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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report 3 Vehicle Subsystems INTRODUCTION The long-range goals of the FreedomCAR and Fuel Partnership—to transition to a transportation system “that uses sustainable energy resources and produces minimal criteria or net carbon emissions on a life cycle or well-to-wheels basis”—are extremely ambitious (DOE, 2004a). The difficulties are compounded when the additional constraints associated with the FreedomCAR and Fuel Partnership are imposed: energy freedom, environmental freedom, and vehicle freedom. These goals and associated constraints effectively eliminate the continued evolution of the gasoline-fueled internal combustion engine (ICE) vehicle as a possible answer. “Sustainable energy resources” and “energy freedom” both suggest non-petroleum-based alternative fuels. The emphasis on “net carbon emissions” and “environmental freedom” suggests that CO2 and other emissions from the production and consumption of alternative fuels should be reduced, through highly efficient processes, to minimize adverse environmental effects. Finally, “vehicle freedom” implies that the fuel and onboard energy conversion systems should not limit the options and choice that buyers expect to have available in their personal vehicles. These goals, if attained, are likely to mean new transportation fuel(s) utilized in more efficient power plants in lighter vehicles having reduced power requirements while maintaining equivalent utility and safety. DOE envisions that the path to achieving the long-term goals of the FreedomCAR and Fuel Partnership involves a transition from improved gasoline- and diesel-fueled ICE vehicles, to a greater utilization of gasoline- and diesel-fueled hybrid electric vehicles (HEVs), to hydrogen-fueled ICEs and HEVs, and ultimately to hydrogen-fueled fuel cell vehicles (DOE, 2004a). For
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report this transition to take place, the industry will require enhanced understanding in many areas so that it can develop new vehicle subsystems and vastly improved vehicles. The DOE-sponsored activities described in this section are intended to provide such understanding. Near-term reductions in fuel consumption and emissions can be accomplished by improving ICEs. Specifically, better understanding of the combustion process and how emissions are produced could both increase efficiency and decrease engine-out emissions. Higher thermal efficiency means reduced fuel consumption and lower engine-out emissions means less extensive, and probably less expensive, exhaust aftertreatment systems. Improved ICEs, which could come in the near term, would benefit both conventional vehicles and HEVs. The fuel cell subsystem is an energy converter that has the potential to be more efficient than an ICE. However, fuel cell systems of the type deemed appropriate for transportation systems use only hydrogen as fuel. The hydrogen can be stored onboard the vehicle in pure form or it can be extracted from hydrogen-bearing hydrocarbon fuels and water using onboard fuel processors. However, DOE effectively eliminated the latter alternative from its R&D portfolio after years of R&D offered little prospect of meeting essential cost and performance targets within the program time frames. Without this option, sufficient pure hydrogen must be carried onboard the vehicle to meet range requirements. Further, since it is extremely difficult with typical light-duty vehicles to carry hydrogen quantities with an energy content equivalent to that of a typical fuel tank filled with gasoline, it is imperative to minimize fuel consumption. This implies reducing the mass of the vehicle and maximizing the efficiency of the energy converter. Current experimental hydrogen-fueled fuel cell systems demonstrate efficiencies approaching 50 percent over a fairly wide range of operation. Further, such systems produce zero criteria emissions (occasional discharges of small quantities of hydrogen may occur). However, there are performance, durability, and cost issues to be resolved if fuel cells are to become viable options for personal transportation vehicles. Hybrid electric vehicles require compact, efficient, and low-cost power electronics and energy storage systems as well as other advanced electrical components to make vehicle costs and weights competitive with conventional vehicles. Many of the same technologies also are applicable to fuel cell vehicles since fuel cell vehicles will be basically electric vehicles with various degrees of hybridization. Consequently, advances in the power electronics and electrical subsystems are critical for improved viability of both mid-term HEVs as well as longer-term fuel cell vehicles. One important means of minimizing fuel consumption for mid-term HEVs and longer-range fuel cell vehicles is the partial recovery of vehicle kinetic energy during deceleration and stopping. Thus, these vehicles will need some form
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report of energy storage capable of accepting some of this energy (regenerative braking) and providing it back to the drive train for propulsive power. The mostly likely form of such energy storage is electrochemical (batteries), but ultracapacitors are also being investigated. For such relatively small-scale energy storage, the most important parameters are cost per kilowatt, specific power (kW/kg), and cycle and calendar life. Even though hybrid electric vehicles are currently on the market, the projected cost savings due to higher fuel mileage will probably not offset the higher initial cost of the vehicle at foreseeable fuel prices. This implies that further cost reductions may be necessary for the hybrid vehicles to gain widespread acceptance and have a significant impact on fleet fuel mileage. Such cost reductions require additional understanding in the areas discussed. Beyond the need for small-scale energy storage required to handle energy from regenerative braking is the need for sufficient on-board energy storage to propel the vehicle for a reasonable range without use of the power plant (e.g., fuel cell or engine). Moving in this direction could add design flexibility to HEVs and reduce some of the performance requirements for the fuel cells (e.g., start-up time and power ramp-up rate) in a fuel cell vehicle. Further increases in on-board energy storage capacity could enable plug-in hybrid vehicles (a vehicle whose battery could be recharged by plugging into a source of electricity while it is parked) or even all-electric vehicles. Both plug-in hybrids and all-electric vehicles could provide the immediate benefit of shifting some transportation energy demand from onboard petroleum-based fuels to the electric grid, which is mostly non-petroleum-based but, of course, not emission-free. The most important parameters for these energy storage systems will be cost per kilowatt-hour, specific energy (kWh/kg), cycle life, and calendar life. These storage systems would also have to maintain adequate specific power (kW/kg), even at low states of charge and low ambient temperatures. Irrespective of the propulsion technology, reducing the mass of a vehicle for a given mission will have the effect of reducing fuel consumption. However, to conform to FreedomCAR goals, any such mass reduction would have to be accomplished without compromising safety or overall vehicle utility. To accomplish significant weight reductions, several materials, including aluminum, high-strength steel (HSS), and carbon-fiber-reinforced polymer composites could replace a large part of the (mostly) mild steel currently used. Other material substitutions, such as cast magnesium, in other vehicle components could further decrease vehicle weight. Unfortunately, thus far all of these potential material substitutions would result in large cost penalties. Therefore, research in materials production and manufacturing techniques is essential if the mass-reduction benefits of these materials are to be realized. The following sections discuss in more detail the issues associated with the alternative technologies for vehicle components.