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.

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。

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The core of a steam engine is a cylinder that is sealed at one end and has a moving piston at the other.

蒸汽机的核心是汽缸。它一端密封，另一端有个可以移动的活塞。

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The piston is a cylindrical shaped hollow part that moves up and down inside the engine cylinder.

活塞是一个中空的圆柱体形状部件，其在发动机气缸里做上下往复运动。

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Its Variable Compression Engine can alter its compression ratio (the volume in a cylinder when the piston is up compared with the volume when it is down) from 14-1 to 8-1, depending on the circumstances.

ECONOMIST: Fuel economy