Combustion characteristics of strut-injection supersonic combustor with local oxygen enrichment

To extend the operational envelope of scramjet engines to high-altitude flight conditions, local oxygen enrichment has emerged as a promising strategy to enhance combustion performance. This study conducts a high-fidelity numerical investigation into the combustion characteristics of a strut-injection supersonic combustor with local oxidizer enrichment using large eddy simulation. The research focuses on elucidating the complex flow-field structures, flame stabilization mechanisms, and turbulence–chemistry interactions under varying oxygen enrichment levels. Furthermore, the performance of hydrogen peroxide as an alternative oxidizing agent is evaluated and compared against pure oxygen injection. The results indicate that local O2 enrichment significantly improves flame anchoring and overall combustion efficiency, with the global efficiency at the combustor exit reaching 95%, an approximate 15% increase compared to the baseline case. This promotes a transition from a mixed premixed/diffusion combustion mode to a mixing-controlled flamelet regime, which accounts for up to 77.75% of the combustion process under optimal enrichment, as chemical reactions are no longer the rate-limiting process. Notably, the study finds that H2O2 injection is substantially more effective than O2 injection under an equivalent oxygen mass flow content, boosting the flamelet regime contribution from 60.43% to 75.95%. Computational singular perturbation and tangential stretching rate analyses show that the decomposition of H2O2 creates a unique radical farming zone behind the strut, establishing a more stable and intense reaction core that actively promotes combustion downstream. These findings provide fundamental insight into the physico-chemical mechanisms of oxygen enrichment and offer valuable theoretical guidance for the design of advanced high-performance scramjet engines.