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report ADVANCED COMBUSTION ENGINES, EMISSION CONTROLS, AND HYDROCARBON FUELS Introduction The ICE plays a critical transitional role in achieving the FreedomCAR and Fuel Partnership’s long-term goal. If the Partnership meets its objective—namely, of enabling the private sector to make a commercialization decision on fuel cell vehicles by 2015—it would still be decades after that before these vehicles penetrate the market sufficiently to have a measurable impact on total fleet fuel consumption. If commercialization is delayed beyond 2015, the impact will be pushed even further into the future. In contrast, improvements in engine and aftertreatment technologies could be incorporated into a large spectrum of new vehicles quite rapidly. With approximately 16 million new vehicles sold in the United States every year, improving the energy efficiency of vehicles sold now will have near-term and growing impact on the petroleum consumption of the entire vehicle fleet. FreedomCAR’s transition strategy to hydrogen-fueled vehicles envisions a sequence of improved ICEs, increasing use of advanced ICE hybrid vehicles and hydrogen-fueled ICE hybrid vehicles, and—ultimately—a transition to hydrogen-fueled fuel cell vehicles (DOE, 2004a). The focus of the advanced combustion engines and emission controls (ACEC) activity of the FreedomCAR and Fuel Partnership is to improve the efficiency of the engines of these transitional vehicles and reduce their emissions. To this end ACEC has established a sequence of technical targets during the transition (Table 3-1). The benefits of improved ICEs could begin in the very near term. However, the total impact would be limited by the slow rate of market penetration and the large number—roughly 225 million—of light-duty vehicles in the current fleet. As part of the Government Performance and Results Act, EERE estimated the potential fleet fuel savings from introducing these new technologies to the market. In performing this analysis, it was assumed that the technical targets of Table 3-1 were met, and because these new technologies would add to the cost of the vehicle, the analysis was performed on a cost-competitive basis, assuming that the incremental cost of the technology is paid back by fuel savings in 3 years. Vehicle price and fuel economy were the two most important attributes characterized (DOE, 2004b). The results of the analysis indicated that for light-duty vehicles, oil savings, in millions of barrels per day (mbpd), from diesels and diesel hybrid vehicles would be approximately 0.05 mbpd in 2015, 0.22 mbpd in 2020, and 0.57 mbpd in 2025. These are small reductions considering the light-duty vehicle petroleum consumption in 2004 was approximately 8 mbpd. However, a different rate of market penetration would change these projections. These new technologies would be incorporated into the market more quickly, as enabling technologies, if the market drivers were
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report TABLE 3-1 Goals and Status of the Advanced Combustion Engines and Emission Controls Activity Goals Unit 2004 Status Goals by Fiscal Year PFI DI FY07 FY10 FY13 FY15 For hydrocarbon fuel ICE peak brake thermal efficiency % 30 41 43 45 46 ICE powertrain costa $/kW 20 30 35 30 30 Projected vehicle emissions Tier 2 <Bin 10 Bin 10 Bin 5 Bin 5 Bin 5 Emission control fuel economy penaltyb % <5 <4 <3 Emissions durability 1,000 miles 120 120 120 120 120 120 For hydrogen fuel H2 ICE peak brake thermal efficiency % 38 45 45 H2 ICE powertrain costa $/kW 45 30 Projected vehicle emissions Tier 2 <Bin 5 Bin 5 Bin 5 NOTE: PFI, port fuel injection; DI, direct injection. The emission standards are based on EPA Tier 2 emission regulations. The description of the test procedures and the regulated levels for each Bin may be found at <http://www.dieselnet.com/standards/us/light.html>. aHigh-volume production of 500,000 per year. bFuel economy penalty over combined federal test procedures due to emission control relative to diesel vehicle with 2003 emissions. SOURCE: K. Howden and R. Peterson, “Advanced combustion and emission controls (ACEC) activities,” Presentation to the committee on November 17, 2004. to change—for example, if the price of fuel were to increase or by any of the policy alternatives discussed in Chapter 2. Program Technologies Because a primary goal of the program is to reduce fuel consumption, the most fuel-efficient power plant available is being considered as the basis for the research effort. For light-duty vehicle applications, the compression ignition direct injection (CIDI, diesel) engine is the most fuel-efficient engine currently in production. It is well known, however, that current diesel engines will not meet future emission standards. Therefore, to reduce fuel consumption through the more widespread introduction of diesel engines into the market, advances must be made in emission reduction technologies. Here, the most significant barriers are cost and insufficient fundamental understanding of engine combustion phe-
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report FIGURE 3-1 Technical areas and relative funding for the ACEC activity, FY04. DPF, diesel particulate filter; HCCI, homogeneous charge compression ignition; LTC, low-temperature combustion; PM, particulate matter; SCR, selective catalytic reduction. SOURCE: Response to questions from the committee to DOE, received January 19, 2005. nomena, exhaust emission control technologies, and engine controls. It is important to realize that the phenomenon of diesel combustion and its emission reduction is fundamentally different from that of the conventional spark ignition engine. The technologies are not transferable. New technologies are required. The research directly addresses all of the barriers except cost. The operating paradigm of the program is to expand the fundamental understanding of combustion, aftertreatment, and controls phenomena in a precompetitive research environment and then let industry address cost as it works to incorporate the new technologies into vehicle power plants. The individual project topic areas within each research focus are shown in Figure 3-1. Details on the specific research projects within those topics are available in the DOE annual report (DOE, 2003). The vehicle manufacturers all have in-house programs that could be grouped under the topic headings given in Figure 3-1. Government-supported research efforts in these areas differ from industry efforts in the nature of the understanding being sought. Industry is focused on trying to find workable engineering embodiments of the various technologies—for example, establishing the operating parameters of an engine that facilitate low-temperature combustion (LTC); a classification of combustion processes that includes homogeneous charge compression ignition (HCCI) combustion;
