Totaktsmotorer

Totaktsmotorer, or two-stroke engines, are a type of internal combustion engine that completes a power cycle with two strokes of the piston during one crankshaft revolution. Unlike four-stroke engines, they combine the intake and compression strokes into one, and the power and exhaust strokes into another. This design simplifies the engine's construction and often results in a higher power-to-weight ratio.

The two strokes are typically defined as follows. During the upward stroke, the piston moves from bottom dead center to top dead center. As it rises, it creates a vacuum in the crankcase, drawing in a fuel-air mixture. Simultaneously, the rising piston uncovers the exhaust port, allowing burnt gases to escape. As the piston reaches the top, it covers the exhaust port and then the transfer port, compressing the fuel-air mixture above it.

During the downward stroke, from top dead center to bottom dead center, the compressed mixture is ignited by the spark plug. The resulting explosion forces the piston downwards, generating power. As the piston descends, it uncovers the transfer port, allowing the fresh fuel-air mixture from the crankcase to enter the cylinder, pushing out the remaining exhaust gases. The piston then moves upwards again, repeating the cycle.

Totaktsmotorer are known for their simplicity, fewer moving parts, and ability to operate in any orientation. However, they also tend to be less fuel-efficient and produce more emissions compared to four-stroke engines due to the overlap of intake and exhaust processes, which can lead to some unburnt fuel escaping with the exhaust. They are commonly found in applications like motorcycles, mopeds, chainsaws, and small outboard motors.