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Difference between revisions of "Two stroke"
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A '''Two stroke''' engine differs from the [[four stroke]] engine by completing the four strokes of intake, compression, combustion, exhaust in only two strokes of the piston rather than four. This is done by using the beginning of the compression stroke and the end of the combustion stroke to perform the intake and exhaust functions. This allows a power stroke for every revolution of the crank, instead of every second revolution as in a four stroke engine. | A '''Two stroke''' engine differs from the [[four stroke]] engine by completing the four strokes of intake, compression, combustion, exhaust in only two strokes of the piston rather than four. This is done by using the beginning of the compression stroke and the end of the combustion stroke to perform the intake and exhaust functions. This allows a power stroke for every revolution of the crank, instead of every second revolution as in a four stroke engine. | ||
Two stroke engines provide high specific power for lightweight [[motorcycle]]s as well as chainsaws. An example of a large application is locomotive engines of the 1800-1900s. Most designs use total-loss lubrication, with the oil being burnt in the combustion chamber, causing "blue smoke" and other types of exhaust pollution. This is the major reason for two-stroke engines being replaced with four-stroke engines in most applications. | Two stroke engines provide high specific power for lightweight [[motorcycle]]s as well as chainsaws. An example of a large application is locomotive engines of the 1800-1900s. Most designs use total-loss lubrication, with the oil being burnt in the [[combustion chamber]], causing "blue smoke" and other types of exhaust pollution. This is the major reason for two-stroke engines being replaced with four-stroke engines in most applications. | ||
Dugald Clark is attributed with inventing the two stroke cycle around 1880. His engines had a separate charging cylinder. Joseph Day is credited with the "crank case" scavenged engine using the area below the piston as a charging pump. Frederick Cock is credited for the piston controlled inlet port engine. | Dugald Clark is attributed with inventing the two stroke cycle around 1880. His engines had a separate charging cylinder. Joseph Day is credited with the "crank case" scavenged engine using the area below the piston as a charging pump. Frederick Cock is credited for the piston controlled inlet port engine. | ||
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===Crossflow-scavenged=== | ===Crossflow-scavenged=== | ||
In a crossflow engine the transfer ports and exhaust ports are on opposite sides of the cylinder and a deflector on the top of the piston directs the fresh intake charge into the upper part of the cylinder pushing the residual exhaust gas down the other side of the deflector and out of the exhaust port. The deflector increases piston's weight and its exposed surface area, and also makes it difficult to achieve an efficient combustion chamber shape. This design has been largely superseded by loop scavenging method (below), although for smaller or slower engines the crossflow-scavenged design can be an acceptable approach. | In a crossflow engine the transfer ports and exhaust ports are on opposite sides of the cylinder and a deflector on the top of the piston directs the fresh intake charge into the upper part of the cylinder pushing the residual exhaust gas down the other side of the deflector and out of the exhaust port. The deflector increases piston's weight and its exposed surface area, and also makes it difficult to achieve an efficient [[combustion chamber]] shape. This design has been largely superseded by loop scavenging method (below), although for smaller or slower engines the crossflow-scavenged design can be an acceptable approach. | ||
==See Also== | ==See Also== | ||
* [[Rotary Disc Valve]] | * [[Rotary Disc Valve]] | ||