Experimental research on the stability margin of a variable geometry scramjet combustor in wide flight conditions

In this paper, aiming at the situation that when fixed geometry combustors are operating for extended periods under off-design performance characterization conditions, the high thrust cannot be provided during acceleration, a variable geometry scramjet combustor is designed and studied. The experimental study was carried out by the method of interval matching under the combined flight conditions of Mach 2.0/4.0/6.0 and equivalence ratios of 0.6/0.8/1.0/1.2. In this process, the ability of the variable geometry combustor that could continuously regulate the expansion ratio from 1.4 to 3.4 was used for optimum performance. The performance could be effectively optimized by matching the expansion ratio and combustor working conditions. The combustor stability margin δ was used to divide the high-performance region, low-performance region, and instability region under limited working conditions, by which the trend of regulation under the acceleration-cruise process was obtained. Increasing the operating Mach number in the matching intervals of the equivalence ratio to the expansion ratio promoted the movement of the main heat release zone and the increase in the peak pressure ratio. The regulating paths and performance boundary of the variable geometry combustor in a wide flight domain were obtained from a large amount of steady-state/dynamic experimental data.