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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*, 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 Cj for ethylene to 1420 ppm Ci for diisobutylene during lean operation). The HC emission for each olefin is lower, and the NO* 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.

An exhaust gas quenching experiment was conducted to study the evolution of HC emissions and the extent of HC oxidation in the exhaust port and runner of a spark ignition engine. Fuel composition and engine parameter effects were of particular interest. The fuel set consisted of gasoline, several alkanes (methane, ethane, propane, n-butane, iso-octane), an alkene (ethene) and an aromatic (toluene); all fuel composition experiments were completed at a light load condition. The engine parameter set included engine speed, load, spark timing, equivalence ratio and coolant temperature; experiments involved mostly single parameter variations about a light load condition.The cylinder-exit HC emissions varied significantly over the set of fuels tested. There was no significant fuel dependency in the percentage of HC oxidation in the exhaust port/runner system, which ranged from 35 to 45%. A substantial portion of the oxidation occurred in the exhaust port. Speciated HC emissions identified unburned fuel as the major cylinder-exit species. The unburned fuel contribution ranged from 80 to 95% for methane, ethene and toluene and from 40 to 70% for the non-methane alkane fuels.Changes in the species distributions for the non-methane alkane fuels were observed in both the port and runner. Alkenes, the most reactive species in the formation of photochemical smog, were the dominant non-fuel species. Hence, the benefit of HC oxidation was accompanied by an increase in photochemical reactivity.Independent increases in engine speed and load produced decreases in the percentage of HC oxidation in the exhaust port/runner system. Higher temperatures due to spark retard increased HC oxidation from approximately 38% at MBT to approximately 53% at 12 degrees retard. Fuel lean conditions yielded higher oxidation levels (42%) than did fuel rich conditions (27%) due to the 02 availability. There was negligible change in oxidation level over the coolant temperature range tested.

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