由于排汽凸轮盘不正确的定时或排汽系统背压过大（背压不能超过300毫米水柱）而导致燃气通过扫气口倒流。

C. Blow-back through the scavenge air ports, owing to an incorrectly adjusted exhaust cam disc or large resistance in the exhaust system(back pressure not exceed 300 mm wc)

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扫气道的设计原则是尽可能减少新鲜充量向排气口的短路损失。

The principle of scavenging port designing is to minimize short circuit losses resulting from the fresh air flowing to the scavenging port.

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本文即是采用数值模拟的方法，研究在其它条件不变的情况下，柴油机结构对扫气效率的影响，以期达到指导柴油机气口结构设计的目的。

This thesis's purpose is to study the affect on the efficiency of the structure of the diesel engine with anything else fixed and to direct the design of the diesel's port structure.

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