A numerical study of polydisperse spray flame ignition and extinction fronts in a mixing layer

Abstract

A new numerical study of laminar polydisperse flame ignition and extinction fronts in a mixing layer resulting from opposed streams of fuel and oxidant is presented. Two quite different initial droplet size distributions having the same Sauter mean diameter (SMD) are considered. The phenomenon of hysteresis is found to occur for a high initial droplet load but disappears as the latter decreases. The range of strain rate values for which hysteresis is prevalent depends on the initial size distribution. For example, whilst under certain operating conditions, an extinction front may result from using one initial droplet size distribution, use of another size distribution, even having the same SMD, can exhibit hysteresis. Other features of the influence of the initial spray polydispersity are discussed in depth.

Keywords:

• polydisperse spray
• spray flame
• ignition front
• extinction front
• mixing layer

Acknowledgements

LSK and GIS gratefully acknowledge the support the Israel Science Foundation (Grants 335/13) and the Binational Science Foundation (Grants 2012-057). JBG thanks the Technion Fund for the Promotion of Research and the Lady Davis Chair in Aerospace Engineering supporting this research.

Notes

¹All three cases for and Δ = 10 demand a significantly finer grid (1600 × 1600 points) for simulation than others, which were performed on 400 × 400 or 800 × 800 points grids.