Higher engine efficiency and ever stringent pollutant emission regulations are considered as the most important challenges for today's automotive industry. Fast evaporation and combustion technique has caused unprecedented attention due to its potential to solve both of the above challenges. Flash boiling, which features a two-phase flow that constantly generates vapor bubbles inside the liquid spray is ideal to achieve fast evaporation and combustion inside direct-injection (DI) gasoline engines. In this study, three spray conditions, including liquid, transitional flash boiling and flare flash boiling spray were studied for comparison under cold start condition in a spark-ignition direct-injection (SIDI) optical gasoline engine. Optical access into the combustion chamber includes a quartz linear and a quartz insert on the piston. In separate experiments, we recorded the crank angle resolved spray morphology using laser scattering technique, and distribution of fuel before ignition employing laser induced fluorescence technology, as well as time-resolved color images of flame with high-speed camera. The spray morphology during the intake stroke shows stronger plume-plume and plume-air interaction under flash boiling condition, as well as smaller penetration. Then around the end of compression (before ignition), the fuel distribution is also shown to be more homogeneous with less cyclic variation under flash boiling. Finally, from the color images of the flame, it was found that with the increase of superheat degree, the diffusion rate of blue flame (generated by excited molecules) is higher, which is considered to be related with the larger fractal dimension of the flame front. Also, the combustion is more complete with less yellow flame under flash boiling.

更高的发动机效率和越来越严格的污染物排放法规被认为是当今汽车工业面临的最重要挑战。快速蒸发和燃烧技术由于具有解决上述两个挑战的潜力而引起了空前的关注。闪蒸沸腾具有两相流，可在液体喷雾内部不断产生蒸气气泡，是在直喷（DI）汽油发动机内实现快速蒸发和燃烧的理想选择。在这项研究中，研究了三种喷射条件，包括液体喷射，过渡闪蒸和火炬闪蒸喷射，以在火花点火直接喷射（SIDI）光学汽油机的冷启动条件下进行比较。进入燃烧室的光学通道包括一个线性石英管和一个位于活塞上的石英管插件。在单独的实验中，我们使用激光散射技术记录了曲柄角分辨的喷雾形态，并使用激光诱导的荧光技术记录了点火前的燃料分布，并使用高速相机记录了火焰的时间分辨彩色图像。进气冲程期间的喷雾形态表明，在闪蒸条件下，羽流与羽流之间的相互作用更强，渗透性更小。然后，在压缩即将结束时（点火之前），在快速沸腾下，燃料分布也显示出更均匀且循环变化较小。最后，从火焰的彩色图像中发现，随着过热度的增加，蓝色火焰（由受激分子产生）的扩散速率更高，这被认为与火焰前缘的较大分形维数有关。另外，在快速沸腾下燃烧较少，黄色火焰较少，燃烧更加完全。