Powder ramjets are a kind of vehicle propulsion system with high specific impulse and efficiency. They provide significant benefits in terms of extended propulsion and thrust adjustment. The pursuit of a highly reactive fuel appropriate for powder ramjets is likely to stimulate advancements in innovative propulsion systems, which are crucial for deep space exploration and long-term space missions. This work presents experimental studies on the thermal oxidation and laser ignition performance of aluminum–magnesium–lithium powders at atmospheric pressure. TG-DSC curves of powders in three heating rates were obtained. The ignition processes and ignition delay times were recorded by a CO₂ laser ignition experiment system at a laser power of 10~60 W. The results show that at a lower heating rate of 10 K/min, the powder’s thermal hysteresis is less, and the powder energy released in stage I is more concentrated. However, the degree of heat release concentration approached a similar level at heating rates of 30 K and 50 K. The ignition delay time decreased as the laser flux density increased. When the laser flux density exceeds 80 W/cm², the effect of laser power on the ignition delay time decreases. At atmospheric pressure, the mathematical relationship between ignition delay time and laser flux density is given. Finally, the powder ignition processes at different laser powers are represented graphically.

In solid propellants, the combustion of aluminum particles often occurs in a hydrocarbon combustion atmosphere. In order to study the combustion energy release process of aluminum particles during propellant combustion, we carried out a study of the combustion behavior of aluminum particles in the combustion atmosphere of hydrocarbon fuels and conducted experiments using a plane flame burner to observe the combustion process of aluminum particles in a methane plane flame combustion atmosphere. High-speed microscopy revealed a new special combustion phenomenon: ejection combustion with the release of internal components from a point on the particle at high speed, in addition to the already observed particle microexplosions. Both phenomena show faster-than-normal combustion with short combustion energy release times. The experiments also showed that the combustion behavior of aluminum particles changes with the combustion environment. As the ambient effective oxidizer mole fraction increases from 13% to 29%, the basic combustion behavior of aluminum particles changes from vapor evaporation combustion to multiphase surface combustion. In addition, the percentage of aluminum particles burned by ejection increases from 18.2% to 49.2%, which becomes the dominant mechanism in the special combustion phenomenon of aluminum particles. This paper argues that the multiphase surface combustion provides higher heating rates due to the heat production collected on the particles and the diffusion combustion in the air around the aluminum particles, compared with the evaporation combustion. Therefore, the rate of temperature rise within the particle is affected by the ambient oxidant concentration, leading to a transformation from microexplosion to ejection combustion. The effect of the temperature of the combustion environment on this phenomenon has also been investigated through experiments conducted under different conditions.

Powder-fueled ramjets show great potential due to their unique advantages. How to further improve ramjet performance through methods such as fuel improvement is also an important focus. In this paper, a 14 km, Ma 3.0, ground test of a powder-fueled ramjet using boron–aluminum composite powder fuel (B–Al composite powder fuel) was conducted. The feasibility and combustion performance of B–Al composite powder fuel were verified. Under the condition of an air–fuel ratio of 19.39, the ramjet achieved independent self-sustaining combustion for 10 s, and the characteristic exhaust velocity efficiency (${\eta }_c^{*}$) reached 81.84%. Through SEM-EDS, XRD, and XPS, this study systematically analyzed the surface morphology, composition, and chemical state of the wall deposits in the combustion chamber after the test. The combustion behavior of the B–Al composite powder fuel in the ramjet was clarified. The composite powder fuel could be converted into smaller and more combustion-favorable reaction basic units during the combustion process. However, the imbalance and unevenness of Al and B in the combustion reaction and the non-reaction or reaction termination of B particles remain significant issues. This study shows that B–Al composite powder fuel has a good application basis and potential, and provides experimental data support for the subsequent improvement and optimization of the B–Al composite powder fuel system.

With the development of energy storage and conversion or advanced propulsion systems, heat transfer enhancement methods have become widely applied

The development of powder-fueled ramjets is challenged by the mechanisms of flow mixing for the combustion of powder fuel in supersonic airflows. This paper describes a series of numerical simulations on the injection process of boron powder fuel in a cavity-based supersonic combustion chamber with induced shock. Under different solid-to-gas ratios ranging from 20 to 0.1, this study explored the evolution of supersonic flow fields with strong shear and discontinuities. It also discusses the flow processes and mixing characteristics of powder fuel within them. The study found that the enhancement of powder fuel mixing is mainly related to the rotational regions of large-scale vortex structures. Vortex structures with the required intensity and area can be obtained by adjusting the appropriate solid-to-gas ratio. Moreover, reasonable induction methods can enhance the interaction between particles and vortex structures, thereby achieving mixing enhancement. The interaction between powder fuels and the peripheral rotating regions of these vortices significantly improves the mixing efficiency, with the highest average mixing efficiency increased by 30%. This research lays a foundation for developing mixing enhancement strategies and supports the advancement of efficient and stable powder-fueled ramjets.