The present study optically measures the liquid spray penetration using high-speed backlight illumination imaging in a running small-bore compression-ignition engine. This imaging technique utilizes high-power LED as a light source that is reflected on the flat cylinder head surface except the vaporizing spray region. The boundary detection of this dark region is performed to calculate the spray tip penetration. The liquid spray development was visualized for 3 custom-made fuels exhibiting identical physical properties except the cetane number (CN30, CN40, and CN50) and a range of the distillation curves. Because the applicable injection timing range is more advanced for a lower cetane number fuel and vice versa, it provides an ample opportunity to discuss the effects of varying ambient gas temperature/density on the spray. For all tested conditions, the high-speed backlight illumination imaging was repeated for 30 injections. The results showed similar initial increase of the spray penetration for all tested injection timings and fuels due to the strong injection momentum. However, the later spray penetration showed a measurable variation with the maximum penetration becoming longer for both earlier and later injections off from TDC. The trends indicate increased spray penetration due to decreased mixing-limited vaporization at lower ambient gas temperature/density conditions. This was further supported by longer tip penetration for a fuel with higher distillation temperatures. The trends were successfully predicted using a transient jet mixing model employing discrete control volumes, suggesting indeed mixing-limited vaporization governs the liquid spray penetration in a small-bore engine.

中文翻译：

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小口径压缩点火发动机中使用高速背光照明成像的液体喷雾渗透测量

本研究在运行中的小口径压缩点火发动机中使用高速背光照明成像光学测量液体喷雾的渗透性。该成像技术利用大功率LED作为光源，该光源在汽化喷雾区域之外的扁平气缸盖表面上反射。执行该暗区的边界检测以计算喷嘴的穿透力。对于十六烷值（CN30，CN40和CN50）和一系列蒸馏曲线除外的三种物理性能相同的定制燃料，可以看到液体喷雾的发展情况。因为适用的喷射正时范围对于十六烷值较低的燃料更为先进，反之亦然，因此它为讨论改变环境气体温度/密度对喷雾的影响提供了充足的机会。对于所有测试条件，重复高速背光照明成像30次。结果显示，由于强劲的喷射动量，所有测试的喷射正时和燃料的喷雾渗透率初始增加相似。但是，较晚的喷雾渗透率显示出可测量的变化，对于从TDC进行的较早和较晚的注入，最大渗透率变得更长。趋势表明，由于在较低的环境气体温度/密度条件下减少了混合限制的汽化，因此喷雾渗透性增加。对于更高蒸馏温度的燃料，更长的针尖穿透力进一步支持了这一点。使用离散控制量的瞬态喷射混合模型成功预测了趋势，