The crown diameter of eutectic al Si alloy piston has increased suddenly in twice, but the hyper eutectic al Si alloy piston only once.
共晶铝硅合金活塞顶部直径有两次突然长大，而过共晶铝合金活塞仅有一次。
A piston engine is said at best to be only 33% efficient.
一台活塞式发动机被充其量说只成为有效率33%。
Only small aircraft, and those needing tough low-speed propulsion at low altitudes, for agricultural work and fire-fighting, still have piston engines.
只有一些小型的飞机，以及那些用于在低空低速爬升飞行的用于农业以及灭火用途的飞机仍然使用活塞发动机。
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