Design and Performance Evaluation of Plug Nozzle for Rotating Detonation Wave Engine

In a rotating detonation wave engine (RDE), a unidirectional detonation wave could be created and the exhaust gases are expanded through an annular plug nozzle producing thrust. Empirical relations reported in open literature based on detonation cell size are used to design the combustor. Hydrogen is chosen as the fuel, while air is selected as the oxidizer. The RDE hardware has been realized, and the test facility is being modified at National Combustion Centre for Research and Development (NCCRD), IIT Madras, to carry out static tests. In order to obtain necessary increment in thrust for propulsion applications, a plug nozzle is designed based on simple wave theory under stoichiometric condition. The inlet conditions to the nozzle are established based on “axial flow model” of RDE reported in open literature. As the hydrogen and air are entering as two different streams perpendicular to each other, a simple mixing analysis is carried out to evaluate the mixture properties ahead of the detonation wave. The Chapman Jouguet (CJ) detonation computations are carried out using the shock and detonation toolbox runs in conjunction with Cantera software assuming chemical equilibrium. The modelling of the flow field downstream of the detonation wave is established using the solution of integral mass, momentum and energy equations written for the streamline flow from detonation wave to the exit of the combustor. These conditions are used to evaluate the propulsion parameters at different fuel-based equivalence ratios (0.7–1.3) as a result of expansion through the plug nozzle. The increment in fuel-based specific impulse resulted from the present analysis for our configuration using H₂–air is 18% due to the presence of plug nozzle for the stoichiometric composition at a nozzle entry stagnation pressure of 6.9 bar. The fuel-based specific impulse based on the “axial flow model” reported in the literature for the stoichiometric hydrogen–air mixture at the combustor exit static pressure of 1 bar without plug nozzle is 5383 s. For the present combustor at the same condition, it is 5474 s, which appears to be close while modelling the complex processes using simplified model equations. Several input conditions and combustor–plug nozzle combined performance parameters would be utilized for setting the conditions for the experiments.