Use of a Partially Pre-Mixed Injection Scheme and Pre-Detonator in a Small Scale Rotating Detonation Engine

Abstract

Current interest resides in small scale rotating detonation engines (RDEs) with low mass flows for their potential as small thrusters, robust flame holders, and as a research tool that can be quickly and cheaply modified. Additionally, because the small geometry forces the detonation wave to the limit of detonability, the techniques used to improve stability and operability at the small scale could be used to inform improvements of off design operation in larger RDEs. Recently, a small scale, “Micro-RDE” that operated on nitrous oxide and ethylene at mass flows from 25-75 g/s was developed with an outer diameter of 28 mm and channel gap of 2 mm. Initial testing showed unstable wave modes with a peak frequency of 14.0 kHz were achievable with a Jets in Crossflow (JIC) injection scheme and spark plug initiation. Current efforts looked to improve the detonation wave stability and characterize the subsequent operating envelope and frequencies. To accomplish this, a new partially pre-mixed JIC injection scheme was installed to improve local mixing and a pre-detonation device was used as the ignition mechanism. Results showed successful operation was possible with stable one wave modes occurring over a range of mass flows (0.035-0.068 kg/s) and equivalence ratios (Φ = 0.6-1.4). The single wave mode was observed for the first time in an RDE of this size and operated at frequencies up to 16.6 kHz. Plenum pressure to chamber pressure ratios greater than three were required to achieve reliable detonation. Tests with channel pressure loss due to erosion showed fill height was a mechanism for trends in wave frequency and mode.