EFFECT OF FUEL STRUCTURE ON EMISSIONS FROM A SPARK-IGNITED ENGINE .3.OLEFINIC FUELS

A single-cylinder, production-type engine has been run at four operati ng conditions on four olefinic fuels (ethylene, 1-butene, 1-hexene, an d diisobutylene) and two blends (n-hexane with toluene and 20% diisobu tylene with a fully blended gasoline). Engine-out hydrocarbon (HC) emi ssions (total and species), NO(x), CO, and CO2 have been measured. Tot al HC emissions from the olefinic fuels increase with the molecular we ight of the fuel (e.g., from 320 ppm C1 for ethylene to 1420 ppm C1 fo r diisobutylene during lean operation). The HC emission for each olefi n is lower, and the NO(x) emission is higher than that of the correspo nding alkane. 1,3-Butadiene is significant for the straight-chain term inal olefins, 1-butene and 1-hexene, but is much less important for th e highly branched olefin, diisobutylene. For the diisobutylene-gasolin e blend, the mole fractions of products unique to diisobutylene combus tion can be predicted to within 10% based on data from diisobutylene, gasoline, and the concentration of diisobutylene in the blend. Thus, t he exhaust emissions are approximately additive. For the hexane-toluen e blend, no appreciable formation of alkyl-substituted toluenes is obs erved.