Effect of Variable Properties in Modeling the Spray Droplet Burning in Mixed Convective Environment

Abstract

In the present study, a numerical methodology for solving the set of transient governing equations in axi-symmetric cylindrical coordinates describing fuel droplet combustion has been developed. Both an infinite and a finite rate chemistry model have been used. The former utilizes a simple definition of mixture fraction along with thermo-physical properties evaluated at an averaged temperature. The latter utilizes a global single step reaction with five species and Arrhenius type of rate equation. Thermo-physical properties in this case have been evaluated as functions of temperature. These models have been used to analyze burning of a single fuel droplet in a mixed convective environment. A detailed parametric study has been carried out by varying the free-stream velocity and ambient temperature. Numerically predicted flame shapes and mass burning rates have been validated with porous sphere experimental results available in literature for the case where the ambient temperature is 300 K. The ability of infinite rate chemistry model for predicting the characteristics of diffusion flames to reasonable accuracy at low ambient temperature (300 K) has been established. At higher ambient temperatures, the results from the infinite rate chemistry model are shown to vary considerably from finite rate chemistry model as well as the experimental results.