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

作用在火焰上的电场力和浮力都是体力，因此有可能通过施加电场来控制浮力。火焰中的体积力是引起火焰周围对流的重要因素。在这种情况下，单液滴在垂直直流电场中的燃烧行为进行了研究。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。电极之间的间距为50 mm，并且当底部电极接地时，施加的电压范围在-4kV至6 kV之间。当电场方向与浮力方向相反时，外加电压的存在使火焰在垂直方向上对称，在该电压下乙醇和正辛烷的燃烧速率常数均存在局部极小值。然而，最小燃烧速率常数大于微重力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，存在一些不能用电场只通过正离子产生体积力的假设来解释的实验结果。这表明负离子引起的附加体积力。本文还讨论了负电荷碳烟粒子的运动对甲苯火焰燃烧特性的影响。

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.