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

为了研究湍流混合对喷雾点火过程的影响，发展了一种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。测定了十六烷的着火延迟期，并通过离子流监测、紫外、可见光和近红外光谱检测以及高速摄影等手段观察了十六烷的着火过程。主要结果如下。(1)表观活化能在1180 K、0.85MPa下发生根本变化，在高温侧和低温侧分别为170 kJ/mol和31.6kJ/mol。(2)在高温侧，点火延迟与母液滴的加热和蒸发无关，而受入射激波后液滴破碎或剥落产生的微雾的气相化学反应控制。(3)气相化学反应以火焰前反应开始。 ...更多信息 n伴随OH自由基发射和离子流，发展为蓝色火焰，伴随可见光发射。光的发射随后与稀薄风扇引起的对流相抵消。(4)高温侧的表观活化能为170 kJ/mol，与同向或垂直喷入的结果相近。而低温侧的31.6kJ/mol接近于在热滞止气氛中喷射喷雾的数据或在液滴柱受到二次流扰动时的激波管数据。(5)如果温度降低，则由于入射冲击减弱而产生的微雾的量减少，使得发光强度显著降低。在1280 K以下，没有出现高速摄影可成像的发光火焰块，而在1060 K以下，失火率迅速增加。(6)湍流混合对液滴柱的点火过程有很大的影响，因为当液滴柱受到来自排液管或雾化器安装管的二次流扰动时，其点火过程完全不同。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