal unrealistic, and it remains so today. Nevertheless, reducing vehicle weight is important, and doing so at the least incremental cost, while challenging, is worthy of pursuit, since achieving the 50 percent goal would result in up to a 35 percent fuel economy improvement. The DOE has developed a roadmap for a 30 percent weight reduction by 2025, which, if achieved, would result in up to a 21 percent fuel economy improvement. One factor that potentially assists with the task of major weight reductions is that of mass decompounding. That is, a reduction of weight in basic vehicle structure permits secondary weight reduction in brakes, suspension, power
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106 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP train, and other components. The materials technical team has estimated that each 1.0 lb of primary weight reduction may enable 1.0 to 1.5 lb of secondary weight reduction, provided that the entire vehicle can be redesigned to capture this opportunity. Nevertheless, large-scale weight reduction is an extremely challenging task, particularly since the addition of enhanced fuel-efficiency systems such as electrification results in the opposite effect, namely, mass compounding. Broadly speaking, there are three obstacles to achieving the Partnership’s stated stretch goals regarding vehicle weight: increasing vehicle content, main- taining structural integrity, and managing cost. • A 2011 Massachusetts Institute of Technology study (Zoepf, 2011) found that average passenger-car weight had increased by greater than 11 percent, or 160 kg, since 1990, despite the base car weight remain- ing unchanged. The entire weight increase was attributable to increas- ing comfort and convenience content and to added safety features and requirements. The pressure to keep adding feature content and more safety features will undoubtedly continue, in conflict with the need to reduce weight. Furthermore, the enhanced electrification of vehicles, while improving inherent fuel efficiency, adds considerable mass in bat- teries, motors, electronics, cooling, and so on, which must all be offset, including the mass compounding effect noted above, to yield the greatest fuel consumption benefits. • Compliance with the full suite of Federal Motor Vehicle Safety Standards provides confidence in the overall safety performance of a vehicle, but it becomes increasingly challenging as weight is reduced. This has led to increased use of sophisticated structural analysis tools and demand for stronger, lighter materials such as high-strength steels and carbon fiber. This trend can only accelerate in the future. • Cost is arguably the greatest challenge of the three: a detailed analy- sis in the NRC (2010) Phase 3 report illustrated both the high cost of weight reduction and the extent to which the reduction in fuel con- sumption can offset part of the cost to the ultimate consumer. However, the offset in fuel cost is only a fraction of the material cost penalty, and furthermore, much of the proverbial “low hanging fruit” has been harvested already. In light of these challenges, having the Partnership’s activities focused as they are on enabling advanced high-strength lightweight materials and reduc- ing their cost appears to be appropriate, even if the ultimate stretch goal is unrealistic.
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VEHICLE SUBSYSTEMS 107 Achievements In the materials area, the Partnership listed eight areas of major achievement in its presentations to the committee on January 26, 2012.32 These were as follows: • Completed design and manufacturability assessment of a magnesium front-end structure. • Completed design, tooling, fabrication, and testing of a one-piece com- posite underbody, saving 11.3 kg. • Optimized engineering and manufacturing processes for advanced high- strength steel (AHSS). • Developed a process for warm forming of aluminum and magnesium sheet. • Enhanced the formability of aluminum at room temperature. • Demonstrated a conversion technique for low-cost textile precursor for carbon fiber. • Improved performance of AHSS welds. • Developed a unique process for producing low-cost highly ductile mag- nesium sheet. Response to Recommendations from the Phase 3 Review Three recommendations on materials were made in the NRC Phase 3 report (NRC, 2010, pp. 108-109). The Partnership responses are shown below as “Updates.” NRC Phase 3 Recommendation 3-22. The materials technical team should develop a systems-analysis methodology to determine the currently most cost-effective way for achieving a 50 percent weight reduction for hybrid and fuel cell vehicles. The materials team needs to evaluate how the cost penalty changes as a function of the percent weight reduction, assuming that the most effective mix of materials is used at each step in the weight-reduction process. The analysis should be updated on a regular basis as the cost struc- tures change as a result of process research breakthroughs and commercial developments. [NRC, 2010, p. 108.] Updates: DOE FY 2011 solicitation results for the multimaterial vehicle car (50 percent lighter than a midsized vehicle, design, build, and validate): • Award to Vehma (Magna International)—project started in November 2011. 32 M. Zaluzec, Ford Motor Company, and C. Schutte, Department of Energy, “Materials Technical Team (MTT),” presentation to the committee, January 26, 2012, Washington, D.C.
