Effect of gravity on onset of microexplosion for an oil-in-water emulsion droplet

Abstract

Microgravity combustion experiments have been carried out for an emulsion droplet suspended at a quartz fiber by free-fall method. Attention was mainly paid to the effect of gravity on the occurrence of microexplosion that may be caused by the bubble nucleation at temperatures below the superheat limit. The oil-in-water emulsion consisted of the base fuel and water was employed after degasification. The base fuel employed was n -dodecane and n -tetradecane. The water content was 0.2 in volume. The waiting time for the onset of microexplosion was measured for about 30 runs under normal gravity and microgravity. The onset probability of microexplosion was discussed from the statistical point of view by using the weakest link destruction model. The results showed that the distribution function of the waiting time correlated with the mixed Weibull distribution for both gravity conditions. That is, the distribution function is classified to the wear-out type at the initial heating period, and it is classified to the chance failure type at constanttemperature period. The change in the type of Weibull distribution occurs slightly earlier under normal gravity than microgravity for both base fuels. The Weibull distribution of the waiting time at constant-temperature period for normal gravity is almost the same as that for microgravity. The dependence of the onset rate of microexplosion on the superheating of water is independent of the gravity condition.