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。

youdao

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。

youdao

In some application, a narrow groove is cut into the piston above the top ring to serve as a "heat dam" to reduce the amount of heat reaching the top ring.

在一些实际结构中，一条窄槽切入顶端活塞环的上部，其作用是充当“隔热槽”以减少达到顶端活塞环的热量。

youdao

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.

FORBES: How To Get 50 MPG Out Of Your Gasoline Engine