A modified sidewall-compression-type scramjet engine was tested under M8 flight condition. A strut with a long tail led to a 60% higher maximum thrust increment than a strut with a truncated tail, while allowable fuel flow rate (i.e., the flow rate at engine unstart limit) was almost identical. To increase the allowable fuel flow rate and the maximum thrust increment due to combustion without engine unstart, distributed injection in vertical direction and installation of ramps in the isolator between the inlet and the combustor were applied. Distributed fuel injection led to a 30% higher maximum thrust increment than the uniform fuel injection, and the installation of the ramps also gave a 30% higher one than that in the engine without ramp. Gas-sampling at the exit of the engine with distributed fuel injection showed 88% of bulk combustion efficiency. Specific impulses of the maximum thrust increments, δIsp , of the modified engine were 60–80% higher than that of the original engine.
