kaksitoimiseen

Kaksitoimiseen is a Finnish term that translates to "two-stroke" in English, commonly referring to a type of internal combustion engine. Unlike a four-stroke engine, a two-stroke engine completes its power cycle in just two piston strokes and one crankshaft revolution. This is achieved by combining the intake and compression strokes into one, and the power and exhaust strokes into the other.

The fundamental difference lies in the port system. Instead of valves, two-stroke engines use ports in the cylinder wall that are covered and uncovered by the piston as it moves. During the upstroke, the piston moves towards the cylinder head, compressing the fuel-air mixture above it. Simultaneously, a vacuum is created in the crankcase, drawing in a fresh fuel-air mixture through an intake port. As the piston nears the top, the spark plug ignites the compressed mixture.

The resulting explosion drives the piston downwards, performing the power stroke. As the piston moves down, it uncovers the exhaust port, allowing burnt gases to escape. Shortly after, it uncovers the transfer port, which allows the fresh fuel-air mixture from the crankcase to rush into the cylinder, pushing out the remaining exhaust gases and preparing for the next cycle. This design leads to a simpler construction with fewer moving parts, making two-stroke engines lighter and more powerful for their size compared to four-stroke engines. However, they are often less fuel-efficient and produce higher emissions due to the inherent loss of unburnt fuel through the exhaust port. They are commonly found in applications like motorcycles, chainsaws, and outboard motors where their power-to-weight ratio is advantageous.