A Study on a Droplet Combustion Behavior in a Simulated Microgravity condition by Electric Fields

作用在火焰上的电动力和浮力都是体力，所以可以通过施加电场来控制浮力。讨论火焰中的体力是很重要的，因为它会引起火焰周围的对流。在这种情况下，研究了单个液滴在垂直直流电场中的燃烧行为。以乙醇、正辛烷和甲苯为燃料，测量了火焰形状和燃烧速率常数。底电极接地时，电极间距为50 mm，外加电压范围为-4~6kV。当电场方向与浮力方向相反时，存在使火焰在垂直方向对称的外加电压，在该电压下，乙醇和正辛烷的燃烧速率常数存在局部极小值。但最小燃烧速率常数大于微重力条件下的最小燃烧速率常数。这意味着微浮力条件可以通过电场来实现，但它不是无浮力。当电场方向与浮力方向相同时，有一些实验结果不能用电场只通过正离子感生体力的假设来解释。这表明额外的体力是由负离子引起的。对于甲苯碳烟火焰，还讨论了带负电荷的碳烟颗粒运动对燃烧行为的影响。

Both the electric force working on flames and the buoyancy are body fore, so there is a possibility to control the buoyancy with applying the electric field. It is important to discuss the body force in the flame because it induces the convective flow around flames. In this circumstance, combustion behavior of single droplets in vertical direct current (DC) electric fields was investigated. Ethanol, n-octane, and toluene were used as fuels, and the flame shape and the burning rate constant were measured. The spacing between the electrodes is 50mm and the applied voltage ranged between -4kV and 6kV as the bottom electrode is ground. When the direction of the electric field is opposite to the buoyancy direction, the applied voltage exists that make the flame symmetry in the vertical direction, and the burning rate constants have local minima for ethanol and n-octane at the voltage. However, the minimum burning rate constants are larger than those under microgravity. This means that the micro-buoyancy condition can be accomplished by the electric fields, but it is not no-buoyancy. When the direction of the electric filed is same direction of the buoyancy, there exist some experimental results which cannot be explained by the assumption that electric field induces the body force only through the positive ions. This suggests that the additional body force is induced by the negative ions. The effects of the movement of negative charged soot particle on the combustion behavior are also discussed for sooty flame of toluene.