Abstract
A rotating detonation rocket engine (RDRE) with various convergent nozzles and chamber lengths is investigated. Three hundred hot-fire tests are performed using methane and oxygen ranging from equivalence ratio equaling 0.5–2.5 and total propellant flow up to 0.680 kg/s. For the full-length (76.2 mm) chamber study, three nozzles at contraction ratios ϵc = 1.23, 1.62 and 2.40 are tested. Detonation is exhibited for each geometry at equivalent conditions, with only fuel-rich operability slightly increased for the ϵc = 1.62 and 2.40 nozzles. Despite this, counter-propagation, i.e., opposing wave sets, becomes prevalent with increasing constriction. This is accompanied by higher number of waves, lower wave speed Uwv and higher unsteadiness. Therefore, the most constricted nozzle always has the lowest Uwv. In contrast, engine performance increases with constriction, where thrust and specific impulse linearly increase with ϵc for equivalent conditions, with a 27% maximum increase. Additionally, two half-length (38.1 mm) chambers are studied including a straight chamber and ϵc = 2.40 nozzle; these shortened geometries show equal performance to their longer equivalent. Furthermore, the existence of counter-propagation is minimized. Accompanying high-fidelity simulations and injection recovery analyses describe underlying injection physics driving chamber wave dynamics, suggesting the physical throat/injector interaction influences counter-propagation.
Highlights
Rotating detonation engines (RDEs) have recently gained substantial interest as an alternative to traditional deflagration-based propulsion systems, with the theoretical potential to achieve overall engine performance gains
To further understand the flow expansion processes associated with a rotating detonation engine, a detailed study using multiple convergent throat geometries is conducted in the current study
Hot-fire test results for a 76.1 mm diameter modular rotating detonation rocket engine with various convergent nozzle designs are summarized for flow conditions ranging from equivalence ratio φ = 0.5–2.5 and ṁtot = 0.091–0.680 kg/s
Summary
Rotating detonation engines (RDEs) have recently gained substantial interest as an alternative to traditional deflagration-based propulsion systems, with the theoretical potential to achieve overall engine performance gains. For the shortened ec = 2.40 nozzle, detonation mode structure is significantly better ordered compared to the full-length geometry, i.e., the existence of counter-propagating behavior is significantly diminished. This result is consistent with the theory proposed that shock waves reflected back upstream from the annular throat can influence the quality of reactant mixedness, and the detonation mode structure, in the reactant fill region near the injector face. A supporting analysis describing the injector recovery process and accompanying results from high-fidelity simulations of the RDRE are detailed in this manuscript These analyses suggest the interaction between the observed injection response and interaction with a physical throat is one driving mechanism responsible for counter-propagating modal behavior. The results of this work should serve as a basis for further studies to optimize RDRE annular nozzle design, as well as global engine performance
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