Total Fuel Cycle Impacts of Advanced Vehicles 1999-01-0322
Recent advances in fuel-cell technology and low-emission, direct-injection spark-ignition and diesel engines for vehicles could significantly change the transportation vehicle power plant landscape in the next decade or so. This paper is a scoping study that compares total fuel cycle options for providing power to personal transport vehicles. The key question asked is, “How much of the energy from the fuel feedstock is available for motive power?” Emissions of selected criteria pollutants and greenhouse gases are qualitatively discussed. This analysis illustrates the differences among options; it is not intended to be exhaustive. Cases considered are hydrogen fuel from methane and from iso-octane in generic proton-exchange membrane (PEM) fuel-cell vehicles, methane and iso-octane in spark-ignition (SI) engine vehicles, and diesel fuel (from methane or petroleum) in direct-injection (DI) diesel engine vehicles. We also consider advanced hybrid technology to develop an upper bound for vehicle efficiency realizable using internal combustion engines (ICEs). Future-technology fuel-cell vehicles and future-technology hybrid ICE vehicles (particularly those with direct-injection engines) have similar projected ranges of efficiency. Differences, if any, will only become apparent after fuel-cell and advanced ICE vehicles are ready for market testing. The main challenge for fuel-cell vehicles is to improve the efficiency of hydrogen production (off-board and on-board). The main challenge for ICE hybrid vehicles is to meet stringent new emission standards while maintaining high efficiency. Both fuel-cell and ICE hybrid technologies require a reliable and efficient hybrid powertrain, and both would benefit from cleaner, lower-sulfur fuels, as well as advanced catalysts for improved fuel production and/or exhaust aftertreatment. The greenhouse gas (GHG) emissions ranking approximately corresponds to the total fuel-cycle efficiency ranking. Fuel-cell vehicles are excellent candidates for carbon emissions reductions if methane is the preferred feedstock. The GHG benefits of petroleum feedstock for fuel-cell vehicles are less certain relative to advanced hybrid ICE vehicles. Emissions of criteria pollutants from fuel-cell vehicles are expected to be near zero, but upstream emissions of these fuel chains are significant and will not change vs. conventional engine technology. For policy decisions, low emissions of criteria pollutants from fuel-cell vehicles and their less certain GHG and fuel economy benefits (relative to direct-injection hybrid electric vehicles) must be weighed against their earlier state of development. Similarly, unless fuel processing, combustion, and aftertreatment technologies are much improved, the fuel economy and GHG emissions benefits of advanced internal-combustion engines may not be realized as a consequence of new, much tighter emission standards for nitrogen oxides and particulates.