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report and devising strategies to switch from low-temperature combustion to conventional diesel combustion when loads outside the LTC regime are required. The activities supported by federal money at the national laboratories and universities are pursuing a fundamental understanding of the processes that will enable LTC technology to be extended or optimized. For example, federal programs are working to understand the thermochemical interactions that constrain LTC to its current regime. If these are better understood, a wider range of LTC will be possible, with a corresponding improvement in efficiency and reduction in emissions. As seen from the budget distribution (Figure 3-1), the research effort tilts strongly toward the fundamentals of combustion and aftertreatment, with smaller efforts addressing component subsystems and sensors. The subsystem and sensor research programs are aimed at the question of controls. Control algorithms for the power train system will need inputs from sensors that are monitoring component performance; commands would then be issued, adjusting the engine and aftertreatment system operation. During this last year the ACEC technical team has shifted the emphasis of its research programs. If the current diesel engine combustion process were left unaltered, the conversion efficiency for the nitrogen oxides (NOx) and particulate matter (PM) aftertreatment systems would need to be maintained at levels in excess of 90 percent for the lifetime of the vehicle—a huge challenge. The emphasis has therefore shifted from controlling emissions with aftertreatment technologies to reducing the in-cylinder formation of emissions, thereby reducing the burden on exhaust gas aftertreatment. Research has demonstrated that LTC, of which HCCI combustion can be viewed as a subset, has the potential to generate very low levels of NOx and PM (Akihama et al., 2001; Siebers and Pickett, 2004). The challenge is that to date, LTC has been limited to low-load operation, and the parameter space for controlling it is not well understood. The research effort on NOx and particulate matter aftertreatment is very closely aligned with the effort of industrial partners. The formulation and development of new or improved catalysts is conducted primarily in industry, where catalyst suppliers team with vehicle or engine manufacturers. Catalyst mechanisms such as sulfur poisoning, desulfation of lean NOx traps, thermal aging, and soot filter regeneration are being investigated at the national laboratories using diagnostic microscopy and spectroscopy techniques not readily found in industry. These investigations use both model catalysts and real formulations. The data are being made available for the development of computer simulations of emission control devices, being done at the national laboratories and universities involved in the Crosscut Lean Exhaust Emission Reduction Simulation (CLEERS) activity. The direct fueling of ICEs with hydrogen is also under investigation. This is an area where partner companies have in-house programs, so the DOE-supported effort is minimal. Using hydrogen in an ICE would of course provide some of the emission benefits at much lower capital cost than changing to fuel cells and
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report electric propulsion. The focus of DOE-funded research in this area is direct injection (DI) hydrogen engines. DI hydrogen engines offer higher power density than engines in which the hydrogen is introduced in the intake manifold. Fueling of ICEs with hydrogen through an intake manifold is also under investigation. Using hydrogen as an ICE fuel is not new. Because hydrogen has such wide flammability limits and high flame speeds, it may be possible to extend the lean operating limits of the engine, which would reduce fuel consumption and emissions. The issues associated with implementing this are pragmatic and not fundamental. Consequently much of the research on direct fueling on ICEs with hydrogen is being done by industry, with little or no DOE involvement. One challenge with direct fueling an engine with hydrogen is the loss of volumetric efficiency because the fuel is gaseous. In addition, lean burn mixtures—combined with loss of volumetric efficiency—causes a large power reduction (for the same displacement engine), necessitating a supercharger or turbocharger to bring power levels back up. If a stoichiometric mixture of hydrogen and air is introduced into the engine in the intake manifold, hydrogen will comprise approximately 30 percent of the mixture by volume. This disadvantage can be overcome if hydrogen is directly injected into the cylinder. In this connection some fundamental issues need investigation. The penetration and mixing phenomenon surrounding low-density, high-velocity gas inside a cylinder during direct injection is the subject of DOE-supported investigations at the Sandia Combustion Research Facility. These activities are aimed at increasing the power density of a hydrogen-fueled engine. Budget and Organization The FreedomCAR and Fuel Partnership is focused on light-duty passenger vehicles. However, the fundamental knowledge being pursued to enable fuel-efficient technologies is not exclusive to light-duty passenger vehicles. It also applies to engines used in the commercial sector—for example, heavy-duty trucks. To capitalize on these synergies in the combustion engines and emissions technical area, the FreedomCAR and Fuel Partnership is collaborating with the 21st Century Truck Partnership, a partnership of DOE, DOD, EPA, and DOT and 15 industrial partners. The combined budget for advanced combustion for both the FreedomCAR and Fuel Partnership and the 21st Century Truck Partnership for FY04 was $54.4 million. Of this total, $19.5 million was under the direct control of the FreedomCAR and Fuel Partnership. The distribution of these directly controlled funds to the research topics is shown in Figure 3-1. The vision of the Partnership is that hybrid vehicles will be an important part of the transition. However, because hybrid vehicles are already on the market and are being further developed by the individual automotive companies that are part of the partnership, government-funded efforts for the ACEC activity aim to get a better fundamental understanding of ICEs and aftertreatment systems. This should
