Based on in-cylinder combustion numerical simulation,the transient thermal environment around the real nozzle of a diesel engine was obtained.The fluid computational region connected the cylinder to the interior of the nozzle and the solid computational region around the nozzle portion protruded into the cylinder were established.Then the spray model and the atomization model were also set for the fuel spray ejected from the outlet of the six-nozzle injector.Aiming at the formation of the nozzle coking,the gas-liquid-solid coupled numerical simulation was carried out through the fluid-solid coupled heat transfer and embedded integrated flow field analysis method.As a result,the temperature distribution and the internal flow field characteristics of the nozzle were obtained.Results show that the nozzle's maximum temperature obtained by heat conduction is only 580 K in a complete working cycle of the diesel engine.However,this value does not exceed the coking temperature threshold.It is found that the main reason of the nozzle coking is that the high-temperature gas in the cylinder flows into the nozzle hole.It is proposed that the coking distribution inside the nozzle is determined by the flow velocity and the direction variation of the high-temperature gas surrounded the nozzle after fuel injection.%基于循环数值模拟获得某型柴油机缸内真实喷嘴结构周围的瞬态工作环境,采用流固耦合传热及嵌入式一体化流场分析方法,通过建立某型柴油机缸内与喷嘴内部连通的流体区域、喷嘴缸内部分的固体区域,设置六孔喷嘴自喷孔出口开始喷射的喷油雾化模型,开展针对喷嘴结焦成因的气、液、固多场耦合数值模拟,得到了喷嘴的自身温度分布和内部流场特性.结果表明:在柴油机完整工作循环中,喷嘴因自身导热最高仅达580 K,并未超过燃油结焦温度阈值,而缸内高温燃气冲入喷孔是喷嘴内部发生结焦的主因,喷嘴周围高温燃气在射流结束后的流速与流向变化规律一定程度上决定了喷嘴内部的结焦分布情况.
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