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本文利用激光阴影法和气体模拟方法研究了中小缸径直喷式柴油机受限喷雾特性.实验发现燃烧室壁面对油束发展的干涉对柴油机燃空混合过程具有重要影响.当油束与壁面撞击时,出现一个强化紊流混合的过渡过程.此时喷雾锥角增大,空气卷吸率提高.当油束沿壁面发展时,存在很大的近壁浓度梯度,但由于近壁区域低紊流强度和低浓度脉动,油束在垂直于壁面方向上扩散率比空间油束径向扩散率低得多,使浓混合气集中于壁面,形成相对稳定浓混合气堆积.壁喷出现之后,喷射诱导的气流运动在油束周围形成环涡运动,环涡运动抑制空气与燃烧产物的混合,使产物高温持续时间加长,NO_x排放增加.
In this paper, laser shadowing and gas simulation were used to study the limited spray characteristics of small and medium bore direct injection diesel engines. It was found that the combustion chamber wall interference on the development of oil bundles had an important effect on the combustion-air mixture process. , A turbulent mixing transition occurs, the spray cone angle increases, and the air entrainment rate increases.When the oil bundles develop along the wall, there is a large gradient of near-wall concentration, but due to the low turbulence Intensity and low concentration pulsation, the diffusivity of the oil bundles perpendicular to the wall direction is much lower than the radial diffusivity of the space oil bundles, so that the concentrated gas concentrates on the wall surface to form a relatively stable rich gas accumulation. After the wall sprays emerge, the jet Induced airflow motion creates a ring-eddy motion around the oil bundle. The eddy motion suppresses the mixing of air and combustion products, prolonging the duration of high-temperature products and increasing NOx emission.