kaksitoimisen

Kaksitoiminen is a Finnish term that translates to "two-stroke" in English, commonly referring to internal combustion engines that complete a power cycle in two piston strokes and one crankshaft revolution. This contrasts with four-stroke engines, which require four strokes.

The operation of a two-stroke engine involves two distinct phases. In the first stroke, as the piston moves upwards, it draws a fuel-air mixture into the crankcase through an intake port. Simultaneously, the combustion gases from the previous cycle are compressed in the cylinder above the piston. As the piston reaches the top of its stroke, the spark plug ignites the compressed mixture, forcing the piston downwards in the second stroke. During this downward movement, the piston uncovers exhaust ports, allowing burnt gases to escape. Further down, it uncovers transfer ports, allowing the fresh fuel-air mixture from the crankcase to enter the cylinder, pushing out any remaining exhaust gases.

Two-stroke engines are known for their simplicity, fewer moving parts, and higher power-to-weight ratio compared to four-stroke engines. This makes them suitable for applications where compactness and light weight are crucial, such as in chainsaws, leaf blowers, and some smaller motorcycles or scooters. However, they typically have less fuel efficiency, produce more emissions due to the mixing of oil with fuel for lubrication, and can be noisier than their four-stroke counterparts. Lubrication is achieved by mixing oil directly with the fuel, which is then carried through the crankcase and cylinder.