Regenerative cooling technology provides thermal protection for the combustion chamber of scramjet engines through active heat exchange. However, the kerosene, after absorbing high-temperature heat, transits from a liquid to a supercritical state, yielding a physicochemical properties. This transition leads to substantial variations in supersonic combustion processes involving supercritical kerosene injection. This paper systematically reviews research progress on the physicochemical properties of supercritical kerosene and its injection-mixing-combustion processes. First, it introduces the application of supercritical kerosene in scramjets and current challenges. To address these issues, the study analyzes the physicochemical characteristics of China’s domestic RP-3 kerosene under near/supercritical conditions within regenerative cooling channels and nozzles at different temperatures. It further compares the advantages and limitations of methods such as experimental measurements, component surrogate models, modified equations of state, and machine learning for obtaining kerosene thermophysical property parameters. Subsequently, the paper reviews advancements in supercritical kerosene injection and mixing processes under various environmental conditions. Notably, existing studies primarily focus on mixing mechanisms in static environments, coaxial injection configurations, and transverse jet mixing under low-speed crossflow conditions, while research on high-speed crossflow conditions remains limited. Additionally, the impact of mixing enhancement schemes on supercritical kerosene injection-mixing processes has not been explored. Finally, the study summarizes key findings regarding supercritical kerosene combustion characteristics, proposes optimizing injection parameters to mitigate combustion oscillations induced by phase transitions, and suggests future research directions to establish coupled mixing/combustion models applicable across a wide range of velocities.

A numerical and experimental study was conducted to investigate the Laser Ablation (LA) ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder. The experiments were operated under a Mach number 2.92 supersonic inflow, with stagnation pressure of 2.4 MPa and stagnation temperature of 1600 K. Reynolds-averaged Navier-Stokes simulations were conducted to characterize the mixing process and flow field structure. This study identified four distinct LA ignition modes. Under the specified condition, laser ablation in zero and negative defocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition (LADI) mode and Laser Ablation Re-Ignition (LARI) mode, correspondingly. LA ignition in a local small cavity, created by depressing the flow field regulator, could facilitate the ignition mode transforming from LARI mode to Laser Ablation Transition Ignition (LATI) mode. On the other hand, the elevation of the flow field regulator effectively inhibited the forward propagation of the initial flame kernel and reduced the dissipation of LA plasma, further enhancing the LADI mode. Based on these characteristics, the LADI mode was subdivided into strong (LADI-S) and weak (LADI-W) modes. Facilitating the transition of ignition modes through alterations in the local flow field could contribute to attaining a more effective and stable LA ignition.

The increasing demand for future hypersonic vehicle maneuvers heightens the importance of the wide speed range scramjet technology development. However, the wide-range inflow conditions will cause significant changes in the flow, mixing, and combustion processes. In particular, supersonic combustion is a typical diffusion flame dominated by the mixing process, and changes in the inflow conditions have a considerable impact on the fuel transport and mixing process, which can lead to a series of unsteady combustion phenomena. This paper reviews and analyzes the flow and combustion process of the wide speed range scramjet. Firstly, the basic working process and applications of scramjets are briefly introduced. Then the key problems in and research on the supersonic flow and combustion process with the low Mach number inflow, high Mach number inflow and wide speed range inflow at home and abroad are discussed, followed finally by a summary and suggestions for follow-up research.

The atomization process of a liquid jet in a divergent cavity-based combustor was investigated experimentally using high-speed photography and schlieren techniques under a Mach number 2.0 supersonic crossflow. Gas-liquid flow field was studied at different divergent angles and injection schemes. It is found that complex wave structures exist in the divergent cavity-based combustor. The spray field can be divided into three distinct zones: surface wave-dominated breakup zone, rapid atomization zone and cavity mixing zone. A dimensionless spray factor is defined to describe the concentration of spray inside the cavity qualitatively. As a result, it is revealed that for the large divergent angle cavity, the injection scheme near the upstream inlet has a higher penetration depth but a lower spray distribution, where the injection scheme near the cavity has a more spray distribution. For the small divergent angle cavity, the injection scheme near the upstream inlet also has a higher penetration depth and the injection scheme near the start point of the divergent section has a more sufficient spray distribution. The small divergent angle cavity-based combustor with the upstream wall transverse injection is an optimized injection scheme to improve both penetration and spray distribution inside the cavity. Finally, a penetration depth formula is proposed to explain the spray and distribution behaviors in the divergent cavity-based combustor.