FUEL VAPOR ACCUMULATION EFFECT ON THE COMBUSTION CHARACTERISTICS OF MULTICOMPONENT FUEL DROPLETS

The effect of fuel vapor accumulation on the gasification behavior of a multicomponent fuel droplet has been investigated. Expressions for t he droplet vaporization rate, flame front standoff ratio and other qua ntities of interest have been obtained by using a formulation that con siders quasi-steady, diffusive-convective transport in the gas phase, and transient diffusive transport within the droplet. Results are pres ented for the combustion of a bicomponent heptane-decane fuel droplet. It is demonstrated that a significant amount of fuel vapor can be acc umulated in the inner zone to the flame, which has a noticeable effect on the droplet gasification behavior since the fuel consumption rate is reduced compared to the vaporization rate. This has important impli cation for spray flames using multicomponent fuel droplets, since the fuel vapor accumulation can substantially modify the rates of interpha se energy and mass transport rates, as well as the fuel vapor distribu tion in the flow field. Results also indicate that the fuel accumulati on effect, combined with the effect of high liquid mass diffusional re sistance (large Lewis number), leads to a self-sustained oscillation o f the vaporization rate. The oscillation is unique to the multicompone nt fuel droplet in that the accumulation effect does not cause any osc illation for a pure fuel droplet. The oscillatory behavior is also sup pressed for a multicomponent fuel droplet for moderate values of liqui d Lewis number with the accumulation effect, and for any values of liq uid Lewis number without the accumulation effect.