Experimental and numerical investigation of a methane-fueled variable geometry RBCC combustor

Variable-geometry combustors play a key role in enabling high-performance operation and mode transitions in RBCC engines. In this study, the combustion characteristics of methane in an RBCC combustor are investigated by ground direct-connect experiments. Three methane reaction mechanisms are further assessed through numerical simulations and validated against the experimental data to evaluate their predictive accuracy. The best-performing mechanism is then adopted to analyze the effects of throat height on the coupled flow and combustion behavior. The main conclusions are as follows: (1) The methane-fueled RBCC combustor can achieve auto-ignition and maintain stable combustion, with the maximum combustor pressure reaching 0.27 MPa. As the equivalence ratio increases, the pressures in both the combustor and the isolator rise, and the shock train becomes stronger and moves further upstream. (2) The results obtained with the three methane reaction mechanisms are generally consistent with the experimental data and can reasonably capture the pressure-variation trends in the combustor. However, discrepancies remain in predicting the exact shock-train location. Comparative analysis shows that the 7-step mechanism provides the closest agreement with the experimental pressure distribution, with shock-train position errors within 10% and an overall deviation within 7%. Overall, the 7-step mechanism accurately captures the key features of the supersonic combustion flow and exhibits good potential for engineering applications. (3) The engine performance is strongly influenced by the geometric configuration of the throat. As the throat height decreases, the combustor pressure increases, and the shock train moves further upstream with higher intensity. At the same time, reducing the throat height leads to a decrease in heat release and combustion efficiency. In particular, reducing the throat height from 2.64 H to 2.36 H results in a 34% reduction in heat release and an 8.5% decrease in combustion efficiency.