Two-stroke engine
internal combustion engine type
A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston, one up and one down, in one revolution of the crankshaft in contrast to a four-stroke engine which requires four strokes of the piston in two crankshaft revolutions to complete a power cycle. During the stroke from bottom dead center to top dead center, the end of the exhaust/intake (or scavenging) is completed along with the compression of the mixture. The second stroke encompasses the combustion of the mixture, the expansion of the burnt mixture and, near bottom dead center, the beginning of the scavenging flows.
Two-stroke engines often have a higher power-to-weight ratio than a four-stroke engine, since their power stroke occurs twice as often. Two-stroke engines can also have fewer moving parts, and thus are cheaper to manufacture and weigh less. In countries and regions with stringent emissions regulation, two-stroke engines have been phased out in automotive and motorcycle uses. In regions where regulations are less stringent, small displacement two-stroke engines remain popular in mopeds and motorcycles. They are also used in power tools such as chainsaws and leaf blowers. SSG and SLG glider planes are frequently equipped with two-stroke engines.
History
The first commercial two-stroke engine involving cylinder compression is attributed to Scottish engineer Dugald Clerk, who patented his design in 1881.
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