最后一步是将蒸汽引入气缸，使得活塞前后推动，从而提高了发动机的速度，降低了燃料消耗。

The final step came when steam was introduced into the cylinder to drive the piston backward as well as forward, thereby increasing the speed of the engine and cutting its fuel consumption.

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以前面的例子来说，在气缸活塞和汽化器到位前，将发动机装配到摩托车架是没有意义的。

Using the example from earlier, it does not make sense to mount the engine of the bike to the frame of the bike before the pistons and carburettor are in place yet.

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对于这一点，波尔玛也赞同，并且指出，用于常规轻型飞机的活塞式发动机行不通还有其他原因：要是有水渗入气缸内，它就不能工作了。

Polmar agrees, and points out that the piston engines used in conventional light planes are ruled out for other reasons: they would fail if any water leaked into the cylinders.

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