Effects of Ti and Mg particles on combustion characteristics of boron–HTPB-based solid fuels for hybrid gas generator in ducted rocket applications

Abstract

In the field of propellants and explosives, boron has been considered as an attractive fuel due to its calibre to produce high energy density. Therefore, boron as a fuel has great prospect for application in solid fuel ducted rocket (SFDR) with hydroxyl-terminated polybutadiene (HTPB) which is widely used solid fuel. Experimentally, it has been observed that ignition and combustion of boron is problematic due to boron oxide (B2O3) coating around active boron which inhibits its ignition/combustion. In the present study, titanium and magnesium have been used with boron-HTPB based solid fuel as burning promoters. Various combustion parameters have been evaluated for nine different fuel compositions. An opposed flow burner (OFB) system has been used for fuel evaluation with the help of gaseous oxygen (GOX) impingement where oxygen mass flux (Gox) is maintained between 20 and 57 kg/m2-s. Favorable result has been observed for boron-magnesium combinations as compared to boron-titanium. Around 18% enhancement in regression rate has been achieved for boron-magnesium-HTPB sample (at max. Mg %) compared to that of boron-HTPB sample. In all the boron-based samples, greenish appearance has been observed during combustion which corresponds to BO2 emission. Spectroscopy analysis confirmed the same. Burning events have been analysed using color and high-speed camera. Condensed combustion products (ejected from the burning surface) have been analysed by various material characterization techniques such as: FE-SEM, EDX, XRD, and TGA. Through TGA, the active residual boron content in the condensed product of magnesium-based sample is found to be 33%. This value is found to be the lowest among the tested fuel compositions. The present investigation has been mainly focused on the formulation of new composition of boron-based solid fuel having high energy density.