Study on Flame Stabilization in a Dual-Mode Combustor Using Optical Measurements

Flame stabilization in a dual-mode scramjet combustor was studied using simultaneous detection of flowfield and reaction zone. The instantaneous reactive flowfield was clearly visualized using an improved pulsed schlieren system, whereas the reaction zone was marked by CH* chemiluminescence. Experiments were performed in a Mach 2.5 model combustor with the total temperature of 1275 +/- 25 K and the total pressure of 1.0 MPa. Ethylene was used as fuel with equivalence ratios varied from 0.258 to 0.411. Four typical flame stabilized locations and corresponding flowfields are presented. When no choke occurs, the flame is stabilized in the cavity or the shear layer. Schlieren images show that the flow in the reaction zone of the latter case is supersonic. When the combustor is choked at the injection location, the flame oscillates between the shear layer and the jet wake, and the flow in the reaction zone becomes subsonic. When the flame is stabilized in the jet wake, autoignition can occur due to the compression of precombustion shock train. The short-lived aerodynamic throat formed near the injection location may be the possible cause for triggering the unsteady flame oscillation. The effects of heat release on flame stabilization modes are discussed.