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通过具有与实机燃烧室形状相同的可视化发动机研究小型直喷式柴油机的燃烧,观测了发动机规格(如喷油系统、燃烧室形状)对燃烧特性的影响。燃油喷束与空气的混合特性随燃烧室形状而变化。燃烧特性或受喷束与燃烧室壁相冲击的效果所左右,或受自由喷束的动量所左右。喷嘴喷孔数的增加对不同燃烧室的燃烧特性有不同的影响,在冲击起主导作用的燃烧中,它能增加各冲击喷束间的相互干扰,导致炭烟排放增加;在以自由喷束为主的燃烧中,它能改善喷束的空间分布,但当喷油压力低时令隙容积中空气的利用率变差。改变喷油嘴突出量不仅影响火焰在燃烧初期的分布与后期的流出特性,也影响火焰在燃烧室里的运动,从而产生不同的排放效果。
The effect of engine specifications (such as fuel injection system, combustion chamber shape) on combustion characteristics was investigated by testing the combustion of a small direct injection diesel engine with a visual engine of the same shape as the combustion chamber of a real machine. The mixing characteristics of the fuel jet and air vary with the shape of the combustion chamber. The combustion characteristics are either influenced by the impact of the jet and the wall of the combustion chamber, or by the momentum of the free jet. The increase of the number of nozzle orifice has different influence on the combustion characteristics of different combustion chambers. In the combustion which takes the leading role, it can increase the mutual interference between each impact jet and lead to the increase of soot emission. In the main combustion, it can improve the spatial distribution of the spray, but when the injection pressure is low, the make-up volume of air in the utilization rate of the worse. Changing the amount of nozzle protrusion not only affects the distribution of the flame in the early stages of combustion and the subsequent outflow characteristics, but also affects the movement of the flame in the combustion chamber, resulting in different emission effects.