Effect of Fuel Injection Rate Shaping on Intermittent Spray Combustion

通过开发和使用一种新颖的电控燃油喷射系统，研究了喷油规律对间歇喷雾和燃烧的影响。(1)可变喷油率成形燃油喷射系统的研制：该系统采用压电陶瓷驱动器直接控制喷油针的运动，实现任意喷油率成形。通过使用大功率致动器，注射压力高达100 MPa，在这项研究中实现。(2)单次喷射的影响：在相同的喷油周期、峰值喷油率和总喷油量条件下，研究了不同喷油压力下三角形喷油率成形和不同喷油率上升斜率的喷雾。结果表明，喷油率上升斜率对喷雾的时间演化、喷雾火焰的着火和主燃烧有很大影响。较高的喷射压力促进了喷雾的生长，促进了燃烧，特别是在燃烧初期。这些趋势导致所有喷射率成形的燃烧期较短。从缩短燃烧期的角度出发，最佳喷油规律随喷油压力的变化而变化。(3)两级喷射的影响：研究表明，喷射间隔对第二级喷射的喷雾演化和整个燃烧过程有很大的影响。这些影响随着第二级喷射的喷射速率的变化而变化。(4)注射速率周期性波动的影响：检查了注射速率以相对较高频率周期性波动的影响。从可视化实验中可以清楚地看出，在某些特定的频率下，喷雾分散变得更宽。在周期性波动的喷雾中，稠密液核中喷射出大量的燃料液滴，液核长度在上述频率下变得很短。

By developing and using an original electronically controllable fuel injection system, effect of injection rate shaping on intermittent spray and combustion was studied.(1) Development of Fuel Injection System for Variable Injection Rate Shaping : In our system, the arbitrary injection rate shaping was obtained by controlling the movement of nozzle needle directly with piezoelectric actuator. By using a high power actuator, injection pressure of up to 100MPa was achieved in this study.(2) Effect in Single Injection : At the same conditions of injection period, peak injection rate and total amount of fuel injected, the spray with triangular injection rate shaping and different slope of injection rate rise for some injection pressures was examined. It was found that the slope of injection rate rise made great influences on the temporal evolution of the spray, the ignition and main combustion of the spray flame. Higher injection pressure enhanced the growth of spray and promoted the combustion especially at initial stage. These tendencies result in a shorter combustion period for all injection rate shaping. From the viewpoint of shorter combustion period, the optimum fuel injection rate shaping changes with injection pressures.(3) Effect in Two Stage Injection : It was made clear that the injection interval gives a large effect on the spray evolution of 2nd stage injection and overall combustion. These effects change with the injection rate shaping of 2nd stage injection.(4) Effect of Periodical Fluctuation of Injection Rate : Effect of periodical fluctuation of injection rate with relatively higher frequency was examined. From the visualized experiments, it was made clear that the spray dispersion becomes wider at some specified frequencies. In the spray with periodical fluctuation, a large cloud of fuel droplets was ejected from the dense liquid core and the length of liquid core becomes very short at above mentioned frequencies.