| Summary: | Detonation initiation is a prerequisite to normal operations of an oblique detonation engine (ODE), and initiation-assistant measures are imperative in cases of initiation failure that occur in a length-limited combustor under wide-range flight conditions. This study numerically investigates the initiation characteristics of oblique detonation waves (ODWs) in H<sub>2</sub>-fueled ODE combustors at wide-range flight Mach numbers <i>Ma<sub>f</sub></i> or flight altitudes <i>H<sub>f</sub></i>. Failures of ODW initiation are observed at both low <i>Ma<sub>f</sub></i> and high <i>H<sub>f</sub></i> if no measure is taken to assist initiation. Through analyses of the flow fields and theoretical predictions of the ignition induction length <i>L</i><sub>ind</sub>, the data reveal that the detonation failure at low <i>Ma<sub>f</sub></i> is raised by the significant decrease in the post-shock temperature due to insufficient shock compression, leading to a significant increase in <i>L</i><sub>ind</sub>. The detonation failure at high <i>H<sub>f</sub></i> is caused by the rapid decrease in the combustor inflow pressure as <i>H<sub>f</sub></i> increases, which also results in an increase in <i>L</i><sub>ind</sub>. With further identifications of the key flow structures crucial to detonation initiation, an initiation-assistant concept employing a transverse H<sub>2</sub> jet is proposed. The simulation results show that through an interaction between the incident oblique shock wave and the jet shock wave, the transverse jet helps to initiate an ODW in the combustor at a low <i>Ma<sub>f</sub></i>, and the initiation location is relatively fixed and determined by the jet location. At high <i>H<sub>f</sub></i>, a Mach reflection pattern is formed in the combustor under the effects of the transverse jet, and detonative combustion is achieved by the generated Mach stem and its reflected shock waves. The proposed concept of using transverse jets to assist detonation initiation provides a practical reference for future development of ODEs that are expected to operate under wide-range flight conditions.
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