Operating Characteristics of Cylindrical Rotating Detonation Engines Using Liquid Ethanol and Liquid Nitrous Oxide

Rotating detonation engine (RDE) is one of the combustors using detonation waves and is expected to simplify the system and improve thermal efficiency due to their supersonic combustion and compression performance by shock waves. Liquid propellants are commonly used in rocket engines due to their high energy density. However, most of these studies use gas propellants, so it is important to investigate the effect of the combustor length, mixture ratio, and propellant temperature on bipropellant RDE operation. In this study, cylindrical RDEs with liquid ethanol and liquid nitrous oxide were tested under atmospheric pressure conditions. The rotating detonation wave was observed in the cylindrical RDE with the liquid ethanol. About the effect on propagation mode, detonation mode was not observed when the mixture ratio was low, and the range of the mixture ratio in which the detonation mode was observed decreased as the combustor length decreased. When the ethanol liquid temperature was low, the detonation mode was not observed because the atomization performance and combustibility became lower. In addition, the rotating propagation mode was observed when the vapor quality of nitrous oxide was higher than about 9% because the propellant velocity was increased at the higher vapor quality of nitrous oxide, and this improved the atomization. Moreover, the throat pressure was close to the critical pressure for isentropic flow with a smaller ethanol injector diameter. The results of the experimental characteristic exhaust velocity in all combustion tests were in close match with the ideal value for the constant pressure mode. However, when the combustor length was 90 mm, the values in deflagration mode were much lower than the ideal value. Therefore, these results indicated that the combustion region was longer in the deflagration mode and with large ethanol injector diameter than in the detonation mode and small diameter, respectively.