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Difference between revisions of "Two stroke"
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[[Image:2-stroke moped smoking.jpg|200px|thumb|right|2-stroke [[moped]] smoking]] | [[Image:2-stroke moped smoking.jpg|200px|thumb|right|2-stroke [[moped]] smoking]] | ||
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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[[Image:Arbeitsweise Zweitakt.gif|thumb|left|550px|A two-stroke engine, in this case with a [[tuned pipe|tuned expansion pipe]] illustrating the effect of a reflected pressure wave on the fuel charge. This feature is essential for maximum charge pressure (volumetric efficiency) and fuel efficiency. It is used on most high-performance engine designs.]] | [[Image:Arbeitsweise Zweitakt.gif|thumb|left|550px|A two-stroke engine, in this case with a [[tuned pipe|tuned expansion pipe]] illustrating the effect of a reflected pressure wave on the fuel charge. This feature is essential for maximum charge pressure (volumetric efficiency) and fuel efficiency. It is used on most high-performance engine designs.]] | ||
Although the principles remain the same, the mechanical details of various two-stroke engines differ depending on the type. The design types of the two-stroke engine vary according to the method of introducing the charge to the cylinder, the method of scavenging the [[cylinder (engine)|cylinder]] (exchanging burnt exhaust for fresh mixture) and the method of exhausting the cylinder. | Although the principles remain the same, the mechanical details of various two-stroke engines differ depending on the type. The design types of the two-stroke engine vary according to the method of introducing the charge to the cylinder, the method of [[scavenging]] the [[cylinder (engine)|cylinder]] (exchanging burnt exhaust for fresh mixture) and the method of exhausting the cylinder. | ||
===Reed inlet valve=== | ===Reed inlet valve=== | ||
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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]] | ||