Flame propagation involved in vortices of supersonic mixing layers laden with droplets: Effects of ambient pressure and spray equivalence ratio

Numerical simulations are performed to analyze the dynamics of spray flame in a high convective Mach number mixing layer laden with n-decane droplets. The multi-phase reacting flow system is solved by a hybrid Eulerian-Lagrangian model, in which the supersonic mixing layer is mimicked by means of direct numerical simulation and the individual droplets are tracked by the Lagrangian point-mass model. The effects of elevated pressures until 0.5 MPa are emphasized on flame propagation. The spatiotemporal dispersion of fuel droplets are driven by large-scale vortices. The flame kernels are formed in the high-strain vortex-braids, and the flammable mixtures entrained in the vortex are found to burn from the edge to the core of the vortex until the reactants within the vortex are completely consumed. As the reacting pressure increases, the high-temperature region expands such that the behaviors of spray flames are strongly changed. The spray equivalence ratio affects the combustion characteristics. The growth of mixing layer thickness, flame structure, and reaction intensity are varied due to the competition of cooling from droplet evaporation to heat release from exothermic reactions. The present work deepens the understanding of spray flame propagation in supersonic shearing flows.