A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the topof 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。
2
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。
3
This pressure rise is so great that a force is exerted upon the topof the piston that is sufficient to force the piston all the way down the cylinder.