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 2-20 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. © 2004 IMechE.