Combustion behavior of single droplets for sooting and non-sooting fuels in direct current electric fields under microgravity

Abstract

This paper presents experimental results for the effects of electric fields on the combustion of singledroplets for sooting and non-sooting fuels in microgravity. The ambient gas was air at atmospheric temperature and pressure, and ethyl alcochol, n -octane, and toluene were used as fuels. Applied electric field intensities ranged between 0 and 140 kV/m. The result showed clearly that the blue flame region, which corresponds to the reaction zone, is deformed toward the negative screen in electric fields for ethylalcohol. The deformation of luminous flames occurred for n -octane and toluence and is associated with the behavior of carbonaceous soot particles. The burning rate constant increased with an increase in the electric field intensity for all of the fuels tested. We suppose that induced flow to the negative screen exists by the movement of the positive ion molecules in electrc fields, and the induced flwo velocity was estimated using the analogy of flame displacement in forced convection. The burning rate constant in electric fields was predicted by the well-known empirical equation of burning rate constant in forced flows. For ethyl alchol and n -octane, experimental results are nearly consistent with predictions, while the measured burning rate constant is larger than the predicted results for toluence. The shadowgraph showed the reduction of the amount of soot that existed in the flame by electric fields for toluence, which results in the reduction of radiative heat loss of the flame. It is believed that this leads to an additional increase in burning rate constant in electric fields for toluene.