A study on single fuel droplets combustion in vertical direct current electric fields

Both the electric force working on flames and the natural buoyancy are body forces, so there is a possibility to control the natural buoyancy by applying than 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 electric fields was investigated. Ethanol, n-octane, and toluene were used as fuels, and the flame shape and the burning rate constants were measured. The distance between electrodes is 50 mm, and the applied voltage ranged between −4 and 6 kV as the bottom electrode is ground. When the direction of the electric field is opposite to the natural buoyancy direction, the applied voltage exists that make the flame symmetrical 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 electric force roughly balances with natural buoyancy, but it does not completely balance with the same. When the direction of the electric field is in the same direction as the natural 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 negative charged soot particles on the combustion behavior are also discussed for the sooty flame of toluene.