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108 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP • Cost analysis for multimaterial vehicle with a systematic approach is in process at the Oak Ridge National Laboratory. NRC Phase 3 Recommendation 3-23. The magnesium castings study is completed, and no further technical effort is anticipated by the Partnership as recommended in the Phase 2 report. However, magnesium castings should be considered in completing the cost reduction recommendations listed above. [NRC, 2010, p. 109.] Updates: • DOE award to MOxST, Inc., for a clean and low-cost domestic supply of magnesium (Mg). If successful, this technology will introduce a lower- cost feedstock for alloy production and die casting. • DOE award to United States Automotive Materials Partnership (USAMP) on Magnesium Intensive Front End, which includes a focus on the char- acterization, optimization, and production of Mg die cast structural components. • Cooperative Research and Development Agreement project involving the Pacific Northwest National Laboratory, Ford Motor Company, University of Michigan, and MagTech (die casting supplier) to develop and vali- date mechanistic-based ductility models for Mg die castings. This will provide a better understanding of how die-casting characteristics affect ductility, in turn providing insight for methods to improve ductility. NRC Phase 3 Recommendation 3-24. Methods for the recycling of carbon- reinforced composites need to be developed. [NRC, 2010, p. 109.] Updates: DOE cofunding of Small Business Innovation Research work with Materials Innovation Technologies (Fletcher, North Carolina) to research low- cost carbon-fiber composite manufacturing using recycled aerospace carbon-fiber. Other global recycling efforts identified are as follows: • Nottingham University, United Kingdom: Fluidised Bed, Supercritical Fluids, Microwave; • Adherent Technologies, New Mexico, United States: Batch Thermo- chemical; • Valley Stade Consortium, Germany: Batch Pyrolysis; • Wells Specialty Products, Texas, United States: Fluidized Bed; • Ruag, Switzerland; • Firebird Advanced Materials, North Carolina, United States: Microwave; and • Milled Carbon, United Kingdom: Continuous Pyrolysis.
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VEHICLE SUBSYSTEMS 109 Discussion and Recommendations As noted earlier, weight reduction is a crucial part of any balanced approach to achieving aggressive fuel consumption targets and will undoubtedly entail enhanced computational methods and widespread materials substitution. The work being performed under the auspices of the Partnership appears to be properly focused on relevant initiatives. Although these initiatives appear relevant, the committee questions whether they all satisfy the criteria of high-risk, precompetitive research judged appropri- ate for federal involvement. Competition has raged among the steel, aluminum, and composites automotive supply base for many years in an effort to achieve low-cost weight reduction via materials substitution, and the aluminum, magne- sium, high-strength steel, and composites content of production vehicles has been steadily rising for more than 20 years. Furthermore, numerous vehicle demonstra- tion projects have been conducted in the past, both by materials trade associations and by industry consortia, some of which were sponsored by DOE. As noted in Chapter 2, the committee applauds the appointment by each tech- nical team of an associate member. However, the MTT has selected as its associ- ate member a manufacturer of aluminum truck bodies; although the company no doubt is competent, this selection would seem to add little in the area of greatest need, namely, long-term high-risk research into low-cost lightweight alternative materials. It might be productive for MTT to consider adding another associate member with this type of expertise. Phase 3 Recommendation 3-22 emphasized the need for systems analysis focusing on the most cost-effective way to achieve a 50 percent weight reduction. While the analytical approach in process at ORNL is responsive to that task, it is less clear what value the $10 million award (over 4 years) to Vehma to build another prototype multimaterial vehicle offers, especially considering that the award abstract does not even mention cost. Phase 3 