共轨柴油机缸内喷雾与燃烧动态可视化试验

Dynamic visual experiment on in-cylinder spray and combustion of common-rail diesel engine

为研究电控高压共轨柴油机缸内喷雾与燃烧,以某高压共轨柴油机为样机设计了一种多功能动态可视化试验装置,采集了共轨柴油机缸内动态燃烧过程图像。在此基础上,对柴油机进气道进行改进,利用工业纯度的氮气替代新鲜空气,使柴油机在单缸不着火的条件下,实时采集缸内多次动态喷雾图像。研究表明:利用该装置可以清晰、真实地观察到电控高压共轨柴油机预喷、主喷与后喷的多次喷油时间、喷雾锥角和雾化情况。预喷发生在-25°曲轴转角时,持续期约5°曲轴转角,喷油量较少,雾化不明显;主喷发生在-10°曲轴转角时,持续时间约10°曲轴转角,喷油量大,贯穿力强,可以清晰地观察到缸内明显的油束和喷雾锥角,喷雾以直线形式向活塞顶"ω"型底部扩展;后喷发生在8°曲轴转角时,持续时间较短,喷油量较少,但由于较高的缸内温度使燃油雾化效果明显。在着火时,可以实时观测不同工况下缸内着火、火焰中心形成以及火焰传播过程。缸内着火初始,燃油离散不充分,只有部分燃油和空气混合,即所谓的预混合着火部分(-15°^-4°曲轴转角)。在上止点附近,随着空气的流动使得火焰迅速扩散而充满整个燃烧室。对比额定工况下缸内燃烧图像,怠速工况下着火时刻推迟约5°曲轴转角,火焰占有面积较小,亮度较低。该研究为合理组织电控共轨柴油机缸内喷雾与燃烧提供大量的缸内信息与试验测量手段,可以对柴油机缸内喷雾与燃烧模拟计算结果进行试验验证。

In order to conduct research on the in-cylinder spray and combustion of an electrically controlled high pressure common-rail diesel engine, taking one high pressure common-rail diesel engine as the research object, a multifunctional dynamic visual experimental device was designed, which was used to collect in-cylinder dynamic combustion process images. On this basis, the intake port of the diesel engine was improved, and the fresh air was replaced by industrial purity nitrogen, so that the real-time dynamic multiple spray images were collected under single cylinder misfiring conditions. The study illustrated that the multiple injections--pre- injection, main injection, and post injection--can be clearly observed, including at the injection time, spray cone angle, and in the atomization situation. The pre-injection occurred at the -25° crankshaft angle, and the duration was about 5° crank angle. At this stage, the quantity of fuel injection was less, and the atomization was not obvious. The main injection occurred at the -10° crankshaft angle, and the duration was about 10° crankshaft angle. There was a large amount of fuel ejected from the nozzle, and the penetration force was strong. The spray cone angle and a significant oil beam could clearly be observed, which expanded to the bottom of the piston ＂co＂ crown in line. The post injection occurred at the 8° crankshaft angle, the injection duration was shorter, and the amount of fuel injection was less, however, the atomization effect was obvious because of the higher temperature of the cylinder at this stage. In addition, when the diesel engine ignited, the flame center formation and flame propagation process could be captured in real time under different working conditions. The fuel spray was not fully discrete and mixed with air partly at the initial in-cylinder ignition time, which was the so-called pre-mixing ignition and occurred at -15°- -4° crankshaft angle. Near the TDC, the flame quickly spread and filled the combustion chamber fully along with the air flowing. Compared with the in-cylinder combustion image under rated conditions, the ignition time under idling conditions was delayed about 5° crankshaft angle, the flame occupied area was smaller, and there was lower brightness. The study provided a lot of in-cylinder information and experimental measurement means for research on the in-cylinder spray and combustion of an electronically controlled common-rail diesel engine, and the spray and combustion simulation results could also be verified by these experiments.