Combustion and Evaporation of Deformable Fuel Droplets

Abstract

This study focuses on combustion and evaporation of an isolated freely deforming fuel droplet under convective flow. The droplet shape is modified by varying Weber number at moderate Reynolds numbers. A simplified chemical reaction mechanism is used for combustion modeling. The Direct Numerical Simulation (DNS) results show a net positive effect of Weber number on total evaporation rate (m˙) for both pure evaporation and combustion cases. The enhancement in m˙ for higher Weber number reaches up to 9% for combustion. A nonspherical envelope flame is observed which grows with time. The Damköhler number is higher than 1 for this flame type which leads to faster reaction rates in comparison to evaporation. Hence, the combustion process is seen to be unaffected by droplet shape. An additional comparison between 3-D and 2-D combustion results is performed to understand if 2-D studies can reflect the right physical aspects of this problem. It is found that local evaporation flux in 2-D is 42.5% lower due to lower temperature gradients near the droplet surface for the same inflow velocity. The deformation of droplet is significantly different in 2-D which affects the boundary layer development and the wake flow. This is seen to affect the flame shape at the downstream of droplet. Hence, the 2-D simulations do not recover the correct behaviors.