Recommendation 3-23 reiterated the Phase 2 recommendation (NRC, 2008, p. 9) and essentially anticipated no further work on magnesium, other than inclusion in the analytical optimization process. The Partnership nevertheless listed in its response several continuing Mg projects within the 67 percent of DOE’s FY 2012 budget that is devoted to metals development. Phase 3 Recommendation 3-24 urged the development of methods to recy- cle carbon-fiber composites. The Partnership is devoting 18 percent of its FY 2012 Lightweight Materials budget to carbon-fiber projects, including recycling. Although this is responsive to the committee recommendation, it can be argued that carbon fiber offers perhaps the greatest opportunity for weight reduction while maintaining structural integrity, and hence the huge challenge of doing so at low cost could deserve a greater share of the materials budget. While increased emphasis on low-cost carbon fiber would be desirable, the committee continues to believe that much of the MTT work on light metals and materials substitution demonstrations is not precompetitive and would be best performed by the private sector. Funding currently allocated to these activities
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110 REVIEW OF THE RESEARCH PROGRAM OF THE U.S. DRIVE PARTNERSHIP could well be used more effectively by other technical teams or on materials research needs identified by those other teams. Recommendation 3-17. The Partnership should expand its current work on low-cost carbon-fiber precursors, manufacturing, and recycling. This work could also potentially help to reduce the cost of high-pressure hydrogen storage tanks. Recommendation 3-18. The materials technical team should expand its outreach to the other technical teams to determine the highest-priority collective Partner- ship needs, and the team should then reassess its research portfolio accordingly. Any necessary reallocation of resources could be enabled by delegating some of the highly competitive metals development work to the private sector. REFERENCES Bandivadekar, A., K. Bodek, L. Cheah, C. Evans, T. Groode, J. Heywood, E. Kasseris, M. Kromer, and M. Weiss. 2008. On the Road in 2035: Reducing Transportation’s Petroleum Consumption and GHG Emissions. MIT Laboratory for Energy and the Environment, Cambridge, Mass. Report No. LFEE 2008-05 RP, July. Available at http://web.mit.edu/sloan-auto-lab/research/ beforeh2/otr2035/On%20the%20Road%20in%202035_MIT_July%202008.pdf. Debe, M.K. 2011. “Advanced Cathode Catalysts and Supports for PEM Fuel Cells.” Presentation at the DOE 2011 Annual Merit Review, May 9-13, Washington, D.C. Available at http://www. hydrogen.energy.gov/annual_review11_fuelcells.html. Debe, M.K. 2012. “Advanced Cathode Catalysts and Supports for PEM Fuel Cells.” Presentation at the DOE 2012 Annual Merit Review, May 14-18, Arlington, Va. Available at http://www. hydrogen.energy.gov/pdfs/review12/fc001_debe_2012_o.pdf. DOE (U.S. Department of Energy). 2010a. FY 2010 Progress Report for the Hydrogen and Fuel Cells Program. Available at http://www.hydrogen.energy.gov/annual_progress.html. DOE. 2010b. Multi-Year Program Plan 2011-2015. December. Washington, D.C.: Office of Vehicle Technologies, Energy Efficiency and Renewable Energy. DOE. 2011. FY 2011 Progress Report for the Hydrogen and Fuel Cells Program. Available at http:// www.hydrogen.energy.gov/annual_progress.html. DOE. 2012a. Department of Energy FY 2013 Congressional Budget Request. Vol. 3. DOE/CF-0073. February. Washington, D.C.: DOE Office of the Chief Financial Officer. DOE. 2012b. FY 2011 Annual Progress Report for Energy Storage R&D, Hybrid Electric Systems Team. January. Washington, D.C.: Office of Vehicle Technologies, Energy Efficiency and Re- newable Energy. FCFP (FreedomCAR and Fuel Partnership). 2011. 2010 Highlights of Technical Accomplishments. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/2010_fcfp_accomplishments_rpt. pdf. Gaines, L. 2011. Recycling of Li-ion Batteries. Illinois Sustainability Technology Center, P rairie Research Institute. November 15. Available at http://www.istc.illinois.edu/about/ SustainabilitySeminar20111115.cfm. Hawkins, S., F. Billotto, D. Cottrell, A. Houtman, et al. 2012. Development of General Motors’ eAssist Powertrain. SAE Int. J. Alt. Power. 1(1):308-323. doi:10.4271/2012-01-1039.
