高压喷射的高速直喷柴油机混合气形成及燃烧过程

为了有效组织燃烧室内气流特性,改进了车用缩口直喷高速柴油机燃烧室结构,并在此基础上基于CFD商用软件FIRE对匹配不同轨压的喷雾特性时燃烧室内气液混合流的速度场、浓度场和温度场的动态分布特性进行了仿真计算分析。研究了高速直喷柴油机的混合气形成规律,并通过试验研究了这种混合气形成特性对燃烧过程及排放特性的影响。结果表明:通过对缩口直喷燃烧室内气流特性和轨压的优化匹配,可以有效地控制燃烧过程的滞燃期、预混合燃烧比例和扩散燃烧过程,从而控制高温燃烧持续期,在保证经济性的前提下,可以有效地降低NOx和烟度排放。

Air-fuel mixture formation and combustion process of a high-speed direct-injection diesel engine with high pressure injection

The reentrant combustion chamber shape of a high-speed direct-injection vehicle diesel engine was improved to form required airflow-characteristics in the chamber. The dynamics of in-cylinder flow field, the air-fuel ratio distribution, and the temperature field were simulated by commercial CFD software FIRE for the airflow matching the fuel spray characteristics by different injection pressures. The air-fuel mixture formation of the diesel engine was studied by simulation, and the effects of the obtained mixture formation behavior on the combustion and exhaust emissions were investigated experimentally. The results showed that the ignition delay, the premixed combustion proportion and the diffusion combustion process can be controlled by optimal matching between the airflow characteristics in the reentrant combustion chamber and the fuel injection pressure, thus to control the high temperature combustion duration. The optimization can effectively reduce the NO_x and soot emissions simultaneously withoult penalty on fuel economy.