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report lead to better engines, which would become part of better hybrid power trains. The technical goals in Table 3-1 are related to engine and aftertreatment performance; hybrid vehicles as such do not appear. The technical teams, made up of researchers at government laboratories, including the DOE national laboratories, and industry and university laboratories, have established a good process for interaction, feedback, and review. There is interaction between the technical teams of FreedomCAR and 21st Century Truck in the form of crosscut teams, workshops, biannual program reviews, and discussions facilitated by memoranda of understanding. The industrial partners provide input for the setting of research priorities through the workshops and technical reviews, whose outcomes are reflected in DOE solicitations for proposals. As technologies are considered for commercialization the developmental research is performed by vertically integrated teams of industry partners. Achievements Quantifying the achievements of the ACEC activity is challenging in that the primary outcome of the government-supported research is new knowledge. In this sense, progress is good. The advanced combustion and emissions control technical team has demonstrated new understanding of the LTC process, including HCCI, and has achieved low-temperature operation in running engines. New understanding of phenomena occurring at the spray nozzle tip, where fuel atomization and air entrainment begin, has been obtained through x-ray imaging, and the boundaries of clean, injection-driven combustion are being expanded. Operational windows of lean catalyst and mechanisms of catalyst poisoning are being studied, and a real-time exhaust stream particulate sensor is being tested. These are important accomplishments; however, it is not known at this time to what extent these advancements in knowledge will be integrated into light-duty vehicle power plants in the near term. Comments and Recommendations The various types of ICEs will play a critical transitional role in achieving the FreedomCAR and Fuel Partnership’s long-term goal. Even assuming the eventual success of hydrogen as a primary transportation fuel, for several decades ICE will be the automotive power plant that consumes most of the fuel in the fleet. Reducing its fuel consumption and emissions is therefore critically important. Novel emission technologies are needed, and the cooperation of energy companies in such research will increase the likelihood of finding solutions. The energy companies joined the Partnership in September 2003, adding a new dimension to the program: Now, the impact of fuel modification or substitution on the combustion, emission, and aftertreatment performance can be examined. The variety of fuels that could be investigated is huge, as is the number of
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report pragmatic constraints relative to refining and distribution that need to be considered. The role of fuel characteristics in ongoing research and how best they should be integrated into the program is not well known at this time. Many of the research activities within the ACEC use pure fuels or controlled mixtures. Fuel composition could be systematically varied to enhance our understanding of different chemical processes during combustion and the reduction of emissions by catalyts or to evaluate the impact of fuel composition on the fundamental processes being studied. The issue of real-world fuels found in the marketplace and whether their properties can be used as enablers to achieve desirable results is not part of the program at this time. It is difficult to know whether this will be a fruitful area of research, but it should be considered. It seems that the energy company partners are still not completely integrated into this research program. Much of the fundamental work is being done with pure fuels or simple blends. Knowing the extent to which these pure fuels or simple blends will be representative of real-world fuels expected to be available in the marketplace (for example, low-sulfur fuels or reformulated gasoline contain small amounts of sulfur or oxygenates) or knowing their deficiencies relative to real-world fuels will be important in interpreting the fundamental results achieved in the laboratory for expected behavior in real-world application. Recommendation. DOE should encourage the energy industry to become involved in establishing research parameters for the work on pure fuels that will be most relevant to real-world fuels expected in the marketplace. If specific fuel blends are identified as having a positive impact on meeting the technical targets for an advanced ICE, it will be important to understand the ability of the energy companies to make those blends and what the costs and capital requirements would be. Recommendation. DOE and the energy industry should develop refinery models for making tailored fuel blends. At present, there is still no commercially attractive aftertreatment system for CIDI engines that meets the EPA Tier 2, Bin 5, emission standard. Industry is intensely pursuing the development of various technologies for PM and NOx removal. In general, aftertreatment systems are unsatisfactory in terms of their cost, fuel penalty, durability, or effect on engine performance. This is particularly so for NOx removal devices. Engine manufacturers and catalyst companies devote significant in-house effort to satisfying the Tier 2 standard. In accordance with the mission of the FreedomCar and Fuel Partnership to “examine precompetitive, high-risk research,” the ACEC technical team is encouraged to identify breakthrough and innovative technologies that could provide long-term solutions to the CIDI emissions problems and to begin to anticipate, analyze, and
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report look for solutions to potential emissions problems and solutions for emerging fuels, the fuel infrastructure, and propulsion systems. For example, the emissions problem associated with a distributed hydrogen production system could be quite different and costly, and treatment of emissions from low-temperature combustion could pose new challenges. Recommendation. Increased emphasis should be placed on novel emission control technologies, and the advanced combustion and emission controls technical team should plan for, analyze, and seek solutions for emission problems associated with emerging fuels, fuel infrastructure, and propulsion systems. FUEL CELLS If hydrogen is to account for a significant share of the fuels used for transportation, the transition will be greatly facilitated by fuel cell power systems whose performance and cost are compatible with automotive requirements. This is especially true if costs and onboard storage continue to be problem areas for hydrogen. Fuel cells promise higher conversion efficiencies for hydrogen than ICEs, thus reducing fuel consumption and onboard storage requirements by increasing equivalent fuel economy. Fuel cell systems are operating successfully on hydrogen in dozens of experimental vehicles in the United States and several other countries. These systems are not compatible, however, with the requirements for mass-manufactured automobiles. They are too expensive, too large, and too heavy, and they have performance problems such as slow start-up and slow power transients, and poor durability, such as degraded performance and limited component life. The status in 2004 of these and other characteristics as well as the targets for 2005 and 2015 are shown in Table 3-2. As can be noted, the 2005 targets (established in 2003) were essentially being met in 2004 in some areas but still had a long way to go in others, such as durability, survivability, and start-up time. Indeed, a review of these parameters not only through the early stages of the FreedomCAR program but also through the entire PNGV program preceding FreedomCAR would show impressive and continuing progress in every area. However, comparing the 2005 targets with the 2015 targets shows clearly that much additional progress is needed. As delineated in Table 3-3, the fuel cell program is focused on R&D to improve fuel cell technologies for both transportation and stationary applications. The fuel cell program is being implemented by DOE’s Office of Hydrogen, Fuel Cells, and Infrastructure Technology Program (HFCIT), which is identifying and developing the critical technology and knowledge needed. The fuel cell part of the FreedomCAR and Fuel Partnership is organized to facilitate the engagement of automobile developers, component suppliers, and related participants so as to meet the 2015 objectives. It is a multidimensional, complex effort spanning many