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VEHICLE SUBSYSTEMS 111 Howell, D. 2012. “Overview of Battery R&D Activities.” Office of Vehicle Technologies Program, Energy Efficiency and Renewable Energy. Presentation at the DOE 2012 Annual Merit Review, May, Arlington, Va. Available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_re- view_2012/energy_storage/es000_howell_2012_o.pdf. Myers, D., X. Wang, N. Kariuki, R. Subbaraman, R. Ahluwalia, and X. Wang 2011. “Polymer Elec- trolyte Fuel Cell Lifetime Limitations: The Role of Electrocatalyst Degradation.” Presentation at the DOE 2011 Annual Merit Review, May 9-13, Washington, D.C. Available at http://www. hydrogen.energy.gov/pdfs/review11/fc012_myers_2011_o.pdf. Myers, D., X. Wang, N. Kariuki, S. DeCrane, T. Nowicki, R. Subbaraman, S. Arisetty, and R. Ahlu- walia. 2012. “Polymer Electrolyte Fuel Cell Lifetime Limitations: The Role of Electrocatalyst Degradation.” Presentation at the DOE 2012 Annual Merit Review, May 14-18, Arlington, Va. Available at http://www.hydrogen.energy.gov/pdfs/review12/fc012_myers_2012_o.pdf. NRC (National Research Council). 2008. Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report. Washington, D.C.: The National Academies Press. NRC. 2010. Review of the Research Program of the FreedomCAR and Fuel Partnership: Third Re- port. Washington, D.C.: The National Academies Press. Olszewski, M. 2011. Oak Ridge National Laboratory Annual Progress Report for the Power Electron- ics and Electric Machinery Program. October. ORNL TM-2011/263. Available at http://info. ornl.gov/sites/publications/files/Pub31483.pdf. Snyder, K. 2012. “Overview and Progress of United States Advanced Battery Consortium (USABC) Activity.” Presentation at the DOE 2012 Annual Merit Review, May, Arlington, Va. Avail- able at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2012/energy_storage/ es097_snyder_2012_o.pdf. Stetson, N.T. 2010. “Hydrogen Storage.” Presentation at the DOE Annual Merit Review, June 8, Washington, D.C. Available at http://www.hydrogen.energy.gov/pdfs/review10/st00a_ stetson_2010_o_web.pdf. Stetson, N.T. 2011. “Hydrogen Storage—Session Introduction.” Presentation at the DOE Annual Merit Review, May 9, Washington, D.C. Available at http://www.hydrogen.energy.gov/pdfs/ review11/st000_stetson_2011_o.pdf. Stetson, N.T. 2012. “Hydrogen Storage Overview.” Presentation at the DOE Annual Merit Review, May 15, Arlington, Va. Available at http://www.hydrogen.energy.gov/pdfs/review12/St000_ Stetson_2012_o.pdf. Sunita, S. 2011. “Overview of Hydrogen and Fuel Cell Budget.” DOE Fuel Cell Technologies Pro- gram, Stakeholders Webinar—Budget Briefing, February 24. Available at http://www1.eere. energy.gov/hydrogenandfuelcells/pdfs/budget_webinar_fy12.pdf. U.S. DRIVE. 2011. Highlights of Technical Accomplishments. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Available at http://www1.eere.energy.gov/vehicle- sandfuels/pdfs/program/2011_usdrive_accomplishments_rpt.pdf. Wagner, F.T., B. Lakshmanian, and M.F. Mathias. 2010. Electrochemistry and the future of the auto- mobile. Journal of Physical Chemical Letters 1:22014. Weiss, M.A., J.B. Heywood, E.M. Drake, A. Schafer, and F.F. AuYeung. 2000. On the Road in 2020: A Life-Cycle Analysis of New Automobile Technologies. MIT Energy Laboratory Report No. MIT EL 00-003, Cambridge, Mass. Available at http://web.mit.edu/energylab/www/pubs/ el00-003.pdf. Wipke, K., S. Sprik, J. Kurtz, T. Ramsden, C. Ainscough, and G. Saur. 2012. National Fuel Cell Elec- tric Vehicle Learning Demonstration Final Report. Technical Report NREL/TP-5600-54860. July. Contract No. DE-AC36-08GO28308. Golden, Colo. Zoepf, S.M. 2011. Automotive Features: Mass Impact and Deployment Characterization. Thesis, Massachusetts Institute of Technology, Master of Science in Technology and Policy. Available at http://web.mit.edu/sloan-auto-lab/research/beforeh2/files/Zoepf_MS_Thesis.pdf.