Effects of natural convection on high-pressure droplet combustion

Burning behavior of a suspended fuel droplet under both normal and microgravity fields has been studied experimentally to explore the effects of natural convection at high ambient pressure levels up to four times the fuel critical pressure. The fuel employed was n-octane. Experiments have shown that the burning rate constant increases with the increase of the ambient pressure at subcritical pressures and decreases at supercritical pressures for both microgravity and normal gravity fields. The maximum value of the burning rate constant appears at the critical pressure of the fuel. The natural convection increases the burning rate constant and its effect becomes stronger as the ambient pressure increases. The natural convection effect is expressed as ( K K 0 − 1) ∼ Gr 0.25 or ( (K K 0 − 1) ∼ P 0.5 for high pressures, where Gr is the Grashof number and K and K 0 are the burning rate constants in natural gravity and microgravity fields.