中小缸径直喷式柴油机喷雾特性的研究

An Investigation on the Fuel Spray Characteristics in a D. I. Diesel Engine

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.

An investigation on confined fuel spray characteristics in a D. I. diesel engine was conducted by using the high speed laser shadowgraphy and the technique of gaseous simulation. The results show that the air-fuel mixing process in a D. I. diesel engine is strongly affected by the spray impingement. When the spray tip approaches the chamber wall, a transient process promoting air-fuel mixing occurs. During this process the spray angle is rapidly increased by 5-8°. However excessive impingement will form a stable layer of rich mixture with low turbulence intensity and low concentration fluctuation. The toroidal movement was also observed around the spray tip near the wall when impingement occurred. A model analysis reveals that it would hamper the combustion products mixing with air and increase NO_x emission.