喷雾油滴粒径对柴油机NO_x生成浓度的影响

Effect of Atomized Fuel Drop Diameter on NO_x Concentration for Diesel Engine

利用KIVA Ⅱ程序模拟了柴油机的燃烧过程,计算了缸内燃油蒸发量、燃烧温度和有害物质NOx的生成浓度。计算结果表明,当油滴粒径较小时,缸内温度变化平缓,高温区主要集中在喷油嘴附近;在油滴粒径增加的过程中,缸内逐渐出现明显的不均匀燃烧现象,产生了局部高温区,另一方面,局部高温区空气卷入量的不同,从而导致NOx排放量随着油滴粒径的增加而出现先增后减的变化趋势。

The chemically reactive fluid flows with sprays in the combustion chamber are simulated by means of KIVAⅡ code for directinjection diesel engine. The fuel vapor quantity,combustion temperature and NOx concentration are calculated by changing the size of the nozzle hole. The simulation results show that the combustion temperatures vary gently with the high temperature areas concentrated near nozzle when the fuel drops are small. However, inhomogeneous combustion occurs in the cylinder and local high temperature area is produced when the fuel drops turn bigger. On the other hand, the air quantity entangled into the high temperature area is different according to combustion temperature. Hence,NOx emission increases first and then decreases as the fuel drops become larger.