Alternate Fuels

Motor vehicles are major sources of air pollutants worldwide, and the number of vehicles is anticipated to continue growing (e.g., see Walsh, 1990). A major focus of control strategy development for mobile sources in recent years has been on the development of alternate fuels. These range from relatively minor changes in the traditional composition of gasoline, such as reformulated gasolines, to compressed natural gas (CNG), liquefied petroleum gas (LPG), alcohol fuels and their blends with gasoline, or hydrogen. There have also been significant developments in electric vehicles fueled either by batteries or fuel cells.

One might expect that vehicle emissions would be related to the composition of the fuel used, and a number of studies have confirmed this (e.g., see Schuet-zle et al., 1994; Siegl et al., 1992; and Kaiser et al., 1991, 1992, 1993). For example, emissions coming from a single-cylinder engine have shown that the mass emissions increase as the molecular weight of a single-component fuel increases and that benzene emissions decrease as the aromatic content of the fuel decreases (Schuetzle et al., 1994).

Hence, a feasible control strategy should be the use of fuels with smaller mass emissions, reduced reactivity of the emissions, or both. We discuss briefly some of the chemical implications of the use of some of these alternate fuels. For a more comprehensive treatment of the advantages and disadvantages of alternate fuels and technologies, see the National Research Council report (1991), and for a discussion of a variety of issues associated with motor vehicle emissions, see Cadle et al. (1996, 1997a, 1997b) and Chang et al. (1991).

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