Combustion of HTPB-based solid fuels containing Viton-coated Boron for hybrid rocket applications

The performance of hybrid rocket propulsion systems can be significantly enhanced by incorporating metal additives in solid fuels. This study investigates the ignition, combustion, and regression rate of hydroxyl‑terminated polybutadiene (HTPB)-based solid fuels supplemented with Boron (B) and Viton. The investigated fuel compositions comprise pure HTPB, HTPB with 10 wt.% and 15 wt.% B (designated H-B10 and H-B15), and HTPB containing B@Viton composites with 10 wt.% and 15 wt.% B@Viton (denoted as H-B10V10 and H-B15V10). Ignition and combustion experiments were conducted using a counterflow burner to assess the influence of B@Viton additives on HTPB-based solid fuels under varying oxygen mass flux conditions. To understand the thermal decomposition and oxidation behavior of B@Viton additives, thermogravimetric-differential scanning calorimetry (TG-DSC) was conducted, followed by an analysis of their oxidation behavior within the HTPB matrix. Results revealed that the addition of Viton altered the oxidation kinetics of B, leading to faster decomposition and gasification. Incorporating 10 wt.% B@Viton in HTPB (H-B10V10) resulted in a 52% regression rate increase compared to pure HTPB at an oxidizer mass flux of 74 kg/(m²·s). Pure HTPB had the shortest ignition delay time with 227 ms, the ignition delay time increases with an increase in the weight percentage of B, except for Viton-coated samples H-B10V10 (232 ms) and H-B15V10 (241 ms). A proposed combustion mechanism suggested that Viton enhances B combustion by facilitating oxide layer removal and promoting gas-phase reactions.