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report Energy efficiency on load profile % 90 90 90 90 90 90 Cycle life profiles (engine starts) cycle 450,000 300,000 300,000 TBD 1,000 at 80% DOD Calendar life year 15 15 15 15 15 15 10 10 Cold cranking power at −30°C kW 8 at 21V minimum for 2 s 5 for 2 s 7 for 2 s 5 for TBD min Maximum system weight kg 10 25 35 40 60 32 Maximum system volume liter 9 20 28 32 45 26 Price at 100,000 units/year $ 150 260 360 500 800 400 Price for 25,000 units (40 kWh) $/kWh <150 100 Maximum operating voltage Vdc 48 48 48 400 400 440 Minimum operating voltage Vdc 27 27 27 >0.55 x Vmax Maximum self-discharge Wh/d <20 <20 <20 50 50 50 Operating temperature range °C −30 to +52 −30 to +52 −40 to +50 −40 to +85 Survival temperature range °C −46 to +66 −46 to +66 NOTE: M-HEV, mild hybrid electric vehicle; P-HEV, power assist hybrid electric vehicle; DOD, depth of discharge. SOURCE: T. Duong and A. Habb, “Electrochemical energy storage,” Presentation to the committee on November 17, 2004.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report applied and long-term research groups are crucial to meeting all the target goals of a high-power battery. At present less than 25 percent of the total energy storage budget is allocated to the applied and long-term research. This share should be increased significantly. Most of the work sponsored by the energy storage technology team is directed to the development of high-power batteries. Specifically, in FY04, 80 percent of the funds were spent on high-power batteries for HEVs. Some funds were used to develop high-energy batteries to meet the target for an EV. The applied and long-term exploratory research on new materials and electrochemical couples is also primarily for high-energy batteries. The committee recognizes that the distinction between a high-power and high-energy battery is somewhat arbitrary, particularly when attempting to gain a basic understanding of the factors limiting the performance of the battery. The fundamental property of a battery is its specific energy, and generally the specific power is determined by design optimization for a given application. Thus, the Li-ion battery is a high-energy battery that has been optimized to meet the power and cycle life requirements of a high-power battery for HEV applications, and increased effort on high-energy batteries will increase the likelihood of meeting the high-power battery goals for hybrid application. The target requirements for the HEV listed in Table 3-5 show that as one moves from a 42-V application to a more demanding power-assist HEV and then to a FCHEV, the power requirement increases from 13 kW to 25 kW. Not only is the power increased for the more demanding hybrid applications, but it is also required for a longer time, increasing from 2 s in the 42-V application to 18 s for a FCHEV (DOE, 2004a). Thus one would require a battery with not only a higher power rating but also significantly higher specific energy. It is clear that various hybrid designs will have different power requirements and there is continuum of energy requirements. Higher energy can be utilized to gain a better mix of power and energy density in battery design for a given application or it can also be used to optimize the size of the ICE engine. The target requirements for an EV are listed in Table 3-5. The main requirement is a high-energy battery with specific energy of 200 Wh/kg and 2:1 power to energy ratio. An EV represents an alternative route to achieving the primary goal of the FreedomCar and Fuel Partnership: energy independence and an environmentally friendly transportation system. The development of high-energy batteries is consistent with DOE’s goal of investing in high-risk technologies. The challenge of such an effort is probably no greater than the challenges of hydrogen storage and the hydrogen infrastructure requirements for a hydrogen fuel cell vehicle. The committee feels that the effort for high-energy batteries should be significantly increased. Ultracapacitors The double-layer capacitor (DLC), commonly referred to as an ultracapacitor, is an energy storage device having a state-of-the-art energy density about 1/10
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report that of a Li-ion battery but a power density about 10 times that of a Li-ion battery. DLCs in large sizes (>5,000 farads) are receiving considerable international research attention and could prove to be an important element in a FCHEV. Current research is focused on innovative electrode structures and new electrolytes, the goal being to achieve both a higher cell voltage and a larger specific capacitance. The DLC has no mass transport and compared with a battery, has a considerably longer cycle life and better tolerance of temperature extremes. As noted in the section “Electric Propulsion, Electrical Systems, and Power Electronics,” the FreedomCAR program has benchmarked commercially available DLCs. In view of the potential benefits of a high-energy-density DLC, the funding of research in advanced DLC technologies may be warranted. Comments and Recommendations Efforts directed toward the development of new materials and electrochemical couples in these programs present the best chance to remove the major barriers of abuse tolerance, cost, and calendar life for high-power batteries. Recommendation. DOE should direct more of its effort and funding for high-power batteries for HEVs to applied and long-term exploratory research rather than battery development. High-energy batteries for electric vehicles and plug-in hybrid applications would also serve to meet the FreedomCar and Fuel Partnership goals. Further, more support for high-energy battery research would increase the likelihood of meeting the requirements of various HEVs for high-power batteries. Recommendation. A significantly larger effort and higher priority should be placed on searching for breakthrough technology in the area of high-energy batteries for electric vehicles. Recommendation. In view of the potential benefits of a high-energy-density DLC in hybrid vehicles, the energy storage technical team, in conjunction with the electrical and electronics system technical team, should maintain an activity that explicitly monitors progress of international DLC research programs and should consider funding research in advanced DLC technologies. ELECTRIC PROPULSION, ELECTRICAL SYSTEMS, AND POWER ELECTRONICS The multiple systems in both hybrid electric vehicles (HEVs) and fuel cell hybrid electric vehicles (FCHEVs) require both control and coordination. These functions will be provided by electronics, both power- and signal-level. Although
