Exhaust Emission Characteristics of a Small 2-Stroke Cycle Spark Ignition Engine

Abstract

<div class="htmlview paragraph">The 2-stroke cycle engine has not been subject to extensive exhaust emission research because small vehicles which commonly employ 2-stroke cycle engines are not covered by federal emission regulations. This paper reports the results of a 2-stroke engine study conducted to determine the level of the unburned hydrocarbon (HC) emission and its source. Other gas phase exhaust emissions are reported as well.</div> <div class="htmlview paragraph">Exhaust composition curves were generated from a material balance model with HCs included as a product. The calculated curves were used in the analysis of the experimental data. It was determined that 25-40% of the fuel air mixture was short-circuited to the exhaust in the scavenging process which resulted in unburned HC concentrations of 5000-1000 ppm hexane equivalent. It was found that short-circuiting is a function of load but is relatively independent of speed. Emission of carbon monoxide is highly dependent on carburetor tuning and can be reduced to less than 1% vol by tuning alone. Nitric oxide emission is low compared to uncontrolled 4-stroke engines; mass emission is less than 5 g/bhp·h at most operating conditions.</div>