Modelling n-heptane dilute spray flames in a model supersonic combustor fueled by hydrogen

Abstract

Combustion characteristics of n-heptane dilute sprays in a model supersonic combustor fueled by hydrogen are numerically investigated. The two-phase compressible reactive flows are solved by a Eulerian-Lagrangian framework. Supersonic air enters the combustor at Mach 2.0, whereas hydrogen is injected sonically at the strut base. Monodispersed liquid n-heptane droplets are carried by hydrogen jet at different Spray Equivalence Ratios (SERs), which range from 0 to 0.096. The results show that the varied SERs negligibly influence the time-averaged length of the recirculation zone (about 50 mm off the rear of the strut). However, the low-speed regions in the combustor is increased with SER. High droplet evaporation rates are observable in the downstream of the recirculation zone, and meanwhile continuous evaporation also occurs downstream beyond that due to the local high temperature. The mixing field of the dual-fuel system shows strong inhomogeneity with various compositions of hydrogen/n-heptane/air mixtures in both mixture fraction space and physical space. Moreover, the fraction of heat release rate from hydrogen decreases from 100% to 43.3% due to the increased SERs from 0 to 0.096, and the averaged heat release from hydrogen before blow-off are close, whereas that from n-heptane increases stably. With increased SER, the hydrogen flame base moves upstream towards the strut base, whereas that of n-heptane is lifted off the strut gradually. When SER exceeds some critical value, e.g. 0.096 for the current combustor, the flame blows off, with the two separate reaction zones (upstream hydrogen and downstream n-heptane) fully quenched.