Exploring the potential of boron carbide in enhancing energy output of solid fuels for SFRJ and hybrid rocket propulsion systems

Boron carbide (B4C) is known for its exceptional hardness and high energy release during combustion, despite its ignition processes presents considerable challenges. This study focuses on exploring the potential of B4C as an enhancer for the energy output of solid fuels designed for hybrid rocket engines (HRE) or solid fuel ramjets (SFRJ). This study presents the successful incorporation of B4C and fluorinated PTFE (polytetrafluoroethylene) polymer into the HTPB (hydroxyl-terminated polybutadiene) fuel matrix, aiming to enhance the ignition, combustion, and regression rate performance of solid fuel. Five different fuel compositions were formulated with varying mass ratios of B4C, and their post-combustion products were characterized using XRD (X-ray diffraction), HRSEM (high-resolution scanning electron microscopy), and EDS (energy-dispersive X-ray spectroscopy) techniques. The HRSEM-EDS analysis confirmed a uniform dispersion of B4C/PTFE additives throughout the HTPB matrix. To evaluate the combustion behavior of the B4C/PTFE additives, an opposite flow burner was employed with a gaseous oxygen oxidizer. The F4 fuel sample, loaded with B4C/PTFE (10/20), exhibited an average regression rate increase ranging from 0.61 to 1.15 mm/s when evaluated within the oxidizer flux range of 36-77 kg/m2s, in comparison to that of pure HTPB (0.4 mm/s to 0.76 mm/s). The ignition delay time was investigated as a key parameter affected by the B4C concentration in the solid fuel formulations. Furthermore, a comprehensive combustion mechanism is proposed and discussed for B4C/PTFE loaded in the HTPB matrix under an oxygen environment. image