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