To keep the engine temperature in balance, a cooling system is necessary.

为保持发动机温度平衡，就必须有冷却系统。

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If the engine temperature is too high, the pistons would expand and could not move in the cylinders.

如果发动机温度太高，活塞就会膨胀，也就不能再汽缸里运动。

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NOx is produced when the nitrogen from the air reacts with oxygen under high engine temperature and pressure conditions.

在高温高压下，空气与氧气反应，产生了氮氧化物。

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One is exhaust gas recirculation, which pumps cooled exhaust back into the engine air intake, lowering the combustion temperature and reducing NOx formation.

FORBES: Clearing the Air

The EPA engineers came up with a formula that automakers around the world have long been groping for--an engine that explodes fuel at such a relatively low temperature (below 2, 000 degrees Fahrenheit) that almost no noxious nitrogen oxides are produced.

FORBES: EPA, Inc.

The board also confirmed the right engine experienced a surge during a flight on January 13, and subsequent repairs included the replacement of a temperature probe.

CNN: Investigators find feather, other evidence on downed plane