被动预燃室汽油机当量燃烧特性的数值分析

Numerical Analysis of the Stoichiometric-Combustion Characteristics of A Gasoline Engine with A Passive Pre-Chamber

对一台被动预燃室增压直喷汽油机的燃烧过程进行了三维数值模拟分析,研究了预燃室的不同设计参数如预燃室容积、射流孔数量、射流孔直径、射流孔结构等对当量燃烧时燃烧特性的影响。结果表明,预燃室射流点火优于常规火花塞点火的重要原因是主燃烧室内着火点增多,同时点火后预燃室内产生的高速冲击射流会提升主燃室内的湍流强度,从而加快湍流火焰的传播。在2000 r/min转速和1.2 MPa平均指示有效压力工况下预燃室发动机的50%燃烧角相对火花塞发动机提前约8.5°。不同结构参数的预燃室模拟分析表明燃烧初期预燃室喷入主燃室射流的动量越大,对主燃室湍流强度的提升效果会越大,燃烧相位也会更优,在上述工况下不同结构预燃室50%燃烧角的差异最高可达约5.8°。变更预燃室结构造成的燃烧相位差异主要体现在燃烧前中期,随着转速和负荷升高,该差异有降低的趋势。

The three-dimensional numerical simulation analysis of the combustion process was carried out in a turbocharged direct-injection gasoline engine with a passive pre-chamber.The effects of different design parameters of the pre-chamber,such as the volume of the pre-chamber,the number of the jet orifices,the diameter of the jet orifices,and the structure of the jet orifices,on the stoichiometric-combustion characteristics were studied.The results show that the main reason why jet ignition of the pre-chamber is superior to the conventional spark ignition is that the number of ignition spots in the main combustion chamber is increased,and the high-speed jet generated from the pre-chamber after ignition will enhance the turbulence intensity in the main combustion chamber,thereby accelerating the propagation of the turbulent flame.Under the engine operation condition of 2000 r/min and 1.2 MPa indicated mean effective pressure(IMEP),the 50%fuel-burnt angle of the pre-chamber engine is about 8.5°ahead that of the spark ignition engine.From the simulations of different pre-chamber structural parameters,it is found that the stronger the momentum of the jet injected from the pre-chamber into the main combustion chamber at the initial stage of combustion,the greater the enhancement effect on the turbulence intensity in the main combustion chamber and the better the combustion phases.The 50%fuel-burnt angles among various structured pre-chamber cases differ up to nearly 5.8°under the engine operation conditions mentioned above.The differences in combustion phases caused by the varied pre-combustion chamber structures are mainly reflected in the early and middle combustion stages,and these differences tend to decrease as the engine speed and load increase.