To improve combustion performance in a hydrogen-fueled scramjet research engine model for the Mach 8 e ight condition, a thick strut was attached, and the contraction ratio was increased to 8.3. According to results obtained by gas sampling at the exit of the model, a combustion efe ciency of 90% was attained for the fuel e ow rate at A = 0.8. Normal fuel injection into the low-velocity region on the top wall where the recovery temperature was high was found to be effective for ignition. The high pressure in the combustor caused by the thick strut was also found to be effective for combustion. The thrust increase from the no-fuel condition was 420 N for A A = 1.2. The relatively low thrust level was caused by the Rayleigh heating loss and the base drag of the strut. Small amounts of fuel injection upstream of the step changed the combustion condition signie cantly, however, controlled engine operation was dife cult to achieve. Parallel fuel injection resulted in very poor combustion for this engine model. Nomenclature h = step height Pw = wall pressure P1 = nominal static pressure at the exit of the Mach 6.7 nozzle, pressure upstream of the shock train P2 = increased pressure by combustion at the end of the shock train xc = combustion position in the one-dimensional calculation x1 = streamwise distance from the leading edge of the side wall y = vertical distance from the top wall z = spanwise distance from center plane 1F = thrust increase from no-fuel condition ´c = combustion efe ciency A = equivalence ratio of injected hydrogen fuel Alocal = local equivalence ratio