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在柴油机燃烧过程的数学模拟中,燃油喷雾蒸发过程的模拟是非常重要的一环。一般地说,燃油的雾化和蒸发本来就是一个十分复杂的现象,在内燃机中,由于过程的瞬态性质(全过程为毫秒量级),问题变得更加复杂。但许多现有的柴油机喷雾模型都对这一非常复杂的过程作了大量的简化。例如在一些有代表性的喷雾模型中,有的根本没有考虑蒸发(和栗模型),有的假设燃油喷入气缸后全部立即汽化(米尔顿、邱的模型),有的采用单滴稳态蒸发公式计算蒸发量、隐含地假设了油滴进入气缸后会立即达到平衡温度(拉玆列采夫、盛宏至的模型)。以上模型显然都没有考虑油滴蒸发初始阶段的特点。金国栋的模型考虑了油滴蒸发初始段,但假设在初始段努赛数Nu=2,意味着忽略了油滴和气体间的相对速度,在阿德勒和林等的模型中也有类似假设。实际上,恰恰在初始段中油滴和气体间的相对速度是比较大的。
In the mathematical simulation of diesel combustion process, the simulation of fuel spray evaporation process is a very important part. In general, atomization and evaporation of fuel have always been a very complex phenomenon, and in internal combustion engines the problem becomes more complicated due to the transient nature of the process (the whole process being on the order of milliseconds). However, many of the existing diesel spray models greatly simplify this very complex process. For example, in some typical spray models, some do not consider evaporation (and chestnut model) at all, others assume that the fuel is completely vaporized immediately after it is injected into the cylinder (Milton and Qiu models), and some use single-drop steady-state evaporation The formula for calculating evaporation implicitly assumes that the oil droplets reach the equilibrium temperature immediately after they enter the cylinder (a model of Razaltsev, Sheng Hongzhi). Obviously none of the above models takes into account the characteristics of the initial stage of oil drop evaporation. Jin Guodong’s model takes into account the initial section of droplet evaporation, but assuming Nux = Nu in the initial stage, which means ignoring the relative velocity between oil droplets and gas, there are similar assumptions in the models of Adler and Lin et al. In fact, the relative velocity between oil droplets and gas is relatively large in the initial section.