Characteristics of rich flame blowout during the condition transition of a scramjet

The global equivalence ratio (ER1) will change drastically when scramjets carry out the mission of condition transition. The blowout characteristics of partially premixed flame in a fuel-rich condition are investigated experimentally in a cavity-stabilized scramjet combustor. The total pressure, total temperature and Mach number at the combustor entrance are 1.6 MPa, 1486 K and 2.52, which can simulate the flight condition of Mach 5.5 at 25 km altitude. When the final ER1 is relatively small, the range and light intensity of flame increase first and then almost keep constant. The cavity-stabilized flame can be switched from cavity shear layer to jet-wake. Once the final ER1 exceeds a critical value, the rich flame blowout phenomena will appear suddenly. During the blowout process, the flame in the cavity is blown out first and then the flame downstream extinguishes completely along the rear-wall. The intensity of combustion at the flame front is more vigorous with a higher ER1 at the initial combustion state, which is conductive to burn more fuel mixed in the incoming flow. When the initial flowfields are more vigorous, the stabilized flame can be shifted to a stronger combustion state under a higher ER1.