Vaporization Damköhler Number and Enrichment Effects in Spray Diffusion Flames in an Oscillating Flow Field

Abstract

The sensitivity to the vaporization Damköhler number of the behavior of a coflow laminar spray diffusion flame in an oscillating flow field is investigated. Droplet grouping induced by the host gas flow oscillations is accounted for, and its effect is described through a specially constructed model for the vaporization Damköhler number that responds to the proximity of the droplets as they cluster. A formal analytical solution is developed, and the dynamics of the spray flame front shapes and thermal fields are deduced. Computed results demonstrate how strongly the vaporization Damköhler number impacts on the type of primary homogeneous flame formed and on the possible existence of multiple flame sheets as the flow field oscillates. In addition, isolated regions of high fuel vapor concentrations are produced by fuel droplet enrichment. The presence of resulting parallel fluctuating thermal fields indicates a potential impact on undesirable pollutants production.

Keywords:

• Droplet grouping
• Modeling
• Spray combustion

ACKNOWLEDGMENTS

J.B.G. acknowledges the partial support of the Lady Davis Chair in Aerospace Engineering and the Technion Fund for the Promotion of Research. Thanks are due to Yonit Mindelis for her professional and dedicated technical assistance and discerning comments on the manuscript. This research was supported by the Israel Science Foundation (Grant No. 621/11).

Notes

¹It should be recalled that γ _d is the ratio of the mass fraction of liquid fuel in the droplets to the total initial mass fraction of fuel vapor and liquid fuel. Taking the initial total fuel mass fraction to be of the order of 10⁻² implies that for the values of γ _d greater than unity obtained here, the actual mass fraction of liquid fuel will not exceed unity.