Two-stroke Cycle Engines and Pollution

For most applications, there are two major types of small combustion engine that are available: the two-stroke and four-stoke cycle engines. They differ greatly in the amount of airborne pollution they emit, especially in the form of fine particulate matter.

This is largely a consequence of the way lubricating oils are used in the combustion process. In the case of four-stroke cycle engines, the oil is contained in a separate chamber and recycled for lubrication purposes only. By way of comparison, two-stroke cycle engines, as are commonly found in lawnmowers, jet-skis and chainsaws use the oil directly in the fuel, burning it along with the gasoline.

It is thought that a single lawn mowing with a two-stroke cycle engine is responsible for emitting as much unfiltered pollution as a typical car or truck emits over the course of an entire year. The problem of unburned hydrocarbons in waterways was so bad that in the 1990s, many states and provinces banned the sale of such engines in personal watercraft.