A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle.

二冲程发动机没有移动的阀，火花塞每次点火活塞到达循环顶端。

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Note that the compression ratios shown above reflect the expansion ratio, which is the ratio of the combustion chamber volumes when the piston is at Bottom dead centre and Top dead centre.

请注意，压缩比上述反映膨胀率，这是燃烧室的量的比例时，活塞的下死顶死中心，中心会显示。

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This pressure rise is so great that a force is exerted upon the top of the piston that is sufficient to force the piston all the way down the cylinder.

压力的大幅度升高使得作用在活塞顶部的力足够大，从而迫使活塞一直延气缸下行。

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Instead of sparking the ignition when the piston is close to top dead center (when the air is compressed), that spark occurs as the piston is pulling away, when the air pressure is at its most turbulent, creating much faster ignition and more power.

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