Late-evaporating liquid fuel wall-films are considered a major source of soot in spark-ignition direct-injection (SIDI) engines. In this study, a direct-injection model experiment was developed to visualize soot formation in the vicinity of evaporating fuel films. Isooctane is injected by a multi-hole injector into the optically accessible part of a constant-flow facility at atmospheric pressure. Some of the liquid fuel impinges on the quartz-glass windows and forms fuel films. After spark ignition, a turbulent flame front propagates through the chamber, and subsequently sooting combustion is detected near the fuel films. Overlapping laser light sheets at 532 and 1064 nm excite laser-induced fluorescence (LIF) of polycyclic aromatic hydrocarbons (PAH) -potential soot precursors- and laser-induced incandescence (LII) of soot, respectively. The 532 nm light sheet has low fluence to avoid the excitation of LII. The LII and LIF signals are detected simultaneously and spectrally separated on two cameras. In complementary line-of-sight imaging, the fuel spray, chemiluminescence, and soot incandescence are captured with a high-speed color camera. In separate experiments, toluene is added to the isooctane as a fluorescent tracer and excited by pulsed 266 nm flood illumination. From images of the LIF signal, the fuel-films’ thickness and mass evolutions are evaluated. The films survive the entire combustion event. PAH LIF is found in close vicinity of the evaporating fuel films. Soot is found spatially separated from, but adjacent to the PAH, both with high spatial intermittency. Average images additionally indicate that soot is formed with a much higher spatial intermittency than PAH. Images from the color camera show soot incandescence earlier and in a similar region compared to soot LII. Chemiluminescence downstream of the soot-forming region is thought to indicate the subsequent oxidation of fuel, soot, and PAH.

较晚蒸发的液体燃料壁膜被认为是火花点火直喷（SIDI）发动机中烟尘的主要来源。在这项研究中，开发了直接喷射模型实验以可视化蒸发燃料膜附近的烟灰形成。异辛烷通过多孔注入器在大气压下注入恒定流量设备的光学可及部分。一些液体燃料撞击在石英玻璃窗上并形成燃料膜。火花点火后，湍流的火焰锋传播通过燃烧室，随后在燃料膜附近检测到烟灰燃烧。532和1064 nm处的重叠激光片分别激发多环芳烃（PAH）-潜在烟灰前体-的激光诱导荧光（LIF）和烟灰的激光诱导白炽度（LII）。532 nm的光片通量低，可避免激发LII。同时检测LII和LIF信号，并在两台摄像机上进行光谱分离。在互补的视线成像中，使用高速彩色摄像机捕获燃油喷雾，化学发光和煤烟白炽灯。在单独的实验中，将甲苯作为荧光示踪剂添加到异辛烷中，并通过脉冲266 nm泛光照明激发。从LIF信号的图像中，可以评估燃料膜的厚度和质量演变。薄膜在整个燃烧过程中均能幸存。在蒸发的燃料膜附近发现了PAH LIF。发现煤烟在空间上与多环芳烃分离，但与多环芳烃相邻，且两者具有很高的空间间歇性。平均图像还表明，与PAH相比，形成的烟灰具有更高的空间间歇性。彩色摄像机的图像显示出烟灰白炽化的时间更早，并且与烟灰LII处于相似的区域。烟灰形成区域下游的化学发光被认为指示燃料，烟灰和PAH的后续氧化。