Combustion and Evaporation of Deformable Fuel Droplets

Abstract

\textit{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 modelling.} \textit{The Direct Numerical Simulation (DNS) results show a net positive effect of Weber number on total evaporation rate ($\dot{m}$) for both pure evaporation and combustion cases. The enhancement in $\dot{m}$ for higher Weber number reaches upto $9 \%$ for combustion. A non-spherical envelope flame is observed which grows with time. The Damk\"{o}hler 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.}