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

作用在火焰上的电作用力和浮力都是体前的，因此有可能通过施加电场来控制浮力。讨论火焰中的体力是很重要的，因为它引起了火焰周围的对流流动。在这种情况下，研究了单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，测定了火焰形状和燃烧速率常数。电极间距50mm，下电极接地，施加电压在-4kV ~ 6kV之间。当电场方向与浮力方向相反时，施加的电压使火焰在垂直方向上对称，乙醇和正辛烷的燃烧速率常数在该电压下有局部最小值。然而，最小燃烧速率常数比微重力下的燃烧速率常数大。这意味着电场可以实现微浮力条件，但不是无浮力条件。当电场方向与浮力方向相同时，存在一些不能用电场仅通过正离子诱导体力的假设来解释的实验结果。这表明额外的身体力是由负离子引起的。讨论了带负电荷的煤烟颗粒的运动对甲苯煤烟火焰燃烧行为的影响。

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.