An Investigation into the Ignition Phenomena of Sprays Using a Shock Tube

为了阐明湍流混合对喷雾着火过程的影响，发展了一种利用超声雾化器产生的自由下落液滴柱在反射激波后点火的技术。测定了十六烷的点火延迟期，并通过离子电流监测、紫外、可见光和近红外光谱检测以及高速摄影观察了点火过程。主要研究结果如下：(1)当激波压力为0.85 Mpa时，表观活化能在1180K发生根本性变化，即高温侧为170kJ/m o l，低温侧为31.6kJ/m o l.(2)在高温侧，点火延迟与母液滴的加热和蒸发无关，而是由入射激波后液滴破碎或剥落所产生的微雾的气相化学反应所控制.(3)气相化学反应开始于火焰前的…反应更多的氮伴随着OH自由基的发射和离子流，成长为蓝色火焰，并伴随着可见光谱的发射。(4)高温侧的表观活化能为170kJ/mol，接近于同时或垂直于热流中注入喷雾的数据。而低温侧的31.6kJ/mol则接近于在热滞大气中喷雾得到的数据，或者在液滴柱受到二次流扰动的情况下的激波管数据。(5)如果温度降低，由于入射激波的减弱，微雾的产生量会减少，从而使发光强度大大降低。在1280K以下没有出现高速摄影能拍摄到的发光火焰团，失火率在1060K以下迅速增加。(6)湍流混合对液滴柱点火过程有相当大的影响，因为在液滴柱被来自排水管和雾化器安装管的二次流扰动的情况下，观察到了完全不同的点火过程。较少

Aiming at elucidating the effects of turbulent mixing on the ignition process of a spray, a technique was developed in which a freely falling droplets column produced by an ultrasonic atomizer was ignited behind a reflected shock. The ignition delays of cetane were determined, and the ignition processes were observed by monitoring ion current, detecting spectroscopically the light emission in UV-, visible- and near IR-bands and by the high-speed photography. The principal results were summarized as follws.(1) The apparent actrivation energy changes radically at 1180K for 0.85MPa; i.e., 170kJ/mol and 31.6kJ/mol, respectively, on the high- and low-temperature sides.(2) On the high-temperature side, the ignition delay is independent of the heating-up and evaporation of mother droplets, and governed by the gas-phase chemical reaction of the micromist generated by the shattering or peeling of droplets behind the incident shock.(3) The gas-phase chemical reaction starts as a preflame reactio … More n accompanied by OH radical emission and ion current, growing into a blue flame accomanied by visible-band emission. Hte light emission therafter synchronizes with the convections due to rarefaction fans.(4) The apparent activation energy of 170kJ/mol on the high-temperature side is close to the data obtained by injecting sprays into a hot stream concurrently or perpendicularly. whereas the one of 31.6kJ/mol on the low-temperature side is close to the data obtained by injecting sprays into a hot stagnant atmosphere or the shock tube data in case the droplets column is disturbed by the secondary flows.(5) If the temperature is lowered, the amount of micromist generated decreased due to the weakened incident shock so that the intensity of light emission decreases considerably. No luminous flame lump, imageable by the high-speed photography, appears below 1280K, and the rate of misfiring increases rapidly below 1060K.(6) It is supposed that turbulent mixing has a considerable effects on the ignition process of droplets column, since a completely different ignition process was observed in a situation that the droplets column is disturbed by the secondary flows from the drain tube or the atomizer installing tube. Less