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report a fuel cell (FC) alone may be compatible with the dynamic requirements of electrical traction, regenerative braking requires that the FC be augmented by an energy storage device—e.g., a battery or an ultracapacitor. This electrical energy storage may also be used to enhance the dynamic performance of the propulsion system by, for instance, providing fast transient power for acceleration. The battery may also be used for drive-away when fuel cell start-up time is excessive. The charge/discharge cycles of this device will require power electronics. Control of the FC itself will also require electrical system controls. The integrating role of the vehicle electrical system makes it an important technology, both functionally and economically. However, the FreedomCAR goal for the electrical and electronics (EE) technical team, as stated, is limited to the propulsion system—that is, the electric machine and the power electronics to drive it.3 Although the multiyear plan of the FCVT program also states this goal, the surrounding discussion does refer to many of the other EE functions necessary for the complete system (DOE, 2004a; FCVT, 2004). Program Status and Progress Within the restricted goals established for the EE systems, the EE technical team has built on the results of the motor and electronics development in the PNGV program. The power electronics technology for FreedomCAR is evolving from the PNGV-funded automotive integrated power module (AIPM) developments. While several companies (one is Rockwell Automation) continue to develop AIPMs that may be applicable to FreedomCAR, the FCVT program is currently funding work at Semikron. Table 3-6 shows the power electronics and traction motor status in 2003, the 2010 targets, and the gap between status and target. The reported status of the power electronics in November 2004 had not changed from that in 2003. The principal challenges are thermal performance, lifetime, and cost. Although the 2003 status for power electronics shows a lifetime of 15 years, this is with a coolant temperature of 70°C. The lifetime would be considerably less at the 2010 target temperature of 105°C. Although the specific power and volumetric power density of the motor are still shy of their 2010 targets, it is the motor cost and thermal performance that remain the most significant challenges. The committee is not convinced that the motor cost goal of $7/kW is achievable, since the cost is principally a matter of commodity prices (e.g., copper and iron prices), and it seems unlikely that cost can be reduced much through research. Thermal performance of the power electronics has been a challenge using conventional component technology, and the EE technical team is exploring 3 S. Rogers and V. Garg, “Electrical and electronic tech team—NAS review,” Presentation to the committee on November 18, 2004.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report TABLE 3-6 Technical Targets for Power Electronics and Electric Motors 2003 Status 2010 Gap Power electronics (inverter/controller)a Specific power at peak load (kW/kg) 11 >12 1 Volumetric power density (kW/L) 11.5 >12 0.5 Costa ($/kW peak) 6 <5 1 Efficiency (%) 97 97 0 Coolant inlet temperature (°C) 70 105 35 Lifetime (yr) 15 15 0 Electric motors (traction)a, b Specific power at peak load (kW/kg) 1.0 >1.3 0.3 Volumetric power density (kW/L) 3.5 >5 1.5 Cost ($/kW peak) 15 <7 8 Efficiency (%) >90 at 35% to 100% maximum speed >93 at 10% to 100% maximum speed aThe targets are based on a series power train with 30-kW continuous power and 55-kW peak power. Entries for 2003 are taken from AIPM and automotive electric motor drive (AEMD) specifications. bTechnical targets include the gearbox and connectors. SOURCE: FCVT, 2004. alternatives through an advanced R&D program whose salient elements are the development of silicon carbide (SiC)-based converters and high-temperature capacitors. The Semikron inverter is being retrofitted with SiC diodes, and a number of research programs at different organizations are directed toward higher temperature capacitors. New thermal management techniques applicable to both the electronics and the motor are being explored. The EE technical team is pursuing the development of an integrated motor controller chip. The preliminary design was completed in October 2004 and testing was to have occurred in December 2004. The vision is that such integration will reduce system costs. The FreedomCAR and Fuel Partnership and INEEL have benchmarked the commercially available DLCs and identified their potential for HEVs (see discussion of DLCs in the section on electrical energy storage). Oak Ridge National Laboratory (ORNL) has done a detailed analysis of the Toyota Prius second-generation hybrid motor to evaluate its design and performance and the processes used in its manufacture. A very preliminary analysis of the Prius drive electronics has also been performed, with a more detailed analysis of performance and construction planned for the near future. To the committee’s knowledge, the results of these analyses have not yet been used for guidance in the specification or design of the FreedomCAR vehicle EE components.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report Assessment of the Program The EE component of the FreedomCAR program is addressing a diversity of challenges. Development programs are spread among national laboratories, universities, commercial contractors, and the three automotive companies (OEMs). The particular problems being addressed by these organizations appear to be well defined and relevant to the FreedomCAR and Fuel Partnership goals. The quality of these activities and their results to date are also good, though several of them are in the early stages. While all these activities are addressing important EE issues, a process for coordinating their output to address systemic Partnership goals was not apparent in either the presentations or written material provided to the committee. This will be no small task given the diversity and large number of activities. Of particular interest will be the benchmarking of FreedomCAR EE developments against both the components and the integrated systems of the Toyota Prius. For example, since the Prius’s physical and performance characteristics are similar to those of the FCHEV, many of the metrics for the latter should be similar to those for the Prius—for example, thermal performance, cost, efficiency, and energy/power densities. Toyota has invested considerable resources in the continuing redesign of the Prius motors and power electronics, and the FreedomCAR program should exploit this investment to its advantage. The results of the ORNL benchmarking exercise should be used to help establish the starting point for the EE technical team’s more aggressive research agenda and goals. Since electronic controls serve as the interface for all the subsystems in the FCHEV, coordination among the technical teams to assure that the interfaces are correctly defined is crucial for system integration. To date the interaction among the technical teams has been informal and infrequent. The quarterly meetings among technical team chairs and the USCAR FreedomCAR directors address operational issues, not the tactical issues necessary for specifying interface tasks. There is an all-technical-team meeting every other year, but this relaxed schedule cannot achieve the coordination needed. Given its central role at the interfaces, the EE technical team should probably serve as the catalyst for the coordination process. Furthermore, it is not clear to the committee that progress in one area that has implications for the specifications or parameters in other areas is communicated to or recognized by those other areas. Recommendations The interfaces among the many subsystems in the FCHEV are not only critical to safe and proper vehicle operation but also may contribute significantly to vehicle cost, and the committee is concerned that this issue is not receiving adequate attention.