SAE Technical Paper Series Characterization of Recent-Model High-Emitting Automobiles

In-use vehicles which are high emitters make a large contributionto the emissions inventory. It is not known, however, whether high-emitting vehicles share common emissions characteristics. We study this by first examining

laboratory measurements of second-by-second engine-out and tailpipe emissions from a small number of

MY90-97 high-emitting vehicles. We distinguish highemitter types by the behavior of six ratios in low- and

moderate-power driving: the engine-out emissions indices (engine-out pollutant to fuel-rate ratios) and the catalyst

pass fractions (tailpipe to engine-out ratios) for CO, HC, and NOx. Four general types of high emitter are

observed: 1) fuel-air ratio excessively lean, 2) fuel-air ratio excessively rich, 3) partial combustion such as misfire,

and 4) severe deterioration in catalyst performance in vehicles where malfunctions of Types 1, 2 or 3 are not

predominant. We also find that these behaviors may be chronic, or may only occur transiently. The second step

is to determine the prevalence of the four different types of high emitter in the on-road fleet. For this we analyze

IM240 tailpipe emissions from a large sample of cars measured in the Arizona inspection and maintenance

program. We find that all four types of failure are observed with roughly comparable probabilities.