Numerical investigation of a detonation-assisted fuel injection system in supersonic crossflow

A novel detonation-assisted fuel injection system was developed in this study to achieve highly efficient supersonic combustion in scramjet engines. In this configuration, a Rotating Detonation Combustor (RDC) with an annular shape was coaxially employed around the main fuel injector, where hydrogen was injected perpendicular to the supersonic airflow. The computational domain consisted of a three-dimensional rectangular region, into which a Mach 2.4 supersonic flow was introduced to simulate flight conditions corresponding to Mach 8.0 at an altitude of 30 km. The main fuel injector and the RDC were coaxially connected to the isothermal lower wall of the scramjet engine. In the RDC, a stoichiometric premixed H₂–O₂ mixture was supplied from the bottom to generate a detonation wave. The compressible Navier–Stokes equations were solved under unsteady conditions. As a result, a detonation wave propagated continuously within the RDC, even when connected to the combustor section exposed to the supersonic main stream. The detonation products, accelerated to supersonic speeds, were discharged together with the main fuel into the scramjet combustor. This configuration generated large-scale vortex structures in the main stream, leading to a combustion efficiency up to 1.9 times higher and a 56% reduction in combustor length. This enhancement was primarily attributed to the high-enthalpy detonation products containing reactive radicals, which assisted main fuel penetration, increasing the penetration height by approximately 85%. Furthermore, high-frequency pressure disturbances with helically distributed spatial patterns were observed on the lower wall of the scramjet combustor, which were considered to contribute to combustion enhancement. These results demonstrate the effectiveness of detonation-assisted injection and highlight its potential as a solution to the long-standing challenges of stable and efficient combustion in supersonic propulsion systems.