Proceedings of the Combustion Institute ( IF 3.4 ) Pub Date : 2020-11-12 , DOI: 10.1016/j.proci.2020.09.004 M.A. Shahbaz , N. Jüngst , R. Grzeszik , S.A. Kaiser
In direct-injection spark-ignition engines, fuel films formed on the piston surface due to impinging sprays are a major source of soot. Previous studies investigating the fuel films and their correlation to soot production were mostly performed in model experiments or optical engines. These experiments have different operating conditions compared to commercial engines. In this work, fuel films and soot are visualized in an all-metal engine with endoscopic access via laser-induced fluorescence (LIF) and natural incandescence, respectively. Gasoline and a mixture of isooctane/toluene were used as fuel for the experiments. The fuel films were excited by 266 nm laser pulses and visualized by an intensified CCD camera through a modular UV endoscope. Gasoline yielded much higher signal-to-noise ratio, and this fuel typically took an order of magnitude longer to evaporate than isooctane/toluene. The effects of injection time, injection pressure, engine temperature, and combustion on the fuel-film evaporation time were investigated. This film survival time was reduced with higher engine temperature, higher injection pressure, and later injection time, with engine temperature being the most significant parameter, whereas skip-fired combustion had very little effect on the film survival time. In complementary experiments, LIF from fuel films and soot incandescence were simultaneously visualized by an intensified double-frame CCD camera. At lower engine temperatures the fuel films remained distinct, and soot formation was limited to regions above the films, whereas at higher temperatures, fuel films, and hence the soot, appeared to be spread over the whole piston surface. Finally, high-speed imaging showed the spray, chemiluminescence, and soot incandescence, with results broadly consistent with fuel-film LIF and soot incandescence imaging.
中文翻译:
直喷式火花点火发动机中的内窥镜燃料膜,化学发光和烟尘白炽成像
在直接喷射式火花点火发动机中,由于冲击喷雾而在活塞表面上形成的燃料膜是烟灰的主要来源。先前对燃料膜及其与烟灰产生的关系进行调查的研究大多是在模型实验或光学引擎中进行的。与商用发动机相比,这些实验具有不同的运行条件。在这项工作中,可通过激光诱导荧光(LIF)和自然白炽灯在内窥镜访问的全金属发动机中可视化燃料膜和煤烟。汽油和异辛烷/甲苯的混合物用作实验燃料。燃料膜被266 nm激光脉冲激发,并通过模块化CCD内窥镜通过增强的CCD相机进行可视化。汽油产生更高的信噪比,而且这种燃料蒸发所需的时间通常比异辛烷/甲苯要长一个数量级。研究了喷射时间,喷射压力,发动机温度和燃烧对燃料膜蒸发时间的影响。较高的发动机温度,较高的喷射压力和较晚的喷射时间会缩短膜的生存时间,其中发动机温度是最重要的参数,而跳过燃烧对膜的生存时间影响很小。在补充实验中,来自燃料膜的LIF和烟尘白炽现象通过增强的双框CCD相机同时可视化。在较低的发动机温度下,燃料膜仍保持清晰,并且烟灰的形成仅限于膜上方的区域,而在较高的温度下,燃料膜以及因此的烟灰,似乎散布在整个活塞表面上。最后,高速成像显示了喷雾,化学发光和烟灰白炽灯,其结果与燃料膜LIF和烟灰白炽灯成像大致一致。