Investigation of RBCC performance improvements based on a variable geometry ramjet combustor

The use of a variable geometry combustor is one of the most effective methods to improve the performance of a rocket-based combined-cycle (RBCC) engine over a wide range of operating conditions. This paper aims to study the capabilities of a variable geometry combustor operating over a wide range of conditions and determine the performance of the combustor under various inflow conditions. Based on the inflow conditions, the configuration parameters of the combustor were adjusted. Ground direct-connect experiments were conducted under the inflow conditions of Ma 2, Ma 3, Ma 4, and Ma 6, and numerical simulations were performed under the conditions of Ma 3 and Ma 6. The direct-connect experiments showed that the primary rocket operating at a low flow rate can reliably ignite the secondary fuel and maintain a stable and efficient combustion in a variable geometry combustor. Under the inflow conditions of both Ma 4 and Ma 6, smooth transitions of the variable geometry combustor from rocket-ramjet mode to ramjet mode were achieved, and the specific impulses were greatly improved and reached 28.2% and 37.1% of the amplitude, respectively. The numerical simulation showed that the variable geometry combustor can effectively control the combustion heat release region and greatly improve the performance of the combustor. The specific impulse in the combustor increased by 18.6% and 26.2% compared with that in the fixed geometry combustor under Ma 3 and Ma 6 inflow conditions, respectively. It is therefore strongly believed that the variable geometry combustor has significant performance advantages under a wide range of operating conditions.