A two-stroke engine is a type of combustion engine that completes a power cycle in just two strokes of its piston (compared to the four strokes of a four-stroke engine). It is mainly used in smaller engines such as chainsaws, mopeds, and motorcycles.
In the first stroke, known as the compression stroke, the piston moves upwards, compressing the fuel-air mixture inside the combustion chamber. As the piston reaches the top, a spark from the spark plug ignites the mixture, causing a rapid expansion of combustion gases.
This expansion forces the piston downward, creating energy and performing mechanical work. At the same time, the exhaust ports are uncovered, allowing the pressurized gases to escape.
The second stroke, called the exhaust stroke, occurs when the piston reaches the bottom of its downward travel. In this phase, the exhaust ports remain open as the piston moves back up, pushing the remaining exhaust gases out of the combustion chamber.
Unlike a four-stroke engine, a two-stroke engine lacks a dedicated lubrication system. To compensate for this, oil is mixed with the fuel, providing lubrication and cooling to the engine's moving parts. This oil-fuel mixture is commonly referred to as pre-mix.
Although two-stroke engines have a simpler design and produce more power-to-weight ratio, they are known to produce more pollution and consume oil. However, advancements in technology have led to the development of cleaner and more efficient versions of two-stroke engines.
