Study on heat release characteristics of the dual composite flame stabilizers for the dual-mode scramjet

The paper studies the heat release (HR) characteristics of a dual-mode scramjet equipped with the dual composite flame stabilizers under simulated free-stream conditions of Mach 6 and dynamic pressure of 30 kPa, through ground direct-connected tests and OpenFOAM numerical simulation. This study focuses on the three-dimensional distribution of subsonic/supersonic HR, local combustion modes, and the variations in HR during the ram-scram mode transition. The results indicate that the high-enthalpy jet transports the high-temperature and fuel-rich gas in the cavity to the mainstream through the ejection effect of the supersonic flow, causing the heat release zone to move to the mainstream. So that the mainstream subsonic-diffusion combustion zone is expanded and is evenly distributed, and then the HR trailing zone downstream of the thermal throat is shortened. The study highlights the different matching characteristics between subsonic flow and HR formed by the dual composite flame stabilizers under high and low equivalence ratio (ER). Optimized injection schemes need to be selected to obtain higher combustion efficiency at different equivalence ratios. In the region of the first-stage composite flame stabilizer, a distinct phenomenon of subsonic/supersonic mixed HR is observed. Subsonic HR predominates under the ramjet mode, while the subsonic HR tends to equal supersonic HR under the scramjet mode. Upstream of the thermal throat, subsonic HR exceeds 80 %, and supersonic heat release has a tendency to gradually decrease. Furthermore, when the ER of two-stage dispersed injection is <0.5, the heating amount per kilogram of air is <1.06 MJ, and the thermal throat cannot be formed, causing the ram-scram mode transition to occur. Conversely, for single-stage concentrated injection, the boundary of ER and heating amount decreases. The study provides support for the design of injection schemes and the regulation of mode transition for dual-mode scramjet based on the HR performance.