This paper is concerned with the exhaust emissions from two-stroke cycle spark ignition engines and the means being investigated to reduce them. The simple two-stroke engine has inherently low levels of NOx emissions and high levels of hydrocarbon emissions. The reasons for these emissions characteristics are explained by reference to the open literature. The two-stroke engine is used in a wide range of applications including low-cost, low-output mopeds and high-performance motorcycles. More recently there has been a resurgence of interest in the two-stroke as an alternative to the four-stroke engine for automotive use. A number of the recently reported approaches to emissions control are reviewed, including the use of exhaust oxidation catalysts in simple low-cost engines and direct fuel injection on more costly, multi-cylinder engines.
Measurement of the air-to-fuel ratio inside a passive pre-chamber of a fired spark-ignition engine