Analysis of transient combustion of a multicomponent liquid fuel droplet

The transient combustion of a multicomponent liquid fuel droplet has been studied. The unsteady effects caused by the liquid- and gas-phase processes are considered. The numerical results demonstrate that due to the process of fuel vapor accumulation within the inner region to the flame and to the high liquid-phase mass diffusional resistance, a situation is reached where the concentration of fuel vapor in the inner zone of the flame or in the immediate vicinity of the droplet surface exceeds that at the droplet surface for certain values of the liquid-phase Lewis number. This results in a suppression of the mass vaporization rate (i.e., negative vaporization rate) without any indication of flame extinction. The results also indicate that with the increase in the volatility differentials between the mixture constituents vaporization is suppressed earlier in the droplet lifetime. However, by decreasing the liquid Lewis number, this phenomenon can be eliminated and the complete droplet lifetime can be computed. For example, the numerical results show that for a 50-50 by mass heptane-decane droplet, a liquid-phase Lewis number larger than three results in suppression of vaporization.