Numerical and Theoretical Analysis of Laminar Counterflowing Spray Flames for Use in Turbulent Combustion Modeling

The paper presents a combined theoretical and numerical study of laminar counterflow mono-disperse spray flames. The numerical model includes a similarity transformation of the two-dimensional governing gas phase equations into a one-dimensional formulation. The reduced computational time enables the use of detailed chemical reaction mechanisms to study the spray flame structure. In particular, the effect of spray evaporation on combustion is investigated by means of numerical simulations. For this purpose, the transport equation of the scalar dissipation rate of the mixture fraction is derived, where the spray evaporation source term is included. Numerical simulations of laminar liquid and gaseous ethanol and combustion products mono disperse spray flames under fuel-rich conditions are presented and discussed. The parametric dependence of the flame structures on strain rate is studied with emphasis on the spray evaporation. Droplet reversal and oscillation are found to dominate the flame structure, and they determine the location of the main reaction zone as well as the profile of the scalar dissipation rate. The study aims to develop a novel spray flamelet model for use in the numerical simulations of turbulent spray combustion with particular emphasis on flameless conditions.