The characteristics of a long-time working solid-fuel scramjet combustor have been investigated by experiments and theoretical calculation. Poly-methyl-methacrylate (PMMA) was used as solid fuel and a methane vitiated air heater was designed and built to simulate the flight environment of Mach 6 at a 25 km altitude, where the corresponding inlet total temperature and total pressure was 1600 K and 2.4 MPa. Flow and combustion phenomena were studied by recording combustor pressure and combustion video. The combustion process was analyzed, the fuel regression rate, specific thrust and specific impulse decrease gradually with time, the fuel mass flow rate remains constant. Comparing combustors with cavity or step, the characteristics of self-ignition and self-sustained combustion were studied, which were not consistent with the results from previous works. The results show that with enough inlet total temperature, even with step, selfignition can also succeed, but it cannot maintain stable combustion, until a cavity appeared in combustor.
pmma, experiment, scramjet, self-ignition