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report Recommendation. The EE technical team should play a leading role in coordinating the specifications for the interfaces among the many vehicle subsystems, using established standards where they exist and accelerating the development of new ones where they are needed. Recommendation. The EE technical team should identify the R&D path leading to the motor cost goal, or it should reassess that goal. Recommendation. The EE technical team should use its evaluation of the state of the art of HEV technology to update and establish the team’s future research agenda and goals. Recommendation. The EE technical team should develop a process for coordinating the diverse activities it is overseeing. Recommendation. Integrating the electronics with the motor may well provide significant cost advantages. The EE technical team should consider these potential advantages and extend Table 3-6 to include aggressive targets for an integrated system in 2010 and 2015. Recommendation. High-temperature power electronics and advanced thermal management systems will significantly impact the size, weight, cost, and reliability of the EE subsystems. FreedomCAR work in this area appears to be limited to the application of SiC devices to the Semikron inverter. The EE technical team should be aware of and leverage the work on high-temperature semiconductors, packaging, and thermal management being funded by government agencies at universities, commercial organizations, and the national laboratories. STRUCTURAL MATERIALS Vehicle programs designed to achieve major fuel economy improvements must incorporate significant weight savings. The widespread application of light-weight materials and innovative manufacturing processes are necessary to attain this goal. The FreedomCAR and Fuel Partnership has set a vehicle weight reduction target of 50 percent, adding the criterion “affordable cost.” These objectives in weight and cost are not dissimilar to those in the predecessor PNGV program and thus allow continuation of the materials programs already in place. Perhaps more important, the same materials technical team is in place to continue these efforts, which have been under way for a number of years, without major perturbations in objectives or content. These programs were reviewed extensively by the NRC Standing Committee to Review the Research Program of the PNGV Program in its seventh report (NRC, 2001). The current review of the FreedomCAR and Fuel Partnership will concentrate on the relevance and ad-
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report equacy of the overall materials programs rather than the specific details of individual programs, which were covered in the previous PNGV report. Material Thrusts Virtually all of the important materials programs in place when the FreedomCAR program was initiated have been continued. In summary, the programs consist of R&D on materials known to be capable of producing very significant weight savings when applied extensively throughout the vehicle structure—namely, high-strength steels, aluminum alloys, and carbon-fiber-reinforced polymer (CFRP) composites. In addition, work on the selective application of cast aluminum alloys, cast magnesium alloys, aluminum metal matrix composites, and titanium alloys is under way. Owing to the lower densities (except HSS), all these materials achieve the weight savings, but usually at a very significant cost penalty compared with current materials. Thus, while there are some major technical obstacles to the extensive application of these lightweight materials, the paramount challenge to the program is achieving cost parity, or “affordability.” The difficulty of achieving affordability cannot be overemphasized, and all the large research programs should include a roadmap showing how to reach the cost target. HSS structures are probably the closest to approaching affordability but are only likely to achieve about half of the targeted weight reduction. As documented in the last NRC review of the PNGV program, there is an extensive program under way in the steel industry to maximize weight savings in body structures through optimal use of HSS and innovative manufacturing practices (NRC, 2001). This program, known as the Ultralight Steel Auto Body-Advanced Vehicle Concept (ULSAB-AVC), adequately covers HSS development and capability. Additional research on HSS within the FreedomCAR and Fuel Partnership does not appear to the committee to be necessary. The NRC report recommended that the materials technical team closely monitor the ULSAB-AVC program, not only for the potential use of HSS but for the possible transfer of innovative (weight-saving) manufacturing processes to other low-density materials, in particular aluminum alloys (NRC, 2001). The current committee enthusiastically endorses this recommendation. The only current competitors to HSS for extensive vehicle applications are aluminum alloys and CFRP composites. These material families are capable of meeting the overall weight-saving target, but their cost penalty is large. While not minimizing the manufacturing difficulties associated with both classes of materials, it is the cost of the feedstock material that will most seriously prevent widespread application. In the case of aluminum alloys, previous projects for demonstrating lower cost feedstock—for example, continuous cast sheet for body structures—have not resulted in the commercial development of any such material. Similarly, CFRP composites await the arrival of low-cost carbon fibers, a holy grail that has eluded the fiber industry for decades and is unlikely to be achieved without the enthusiastic participation of large carbon fiber producers. While the current committee supports some research activities in both aluminum alloys and CFRP, greater
