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 operating conditions on four olefinic fuels (ethylene, 1-butene, 1-hexene, and diisobutylene) and two blends (n-hexane with toluene and 20% diisobutylene with a fully blended gasoline). Engine-out hydrocarbon (HC) emissions (total and species), NO(x), CO, and CO2 have been measured. Total HC emissions from the olefinic fuels increase with the molecular weight of the fuel (e.g., from 320 ppm C1 for ethylene to 1420 ppm C1 for diisobutylene during lean operation). The HC emission for each olefin is lower, and the NO(x) emission is higher than that of the corresponding alkane. 1,3-Butadiene is significant for the straight-chain terminal olefins, 1-butene and 1-hexene, but is much less important for the highly branched olefin, diisobutylene. For the diisobutylene-gasoline blend, the mole fractions of products unique to diisobutylene combustion can be predicted to within 10% based on data from diisobutylene, gasoline, and the concentration of diisobutylene in the blend. Thus, the exhaust emissions are approximately additive. For the hexane-toluene blend, no appreciable formation of alkyl-substituted toluenes is observed.