Impact of multi-component description of hydrophilic fuel droplets in propagating spray flames

The need for an accurate description of the fuel composition is emerging in recently published studies on the interaction of droplets and flames. In this context, hydrophilic fuels are of particular importance, since they are expected to interact with the water formed during combustion reactions. The impact of such interactions onto the reaction process is still not explored enough. This work aims to contribute to the understanding of such interactions by investigating the impact of accurately describing the heat and mass transfers on hydrophilic fuel droplets interacting with flames. For that, a recently proposed phase change model is employed, demonstrated to be one of the few capable of characterizing the differential diffusion of vapor into the gas phase for hydrophilic fuels interacting with reacting flows. Numerical simulations of freely propagating flames in quiescent droplet mists are conducted with a detailed chemistry description. Different scenarios focus on the impact of water addition in the gaseous or liquid phase. Results demonstrated the multi-component phase change significantly impacts the flame speed in humid air and/or with hydrous ethanol, and neglecting this effect leads to strong miscalculation in flame speed. This is shown to be a consequence of the hydrophilic property of the chosen fuel, which allows the conversion from single-component to multi-component droplets, thus modifying the flame structure.Novelty and significance statement•Differential diffusion is rigorously accounted for with a new phase change model in flames propagating in droplet mists of a hydrophilic fuel, i.e., ethanol.•The multi-component modeling is necessary even when considering the injection of pure hydrophilic fuel.•When the multi-component description of the liquid fuel is enabled, flame speeds become higher than those values achieved with the single-component approach.•Air humidity interacts with hydrophilic fuel droplets delivering higher flame speed values.•A novel justification is presented for the observed higher flame speed values of flames propagating in droplet mists when compared to single-phase flames.