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report TABLE 3-7 Weight Savings for Lightweight Materials Lightweight Material Material Replaced Mass Reduction (%) Relative Cost (per part)a HSS Mild steel 10-24b 1 Aluminum Steel, cast iron 40-60 1.3-2 Magnesium Steel or cast iron 60-75 1.5-2.5 Magnesium Aluminum 25-35 1-1.5 Glass FRPc Mild steel 25-35 1-1.5 Carbon FRPc Mild steel 50-65 2-10+ Aluminum MMCd Steel or cast iron 50-65 1.5-3 Titanium Alloy steel 40-55 1.5-10+ Stainless steel Mild steel 25-40 1.2-1.7 aIncludes both materials and manufacturing costs; the lower bound of unity is a future projection. bThe lower bound is taken from Powers (2000) and the upper bound from NRC (2000). cFRP, fiber-reinforced polymer. dMMC, metal matrix composite. SOURCE: Powers, 2000. efforts to gain the cooperation of the major material manufacturers would clearly be critical to any future long-term use of these materials. In the R&D areas for more selective applications, the materials technical team reported an increasing interest in magnesium alloys based on their potential to offer major weight savings in cast applications. Programs in this arena seem very appropriate because of the low density of the materials and the significant opportunities in materials development that are necessary for successful applications. It is likely that magnesium materials will be useful only in cast applications, and these should be the focus of the FreedomCAR programs, including significant basic materials research. While the technical team expressed guarded optimism that magnesium sheet structures might have some potential, this topic would not appear to be fruitful without some major substantial participation from the raw materials industry. For reference purposes, Table 3-7, adapted from the PNGV report (NRC, 2001; Powers, 2000), illustrates the relative costs of low-density materials and associated manufacturing costs. The relative cost column indicates the potential cost penalties resulting from application of the various material technologies under consideration. Recommendations The materials technical team has the benefit of several years’ experience and obviously operates very cooperatively. It has clearly benefited from the earlier NRC reviews of the PNGV program and encompasses in its R&D portfolio all the opportunities for weight reduction afforded by current and future materials.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report Recommendation. The only FreedomCAR effort on HSS should be careful monitoring of outside programs with the objective of adopting novel manufacturing and assembly methods to aluminum structures. This recommendation mirrors the previous NRC recommendation on the PNGV program. The cost of a high-volume material such as aluminum is not likely to be reduced by federally sponsored research. Such cost reduction will be achieved only with increased application and production. Recommendation. The most important aspect of the stamped aluminum program is cost reduction, particularly for the feedstock material. Efforts in manufacturing should be limited until progress in the cost area has been achieved. The fundamental issue with CFRP composites is the development of low-cost carbon fibers. The award of a single research grant to a national laboratory does not reflect the importance of this problem. Low-cost carbon fibers would also reduce the costs of several of the hydrogen storage options. Recommendation. More extensive research programs on CFRPs, combined with the direct cooperation of the large fiber manufacturers, appear mandatory for any hope of success within the program time frame. Meanwhile, R&D for manufacturing of structures should continue. Recommendation. Longer-term research programs in magnesium alloys should be funded because of the weight savings these materials could offer. Cast materials should be the primary emphasis, with limited exploratory work on wrought materials. Increased activity in this area is highly recommended. Recommendation. The materials technical team should provide technical materials input to other technical teams—for example, electronics, the hydrogen on-board supply system, magnets, motors, fuel cell structural issues—where such input would be useful. The team has never been asked to do this, but it could be extremely useful to the overall program. Recommendation. The materials technical team should provide models of weight reduction/cost trade-offs to the systems analysis and engineering team. This would help define the singular objectives for individual systems and allow some flexibility in the focus of cost reduction efforts. Recommendation. Overall, since cost reduction is the main need in many of the materials programs, the committee suspects that research activities are of somewhat limited benefit. Thus, much of this research funding might better be ex-
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Review of the Research Program of the FreedomCAR and Fuel Partnership: First Report pended on other more challenging research areas, such as hydrogen storage materials, batteries, fuel cells, and the infrastructure. Comment on Vehicle Weight Reduction Target In the opinion of this review committee, it is extremely unlikely that a 50 percent reduction in vehicle weight (at anywhere close to cost parity) can be achieved in the 2010 to 2012 time frame without increasing vehicle costs substantially. It might be prudent for FreedomCAR to reconsider this probably unattainable target and adopt a more realistic goal–for example, a 30 percent overall weight reduction with minimal (say, <5 percent) cost penalty. The overall system objectives could either directly reflect this change, or targets in other systems areas might be adjusted in compensation. The only other alternative is to maintain the current 50 percent weight saving goal but allow for a significant cost penalty—probably unacceptable to both the automotive industry and the automotive consumer. REFERENCES Akihama, K., Y. Takatori, K. Inagaki, S. Sasaki, and A.M. Dean. 2001. “Mechanism of the smokeless rich diesel combustion by reducing temperature.” SAE paper 2001-01-0655. DOD. 2003. Residential Fuel Cell Demonstration Site Data. Available on the Web at <http://dodfuelcell.com/res/site_performance.php4>. DOE (U.S. Department of Energy). 2003. Advanced Combustion Engine R&D. 2003 Annual Progress Report. Office of Energy Efficiency and Renewable Energy. Available on the Web at <www.eere.energy.gov/vehiclesandfuels/pdfs/program/2003_pr_adv_cidi.pdf>. DOE. 2004a. FreedomCAR and Vehicle Technologies Multi-Year Program Plan. Washington, D.C.: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Available on the Web at: <http://www.eere.energy.gov/vehiclesandfuels/resources/fcvt_mypp.shtml>. DOE. 2004b. Projected Benefits of Federal Energy Efficiency and Renewable Energy Programs (FY2005-2050), Appendix J. Available on the Web at <http://www.eere.energy.gov/office_eere/pdfs/gpra_fy05/appendix_j.pdf>. DOE. 2005. Hydrogen, Fuel Cells and Infrastructure Technologies Program, Multi-Year Research, Development and Demonstration Plan. Office of Energy Efficiency and Renewable Energy. FCVT (FreedomCAR and Vehicle Technologies). 2004. The Advanced Power Electronics and Electric Machines Roadmap (April 14, 2004), EE Technical Team, FreedomCAR and Fuel Partnership. Washington, D.C.: Office of Energy Efficiency and Renewable Energy. NRC (National Research Council). 2000. Review of the Research Program of the Partnership for a New Generation of Vehicles, Sixth Report. Washington, D.C.: National Academy Press. NRC. 2001. Review of the Research Program of the Partnership for a New Generation of Vehicles, Seventh Report. Washington, D.C.: National Academy Press. Powers, W.F. 2000. “Automotive materials in the 21st century.” In Advanced Material Processes. Materials Park, Ohio: ASM International. Siebers, D.L., and L.M. Pickett. 2004. Aspects of Soot Formation in Diesel Fuel Jets. THIESEL 2004 Conference on Thermo- and Fluid Dynamic Processes in Diesel Engines. TIAX LLC. 2004. Cost Analysis of Fuel Cell Systems for Transportation, October 20, Reference D0006, SFAA No. DE-SC02-98EE50526, Topic 1 Subtopic 1C. Cambridge, Mass.: TIAX LLC.
Representative terms from entire chapter: