On the Structure of Unconfined Turbulent Spray Flames

Abstract

Computations are reported on the detailed structures of unconfined turbulent combusting sprays. Favre-averaged gas-phase equations and a κ-ε-g turbulence closure model are utilized. Using a conserved scalar approach and assuming the form of probability density function to be a clipped Gaussian, the thermodynamic scalar variables are calculated from a partial equilibrium model. The major features of the liquid-phase model are that a stochastic random-walk approach is used to represent the effect of gas-phase turbulence on droplet trajectories and vaporization. variable-property effects are considered in a comprehensive manner, and a conduction-limit model is employed to represent the transient liquid-phase processes. This two-phase model is used to study the structure of an unconfined methanol spray flame. An important observation is that the turbulent spray flame structure is significantly different, both quantitatively and qualitatively, from that of the corresponding gaseous diffusion flame. In addition, the spray flame exhibits a strong sensitively to transient liquid-phase processes. The latter result is interesting since, in an earlier computational study for an evaporating spray, the vaporization behavior for the same liquid fuel indicated only a weak sensitivity to these processes.