Ignition and Combustion Characteristics of Boron-Enriched Hypergolic Solid Fuels with High-Concentration Hydrogen Peroxide

Boron-loaded solid fuels have emerged as promising candidates for hybrid gas generator-based ducted rocket (HGDR) propulsion systems due to their exceptionally high volumetric energy density. The decoupled fuel-oxidizer architecture of the HGDR concept, in turn, enables thrust modulation and improved mission flexibility, motivating the development of rapidly igniting, energy-dense boron fuels. These advantages make them highly suitable for next-generation aerospace propulsion technologies. In this study, the hypergolic ignition and combustion characteristics of boron-loaded paraffin-based solid fuels were experimentally investigated using high-concentration hydrogen peroxide as the oxidizer, with a focus on their potential for ducted rocket applications. Fuel samples were prepared with boron concentrations of 10%, 20%, and 30% by weight, and their performance was evaluated using a series of diagnostic techniques, including ignition delay time (IDT) measurements via drop tests, Gas-phase Temperature profiling, BO2 chemiluminescence imaging, and UV-visible spectroscopy. The results reveal that the increase in boron content substantially enhances combustion performance. The IDT decreased progressively from 1.93 ms for pure paraffin (PW) to 1.47, 1.01, and 0.78 ms for 10%, 20%, and 30% boron loading, respectively, accompanied by an increase in the peak combustion gas temperature to 949°C for PWB30. Optical diagnostics confirmed a substantial rise in BO2 emission intensity with higher boron loading; for the 30% boron-loaded case, all major BO2 peaks were prominently observed, indicating greater boron participation in the gas-phase reaction and higher overall energy release. Thermogravimetric analysis of the collected condensed combustion products showed a substantial active-boron content in the residues at 20% and 30% loading (33% and 23%) compared with 1.4% at 10% loading, indicating that a fraction of boron survives combustion at higher loadings even as energetic output increases. These findings provide key insights for optimizing boron-based hybrid fuels and demonstrate their capability to produce quick and energy-rich hypergolic ignition.