It is the same simplicity in design, however, that causes a two-stroke engine to be less fuel-efficient and produce high specific levels of undesirable exhaust gas emissions. The only moving parts inside simple two-stroke engines are the crankshaft, the connecting rod, and the piston. Once the piston reaches the bottom of the stroke, the second stroke is completed and the process is repeated. The transfer ports act as a passage through which the air-fuel mixture moves from the crankcase into the cylinder above the piston. Shortly after the exhaust port is uncovered by the downward travel of the piston, the transfer ports begin to be uncovered. The piston then moves downward, where the air-fuel mixture remains from the previous intake-compression stroke. As the piston passes the midpoint of the downstroke, the exhaust port to the side of the cylinder is uncovered and initiates the flow of burned fuel out into the expansion chamber or muffler through the manifold. The burnt fuel creates pressure in the cylinder above the piston and forces it downward. The power stroke begins after the air-fuel mixture is ignited. The second stroke begins once ignition has taken place.
As the piston reaches the top of the cylinder, the mixture in the cylinder is compressed to the point of ignition. As the piston continues travelling upward, transfer ports and the exhaust ports are closed off, thus trapping the combustible mixture in the combustion chamber. In a two-stroke engine, one of the two strokes combines the intake stroke and the compression stroke, while the other stroke combines the combustion stroke and the exhaust stroke.Īs the piston travels upward in the cylinder, it creates low pressure area in the crankcase this draws fresh air and atomized fuel from the carburetor through a hole in the cylinder wall or directly into the crankcase.
#Valve timing diagram of 2 stroke engine pdf full#
Operation of a two-stroke engine Ī stroke is the action of a piston travelling the full length of its cylinder. The two-stroke power valve system is an improvement to a conventional two-stroke engine that gives a high power output over a wider RPM range.
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