Advances in Steady-State Operation of an Air-Cooled Rotating Detonation Engine

This study investigates the steady-state performance and detonative behavior of an air-cooled hydrogen–air rotating detonation combustor (RDC) developed for future gas-turbine integration. The combustor employs a backside-cooled, thermal-barrier-coated annular liner and was evaluated in two configurations: a short transition duct, used to test the RDC in isolation and confirm detonative operation through aft-end imaging, and a transition duct designed to mix the combustion products and the cooling air and to condition the flow upstream of the turbine inlet. High-frequency pressure measurements, OH* chemiluminescence measurements, thermocouples, and aft-end imaging characterized the detonation structure, mixed-flow properties, and hardware thermal loading. Detonative operation was confirmed in both configurations: in the short transition-duct setup, coherent detonations occurred at primary equivalence ratios near stoichiometric and above, while leaner mixtures produced weaker, incoherent modes. In the turbine-representative transition duct, detonative operation was initially limited to conditions near a primary equivalence ratio of 1.20 at a dilution ratio of 5.2, but reducing the dilution level expanded the detonative envelope toward stoichiometric operation. Across all conditions, the RDC required approximately 15 seconds to reach thermal steady state, displaying an axial rise in wall temperature. A 110-second test demonstrated system endurance and transition duct thermal steady state, during which combustion efficiency progressively increased and stabilized near 99%, while pressure losses decreased. The transition duct further moderated downstream unsteadiness, reducing pressure-fluctuation amplitudes by up to a factor of 2.1 and producing uniform exit profiles, with total pressure varying by ~5% and total temperature by less than 10% across 20–80% span. These results identify favorable operating regimes and advance understanding of the long-duration operability of air-cooled RDCs.