Insights into near nozzle spray evolution, ignition and air/flame entrainment in high pressure spray flames
Insights into near nozzle spray evolution, ignition and air/flame entrainment in high pressure spray flames
复制标题
DOI：
10.1016/j.fuel.2021.120383
复制
发表时间：
2021-06
期刊：
影响因子：
7.4
通讯作者：
Madan Mohan Avulapati;R. Pos;T. Megaritis;L. Ganippa
中科院分区：
文献类型：
--
作者：
Madan Mohan Avulapati;R. Pos;T. Megaritis;L. Ganippa
在六孔共轨柴油机喷油器中，通过实验研究了高压喷油器早期形成的动力学过程及其对点火、局部烟尘形成和夹带以及喷雾间相互作用的影响。这些喷雾火焰测量使用超高速成像技术，在反应高压环境下保持光学可达的定容腔中进行。从燃料液滴获得的反向散射光和宽带自然煤烟亮度图像及其分析揭示了在高喷射压力下燃料喷雾早期发展过程中径向分散如何影响柴油喷雾火焰的点火、火焰稳定和煤烟形成的新见解。对高速数据的分析表明，在靠近喷嘴的燃料喷雾发展的早期阶段，径向扩散（本文称之为凸起）就发生了。被困在这些凸起中的精细分散的燃料液滴云失去了它的瞬间，相对于喷雾的液体核心迅速蒸发，形成局部可燃的混合物，并从这些位置开始点火。从这些局部点火点形成的局部火焰核往往发展成小袋的烟尘火焰，随后向喷嘴方向逆主喷雾移动，并被夹带到喷雾的液芯中。有时，当凸起很大时，这些烟袋也被运送到下一次喷雾中。向喷嘴输送并进入液体喷雾芯的烟尘火焰在其与液体喷雾芯的相互作用下熄灭。淬灭火焰中含有丰富的未燃烃和烟尘颗粒，通过改变燃油喷雾核心内的等效比，有可能对污染物的形成产生重大影响。在形成凸起的过程中，观察到大小的差异很大，并且在多孔喷射器的不同孔口的喷雾之间也存在差异。这些异常主要与影响喷雾早期发展的喷嘴囊流动的复杂性有关。
Experimental investigations were performed to study the dynamic processes related to early development of high pressure sprays and their effects on ignition, local soot formation and its entrainment as well as spray to spray interactions in a six-hole common rail diesel injector. These spray-flame measurements were performed using ultra-high speed imaging technique in an optically accessible constant volume chamber maintained under reactive high pressure environment. The acquired back scattered light from fuel droplets and the broadband natural soot luminosity images and their analysis have revealed new insights on how the radial dispersions of fuel sprays during its early development at high injection pressures affect the ignition, flame stabilisation and soot formation in diesel spray flames.Analysis of the high speed data have shown that radial spreading also called as bulge in this paper occurs during the very early stages of fuel spray development closer to nozzle. The cloud of finely dispersed fuel droplets trapped within these bulges loses its moment and evaporates quickly relative to liquid core of the spray to form a locally ignitable mixture and this initiates ignition from these locations. Local flame kernels formed from these local ignition sites tend to develop into small pockets of sooting flame, which subsequently moves counter to the main spray towards the nozzle and gets entrained into the liquid core of spray. At times, these sooting pockets are also transported to into the next spray when the bulges are large. The sooting flames that are transported towards the nozzle and into the liquid spray core are quenched upon its interaction with the core of liquid spray. Quenched flames are rich in unburnt hydrocarbon and soot particles and they have the potential to significantly impact the pollutant formation through altering the equivalence ratio within the core of fuel spray. Wide variations in the sizes were observed on the formation of bulges, and it also varied between sprays from different orifices of a multi-hole injector. These anomalies are mainly related to the complexity of nozzle sac flow affecting the early spray development.