Mechanism and Control of Combustion-Mode Transition in a Scramjet Engine

Abstract

A sidewall compression scramjet engine operated in two combustion modes under Mach 6 flight condition, weak-and intensive-combustion modes. The weak mode occurred below the overall fuel equivalence ratio (Φ) of around 0.4. Transition from the weak mode to the intensive mode occurred at Φ ~ 0.4, accompanied by a sudden increase in thrust. Mechanisms of the transition were numerically investigated in this study. Our simulations captured the sudden increase in thrust at the mode transition. In the weak mode, combustion occurred in only a region near the topwall where an igniter was installed. The combustion region expanded toward the cowl with boundary-layer separation at the mode transition. Our simulations demonstrated that low ignition capability resulted in the weak mode. We demonstrated that the presence of additional igniters on the sidewalls improved the ignition capability and achieved the intensive mode in the entire Φ range. Nomenclature G H2•O2 = flame index (=

Study on transient process of mode transition in a scramjet combustor with pilot hydrogen

“…Finally, the intensive combustion with boundary layer separation around the fuel injector was attained. This mechanism was confirmed by Kouchi using 3‐dimensional computational simulation. Micka and Driscoll have observed 2 distinct combustion stabilization modes for ramjet operation, namely, the jet‐wake–stabilized and the cavity‐stabilized modes.…”

“…Sullins experimentally achieved the mode transition by increasing the combustor entrance total temperature. Through injecting different fuel flow rates, Takahashi et al and Kouchi et al distinguished 4 combustion modes, namely, blowout, weak combustion, strong combustion, and thermally choked. Turner and Smart investigated combustion modes by using 2 combustion chamber configurations with different lengths of constant area section for flight at Mach 8.…”

Experimental study of mode transition characteristics of a cavity-based scramjet combustor during acceleration

“…Studies have investigated the influencing factors [3][4][5][6] and control methods [7] of dual-mode supersonic combustors. Transition between the scram and ram modes is realized by changing the inflow condition, fuel scheme, and combustor design.…”

“…Zhang et al [16,17] numerically and experimentally analyzed the pressure of ram-to-scram transition under continuously changing inlet flow Mach number. Kouchi and Mitani [7] numerically and experimentally obtained different modes by changing the fuel equivalence ratio under fixed Mach number and found that the mode transition jumps because of changes in the flame stability mode and flame propagation mode.…”