The role of preferential evaporation on the ignition of multicomponent fuels in a homogeneous spray/air mixture

The effect of preferential evaporation and liquid species diffusion on the ignition of multicomponent surrogate fuels in homogeneous mixtures was investigated using a developed model that considers the evaporation of a monodisperse droplet cloud in a homogeneous and isobaric gas-phase environments. After evaluation of the accuracy of individual model components against available experimental data the model was applied to study the ignition of a surrogate mixture for a Jet-A fuel (POSF 4658) at conditions of interest to gas turbine engines. The maximum reactivity occurred for conditions at which the ignition time in the gas phase was comparable to the evaporation time. At these conditions the mixture composition was greatly influenced by preferential evaporation which in turn influenced the reactivity of the gas phase. The intradroplet diffusion plays a critical role on the radial droplet composition thereby conditioning the evaporation rates of single species. A comparison with a zero-diffusivity model for the treatment of droplet internal diffusion highlighted the significance of liquid diffusion on the autoignition time and confirmed the need for properly accounting for a detailed description of multicomponent evaporation effects.