Role of Ignition Delay in Rotating Detonation Engine Performance and Operability

Rotating detonation engines (RDEs) represent a promising technology for improving the performance of existing aerospace combustors, but additional research is needed to characterize the operability limits and performance of these devices. In particular, contact surface burning and preignition of propellants can have a profound impact on both performance and limit-cycle detonation behavior, but the detailed mechanisms behind this behavior and the associated scaling with chamber pressure are not well understood. To this end, ignition delay times are computed using a constant pressure-enthalpy, homogeneous reactor model and compared with typical RDE cycle times and operating conditions. Results are presented for combustion in both oxygen and air at various pressures using hydrogen, methane, and natural gas fuels. Results suggest that preignition of propellants before wave arrival may dominate chamber behavior and prevent stable limit-cycle detonation from occurring with certain propellant combinations above certain pressures. The impact of liquid injection is also considered with respect to changes in mixed gas temperature and vaporization delay. Finally, a simplified assessment of the injector dynamic response and turbulent mixing environments are considered in an effort to demonstrate the significance of ignition delay relative to these other mechanisms. These results support observed high-pressure RDE operating behavior in tests conducted at Purdue University, and they provide insight into potential operability limits and scaling of RDEs to high operating pressures.