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To estimate the enthalpy effects of test gas in a direct-connect dual-mode combustor, an experimental study was conducted. Wall pressures were compared under two cases with different types of air heater (combustion heater and electric heater) at various H2 fuel equivalence ratios. Considering flame holding, dual-mode transition and wall pressure value, matching total enthalpy was found to be more effective than matching total temperature in terms of mitigating vitiation effects in the case of a combustion heater. On the other hand, for vitiation flow, matching total temperature is more effective than matching total enthalpy for ignition to duplicate that of clean air flow. Therefore, flow total condition (total temperature or total enthalpy) should be selected according to experimental candidates.

A quasi-one dimensional calculation was carried out to figure out supersonic combustor performances. Three flow tubes were considered in the combustor region. Those were an air-flow-tube, a combustion-flow-tube and a fuel-flow-tube. A Mach=1 condition was assumed in the combustion-flow-tube. The estimation of a mode-transition was considered as a result of thermal choking. Both clean and vitiated inflows were tested with the calculation model. Experimental combustion tests were also carried out to compare and confirm the validity of calculated results. Mode-transition equivalence ratios and combustor wall pressure distributions were focused to compare between calculated and experimental results. The calculation model estimated the mode-transition equivalence ratio and the thrust performance with the relative errors at about 11% and 6% compared to the experimental results, respectively.

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Supersonic combustion tests were conducted with a direct connected dual-mode combustor. To generate high enthalpy flow, either a hydrogen fueled vitiation heater or a storage heater was used to compare the inflow vitiation effects on the combustor wall pressure distributions. Regarding the storage heated flow, two stagnation temperature conditions were tested. One had a same level stagnation temperature to the vitiated flow, and the other was a higher stagnation temperature which was estimated to gives a matching pressure increase between vitiated and clean air flow. The experimental results showed that the pressure increase ratio of this higher stagnation temperature condition with clean flow seemed to give slightly smaller pressure magnitudes compared to the vitiated flow case at same equivalence ratio. In addition, OH radical gave small effects on pressure distributions. NomenclatureJ/kg H = ramp injector height, H = 6.35mm M = Mach number MW = Molecular weight P = pressure Ru = Universal gas constant T = temperature VAH = Vitiation Air Heater SAH = Storage Air Heater γ = specific heat ratio φ = Fuel equivalence ratio dq = Fuel heat release value, J/kg * = throat condition 0 = stagnation condition air = condition of air flow fuel = condition of fuel flow w = condition on wall