In order to investigate the influence of charge temperature on the combustion and nitrogen oxide ( NOx ) emission of a medium speed diesel engine under Miller cycle, three-dimensional computational fluid dynamic mod-eling was performed to simulate the in-cylinder flow, spray, combustion and NOx formation processes.The simula-tion results showed that, as the charge temperature decreases, the ignition delay, peak heat release rate of premixed combustion stage, and maximum pressure rise rate continuously increase, especially, at the point when the charge temperature decreases 40 K or more lower than that of the original engine.However, the indicated spe-cific fuel consumption rates and NOx emission rates both decrease first and then increase.The results indicated that the overly lowered charge temperature is not beneficial to the reducing of NOx emission, because the excessively prolonged ignition delay results in too much heat released in the premixed combustion stage, which accelerate the formation of thermal NOx .%为了研究米勒循环条件下充量温度的变化对某中速柴油机燃烧和 NOx排放的影响，采用三维计算流体动力学模拟方法对其缸内流动、喷雾、燃烧和NO x生成过程进行了数值模拟分析。结果表明：随着充量温度的降低，着火滞燃期、预混合燃烧放热率峰值和最高压力升高率不断增加，在充量初始温度比原机降低40 K之后尤为显著；指示油耗率和NOx排放率先降低后升高，说明过低的充量温度不利于降低NOx排放，其原因是滞燃期太长，预混合燃烧放热太多，促进了热NOx生成。
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