Research on combustion characteristics of the strut-equipped variable geometry scramjet combustor at Mach 2 condition

In this paper, the unstart boundary of the strut-equipped variable geometry combustor was experimentally verified at the Mach 2 condition. Limited by the flow field structure at a low Mach number, the working boundary of the supersonic combustor had certain requirements on the fuel equivalent ratio and combustor expansion ratio. By simulation analyses and static regulations, the optimization of flow field structure and the successful ignition of the strut-equipped supersonic combustor were achieved. To adapt the fuel equivalent ratio with the expansion ratio for performance enhancement, experimental investigations were conducted with Mach 2 condition, where the fuel equivalent ratio ranges from 0.6 to 1.0, and the combustor expansion ratio ranges from 2.0 to 3.43. The conclusions were drawn from qualitative summaries and quantitative analyses. Under the static flow field and a low expansion ratio condition, the starting boundary of the combustor fuel equivalent ratio was restricted to the equivalent ratio interval from 0.6 to 0.8, which can be broadened by the ignition effect. In the process of equivalent ratio upgrading, the high-level heat release intensity required larger expansion ratios for heat exchange, meanwhile, the increased pseudo-shock wave length improved the unstart risk. A stepwise performance enhancement at the 0.8 equivalence ratio was achieved by dynamic regulation, and the flame boundary integration conjecture based on the previous theoretical analyses was proposed for this phenomenon. The performance distribution pattern of the combustor was obtained from the experiments, which showed that the high-performance range is mostly concentrated around the 0.8 equivalence ratio.