stempelmotor

A stempelmotor, also known as a two-stroke engine or two-cycle engine, is a type of internal combustion engine that completes a power cycle with two strokes of the piston during only one crankshaft revolution. This contrasts with a four-stroke engine, which requires four strokes and two crankshaft revolutions per power cycle.

The operation of a stempelmotor involves two main phases. In the first stroke, as the piston moves upwards, it simultaneously draws a fresh fuel-air mixture into the crankcase through an intake port and compresses the mixture in the cylinder above it. As the piston reaches the top of its stroke, the compressed mixture is ignited by a spark plug, initiating the power stroke.

During the second stroke, the expanding gases from combustion push the piston downwards. As the piston moves down, it uncovers exhaust ports, allowing the burnt gases to escape. Shortly after, it also uncovers transfer ports, which allow the fresh fuel-air mixture that was drawn into the crankcase during the upward stroke to be transferred into the cylinder, pushing out the remaining exhaust gases and beginning the cycle again.

Stempelmotoren are known for their simplicity of design, 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 important, such as in chainsaws, leaf blowers, and some smaller motorcycles. However, they typically have lower fuel efficiency and produce more emissions than their four-stroke counterparts due to the scavenging process, where some unburnt fuel can escape with the exhaust.