Spray Flames in an Air-Heptane Swirling Combustor

Abstract

Three-dimensional n-heptane spray flames in a model swirl combustor are investig ated by means of direct numerical simulation to provide insight into spray evaporation and combustion in realistic combustors. The variable-density, low-Mach number Navier-Stokes equations are solved using a fully conservative finite difference scheme in cylindrical coordinates. Dispersed droplets are tracked in the Lagrangian framework. The droplet evaporation process is described by an equilibrium model and the vapor combustion is modeled using an adaptive one-step reaction. The results show that the vortex and flame structures are quite complex. The effect of different parameters, including the equivalence ratio, co- or counter-swirling, and inflow conditions are analyzed and are found to influence the fluid dynamics and fl ame structures. It is also found that the spray combustion is characterized by lean premixed, rich premixed, and diffusion flames, and stabilized by different mechanisms in this geometry. Furthermore, premixed flam es are found to contribute more than diffusion flames to the total heat release rate, though their appearanc e seems to be less. An unsteady flamelet model is also proposed to account for the influence of evaporation on c ombustion.