Experimental Investigation of H2-Air Mixtures in a Rotating Detonation Combustor

Abstract

The operating range and wave speed performance of a Rotating Detonation Combustor (RDC) is characterized for hydrogen-air mixtures for three fuel injection schemes and two air injection schemes. The fuel injection scheme is altered by changing the total number of injection orifices and the individual orifice area, while maintaining the same fuel mass flux across the three schemes. The operability, performance and combustion-induced pressure rise due to the addition of a back-pressurizing convergent nozzle is also characterized. While the operating range is largely unaffected by changes in the length-to-diameter ratio of the fuel injector orifices, higher length-to-diameter ratios correspond to a lower number of pop-out events. Pop-out event is defined as a transitional RDC operation where there is a sudden abatement of the continuously propagating detonation wave, once established inside the combustor. Increased air injection area diminishes the operability, while producing high stochasticity in the performance of the RDC. The length-to-diameter ratio of the fuel orifices has a significant impact on the number of detonation waves that can exist in the chamber. For the highest length-to-diameter ratio of the fuel orifices, and at the highest air flow rates, the RDC supports multiple detonation waves inside the chamber. Without the convergent nozzle attachment, 80% of Chapman-Jouguet (C-J) detonation speed is achieved for all three fuel injection schemes. C-J detonation wave speed is achieved in the annulus when the RDC is back-pressurized using the nozzle. The ratio of reactant fill-height to the detonation cell-width tapers at the lean and rich operating conditions, while peaking at an equivalence ratio of around 1.2. The detonation-induced static pressure rise produced in the RDC is found to be dependent on the air flow rate and the equivalence ratio of the reactants.