A two-stroke engine is an internal combustion engine
that completes the process cycle in one revolution
of the crank shaft compared to two revolutions
for a four-stroke engine. Two-stroke engines
are used mostly with the smallest and largest reciprocating
power plants and less commonly with the medium sized.
Two-stroke engines are simple, lighter and feature
a higher power-to-weight ratio and low manufacturing
cost. A two stroke engine is able to generate
1.6...1.7 times greater power than a four-stroke engine
of the same volume. It is also possible to have
a smooth rotation with a small number of cylinders.
The downsides of two stroke engines are emissions
and eciency. A clear disadvantage of a two
stroke engine is the gas exchange process, especially
in the cheapest design with crank case scavenging.
The intake process suers low eciency mostly due to shortness in eective strokes. Mean eective pressure
and eciency are low mostly due to the long
opening of the exhaust.