Precise prediction of aerothermal loads is significantly limited by the unclear interactions between the thermal protection system surface and the surrounding high-enthalpy gas. To address this, we propose an optical diagnostic method based on optical emission spectroscopy and laser absorption spectroscopy to investigate the gas–surface interactions within the boundary layer. Experiments are conducted in an air plasma flow produced by the 1.2 MW inductively coupled plasma wind tunnel at the China Academy of Aerospace Aerodynamics with an enthalpy of 20 MJ/kg and a heating time of 100 s. The cylindrical samples made of pure silicon carbide are tested, and quartz samples with the same exposed geometry are tested in parallel as a reference material. The optical emission spectroscopy system has four spectrometers to cover the wide wavelength range of 200–1100 nm, providing qualitative, spatially, and spectrally resolved measurements of the multi-species radiative emission adjacent to the sample surface. Laser absorption spectroscopy is deployed at different axial locations to quantify the number density and translational temperature of OI (3s5S) with a 500 Hz scanning rate and 200 kHz acquisition rate. Additionally, the surface temperature of each sample is detected by an infrared pyrometer. Scanning electron microscopy and energy dispersive spectrometry are performed before and after the plasma heating. Our measurement results provide valuable information on surface reaction pathways and catalytic recombination effects on atomic oxygen number density distributions. Finally, these self-consistent results show that the proposed method is reliable to deeply investigate gas–surface interactions within boundary layer in harsh aerothermal environment.

The mechanical and combustion properties of metal-nested composite hybrid rocket fuel grains composed of spiral aluminium (Al) frameworks fabricated using three-dimensional (3D) printing with an embedded paraffin-based fuel were investigated. The mechanical properties of the resulting grains were evaluated by compression tests. In addition, the combustion characteristics of the Al composite grains were examined in a lab-scale hybrid rocket engine with gaseous oxygen as the oxidizer at an initial mass flow rate of 17.9 g/s. Pure paraffin-based (PP) and acrylonitrile–butadiene-styrene (ABS) composite grains were also tested as baseline fuels for comparison. The Al-A composite grain exhibited superior mechanical and combustion properties, with Young modulus, yield stress, and regression rate increased by 757.1%, 381.3% and 52.5% compared with the PP grain. The Young modulus and combustion efficiency were also further improved, by 51.0% and 14.9%, respectively, by including perforations in the spiral blades. These improvements are discussed in detail herein based on experimental data together with numerical simulations. Emission spectra of the engine plumes were also acquired and used to qualitatively analyze the combustion characteristics of the Al blades.