Mixing and heat-release modulation of liquid kerosene by high-enthalpy jets in RBCC at Mach 3

At low Mach numbers, the low total temperature of airflow reduces the evaporation of liquid kerosene and limits chemical reactions. Thus, reliable ignition and stable combustion are challenging for RBCC. High-enthalpy jets are often used as pilot flames to assist ignition and stabilize flames. In this paper, ground direct-connect experiment and numerical methods were used to investigate the influence mechanism of high-enthalpy jets on the mixing and heat release characteristics of liquid kerosene in RBCC at Mach 3. The results show that the injection equivalence ratio ( ER ), rocket flow rate ( Q ), and rocket oxygen-to-fuel ratio ( O/F ) significantly affect the mixing and heat release processes. The development of the fuel-air mixing layer exhibits typical nonlinear characteristics. The growth process can be categorized into four distinct stages. The enhancement of the mixing by high-enthalpy jets is primarily attributable to the synergy of baroclinic vorticity and stretching vorticity, with dilatational vorticity exhibiting a non-essential role. The findings indicate that the three factors exert distinct effects on the flame stability zone, and the combustor exhibits a state of multifaceted combustion modes coexistence. However, a notable disparity exists in the contribution of these combustion modes to heat release. Lean premixed combustion emerges as the predominant mode, accounting for over 50 %, while diffusion combustion contributes the least, not exceeding 15 %. Additionally, the heat release proportion of rich premixed combustion is moderately higher than that of diffusion combustion. The coupling effect analysis of ER - Q, ER - O/F , and Q - O/F clarified the parameter-performance relationship. Within the range ( ER =0.3–0.4, Q = 0.2–0.25 kg/s, O/F = 1.4–1.6), both high combustion efficiency and mixing efficiency can be maintained simultaneously.