基于激波结构的天然气发动机燃气高压喷射特性

Characteristics of High-Pressure Gas Jets for Natural Gas Engine Based on Shock Wave Calibration

基于纹影法对0.5、1.0和1.5,MPa共3种气源压力条件下燃气射流诱导激波的特征参数随时间的变化规律进行研究.结果表明:高压脉冲燃气喷射过程存在明显的状态变化,且实际喷射持续期明显大于控制脉宽.随气源压力增加,喷孔入口压力的上升时间增加,处于稳态的时间减小,燃气喷射的瞬态性增强,电磁阀关闭后的低压喷射时间长、减压慢.总体上,从气源到喷孔出口,燃气压力能到动能的转化效率小于50%,,3种气源压力下,出口雷诺数分布在0.5×10~5~2.5×10~5内,与柴油相比,甲烷射流的主动混合能力弱,被动混合能力强.随气源压力增加,马赫盘的宽度增加,进而使射流近场锥角增大,对燃气的湍流混合及空间分布起促进作用.

The time-varying jet induced shock wave characteristics are measured and analyzed under three origin pres- sure conditions of 0.5, 1.0 and 1.5 MPa by means of schlieren imaging method. Results show that the high pressure pulse gas injection process has obvious state change, and the actual injection duration is obviously larger than that of the control pulse width. With the increase of origin pressure, the rising time of the nozzle inlet pressure increases, and the duration of pressure balance at upstream of nozzle decreases. It promotes the transient variation of gas fuel injection. The velocity of gas pressure reduction is very low after the start of the solenoid valve closed, which leads to a very long time for low-pressure gas injection. In general, the conversion efficiency of gas pressure energy to kinetic energy is less than 50% from the gas source to the outlet of the nozzle. The Reynolds number at exit of the nozzle dis- tributes in the range of 0.5×10^5-2.5×10^5 under three origin pressure conditions. Compared with diesel spray, the active mixing ability of methane jet is weak, and the passive mixing ability is strong. With the increase of origin pres- sure, Mach disk width increases, which causes the increase of jet near-field angle and promotes the spatial distribu- tion and turbulent mixing of gas jet.