Abstract
The ignition and blowout characteristics have a significant impact on the performance and operating limit of the scramjet. In this study, direct-connected ground tests of a typical scramjet combustor have been conducted to simulate the high-altitude flight condition of Mach 6. The incoming air has a total temperature of 1689 K and a dynamic pressure of 30 kPa. The ignition and blowout characteristics of the dual strut/cavity combined flame stabilizers in the scramjet are obtained. The immediate response of pressure at key positions is used to analyze the forward propagation characteristics of pressure during the ignition process and the pressure variation during the flame blowout process. The flame distribution and temperature variation during the ignition and blowout processes are obtained by high-speed photography, OH⁎ spontaneous radiation photography, spectrometer and multispectral imaging equipment. Results indicate that the process from local ignition to global ignition successfully has durations lasting for hundreds of milliseconds, comprising four stages with two pressure lift stages. The flame diffusing forward and upstream cavity igniting successfully are the main processes, constituting 60% and 30% of the duration, respectively. During the ignition process, the pressure response time of the two-stage cavity differs by several milliseconds. And the flame is transmitted forward to the upstream cavity through combustor walls. As the ignition process progresses under high equivalent ratio (ER) conditions, flame stabilization mode shifts from stabilizing flame in the recirculation zone of the cavity to stabilizing flame in the shear layer of the strut. Upon completion of global ignition, the flame temperature at the shear layer of the cavity upstream exceeds 2700 K, but decreases to 2125 K as the core reaction zone is shifted from the top of the strut to the tail and bottom of the cavity when the ER decreases. Two pressure drops occur during the flame blowout process, and the critical ER of the global blowout is approximately 0.33. The primary shear layer flame is blown out during the first pressure drop, and the intensity of the cavity flame decreases. Finally, the second pressure drop occurs as the flame in the cavity moves downstream and extinguishes.
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