A life-cycle comparison of alternative automobile fuels

We examine the life cycles of gasoline, diesel, compressed natural gas (CNG ), and ethanol (C2H5OH)-fueled internal combustion engine (ICE) automobiles . Port and direct injection and spark and compression ignition engines are examined. We investigate diesel fuel from both petroleum and biosources as well as C2H5OH from corn, herbaceous bio-mass, and woody biomass. The basel ine vehicle is a gasoline-fueled 1998 Ford Taurus. We optimize the other fu el/powertrain combinations for each specific fuel as a part of making the v ehicles comparable to the baseline in terms of range, emissions level, and vehicle lifetime. Life-cycle calculations are done using the economic input -output lifecycle analysis (EIO-LCA) software; fuel cycles and vehicle end- of-life stages are based on published model results. We find that recent advances in gasoline vehicles, the low petroleum price, and the extensive gasoline infrastructure make it difficult for any altern ative fuel to become commercially viable. The most attractive alternative f uel is compressed natural gas because it is less expensive than gasoline, h as lower regulated pollutant and toxics emissions, produces less greenhouse gas (GHG) emissions, and is available in North America in large quantities . However, the bulk and weight of gas storage cylinders required for the ve hicle to attain a range comparable to that of gasoline vehicles necessitate s a redesign of the engine and chassis. Additional natural gas transportati on and distribution infrastructure is required for large-scale use of natur al gas for transportation. Diesel engines are extremely attractive in terms of energy efficiency, but expert judgment is divided on whether these engi nes will be able to meet strict emissions standards, even with reformulated fuel. The attractiveness of direct injection engines depends on their bein g able to meet strict emissions standards without losing their greater effi ciency. Biofuels offer lower GHG emissions, are sustainable, and reduce the demand for imported fuels. Fuels from food sources, such as biodiesel from soybeans and C2H5OH from corn, can be attractive only if the co-products a re in high demand and if the fuel production does not diminish the food sup ply C2H5OH from herbaceous or woody biomass could replace the gasoline burn ed in the light-duty fleet while supplying electricity as a co-product. Whi le it costs more than gasoline, bioethanol would be attractive if the price of gasoline doubled, if significant reductions in GHG emissions were requi red, or if fuel economy regulations for gasoline vehicles were tightened.