Study on the Combustion and Microexplosion of an Emulsified Fuel Droplet in High Pressure Gaseous Environments

用加热的镍铬合金丝点燃悬浮在安装在高压燃烧室中的细石英纤维尖端的乳化燃料液滴。一个CCD摄像机被提供来观察液滴火焰，并确定燃烧寿命时间和微爆炸开始的等待时间。液滴温度通过使用精细热电偶测量。采用平面激光散射技术对液滴火焰中的碳烟场进行了可视化研究。利用图像分析系统对散射光强度图像的测量结果进行量化，得到烟尘浓度的二维分布。还提供了一台高速摄像机，用于拍摄微爆引起的液相相变、相分离和液滴二次雾化。以正十二烷和正十六烷为基础燃料，对油包水和水包油型乳化燃料进行了燃烧试验，结果表明，随着压力的升高，乳化燃料的燃烧寿命逐渐缩短，在超临界气体环境中，燃烧寿命趋于常数。增加压力导致最终液滴温度的增加，其低于基础燃料的饱和温度。这在高压下变得非常明显。水包油型乳化油滴在高温下发生相转变，油水层分离。一种球形水滴，悬浮在水面上，并封闭在基础燃料层中。这不是油包水乳化燃料液滴的情况。微爆仅发生在压力低于极限值时，且压力随含水量的增加而略有增加。微爆发生的等待时间随压力的增加而减小，其分布符合威布尔分布函数。液滴火焰中的最大碳烟量随着压力的增加和水含量的减少而增加。

An emulsified fuel droplet suspended at a tip of fine quartz fiber installed in a high pressure combustion chamber was ignited with a heated nichrome wire. A CCD camera was provided to observe a droplet flame and to determine the combustion life time and the waiting time for the onset of microexplosion. The droplet temperature was measured by using a fine thermocouple. A planar laser light scattering technique was employed for the visualization of soot field in the droplet flame. The measured results of the image of scattered light intensity were quantified by using an image analyzing system to obtain the two dimensional profile of soot concentration. Also provided was a high speed video camera for the photographic observation of the phase transition, phase separation in the liquid phase and the secondary atomization of droplet due to microexplosion. Tested were water-in-oil and oil-in water emulsified fuel with the base fuel of n-dodecane and n-hexadecane.The results showed that the combustion life time decreased with an increase in pressure, approaching a constant in supercritical gaseous environments. Increasing pressure caused an increase in the final droplet temperature which was lower than the saturated temperature of the base fuel. This became remarkable at high pressure. The phase transition and the separation of water and oil layrs was observed at high temperature of the oil-in-water emulsified fuel droplet. A spherical droplet of water suspended afloat and enclosed within the layr of base fuel. This was not the case for water-in-oil emulsified fuel droplet. The microexplosion occurred only at the pressure lower than the limit which increased slightly with increasing water content. The waiting time for the onset of microexplosion which decreased with increasing pressure was correlated with the Weibull distribution function. The maximum quantity of soot in the droplet flame increased with an increase in pressure and a decrease in water content.