Speciated hydrocarbon emissions and the associated local ozone production from an automotive gasoline engine

Abstract

Concentrations of total and individual exhaust gas hydrocarbon species were measured from a contemporary automotive gasoline engine to gain insight into how an engine's operating conditions affect the combustion and post-flame oxidation processes and to estimate the ozone-forming potential of these hydrocarbons. Both the customary method of estimating maximum ozone production using maximum incremental reactivity (MIR) factors and a new method of estimating actual local ozone production (LOP) were used to quantify the harmfulness of the exhaust hydrocarbons. Depending on local atmospheric conditions, LOP estimations are about 2–10 times less than the method of maximum ozone production using MIR factors. Per unit of engine output, retarded spark timing and higher engine load reduce the LOP of catalyst-in hydrocarbons, while the air-fuel ratio does not strongly affect the LOP of catalyst-in hydrocarbons. LOP is increased during a start-up and drastically decreased by the catalytic converter, once the catalyst is heated to its operating temperature and the engine is run at stoichiometry.