Unraveling the role of dual Ti/Mg metals on the ignition and combustion behavior of HTPB-boron-based fuel

Abstract

Metal additives play an essential role in explosive and propellant formulations. Boron (B) is widely used in propellant applications owing to its high energetic content. The addition of B to explosives and propellants increases their energy density, making them more efficient and powerful. Nevertheless, B forms oxide layers on its surface during combustion, slowing down the combustion rate and reducing rocket motor efficiency. To overcome this issue, other metal additives such as aluminum (Al), magnesium (Mg), and titanium (Ti) are revealed to be effective in boosting the combustion rate of propellants. These additives may improve the combustion rate and therefore enhance the rocket motor’s performance. The present study focused on preparing and investigating the ignition and combustion behavior of pure hydroxyl-terminated polybutadiene (HTPB)-B fuel supplemented with nano-titanium and nano-magnesium. The burn rates of HTPB-B fuel samples were evaluated on the opposed flow burner (OFB) under a gaseous oxygen oxidizer, for which the mass flux ranges from 22 kg/(m2·s) to 86 kg/(m2·s). The addition of Ti and Mg exhibited higher regression rates, which were attributed to the improved oxidation reaction of B due to the synergetic metal combustion effect. The possible combustion/oxidation reaction mechanism of B–Mg and B–Ti by heating the fuel samples at 900 °C and 1100 °C was also examined in a Nabertherm burnout furnace under an oxygen atmosphere. The post-combustion products were collected and further subjected to X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analyses to inspect the combustion behavior of B–Ti and B–Mg. It has been observed that the B oxide layer at the interface between B–Ti (B–Mg) is removed at lower temperatures, hence facilitating oxygen transfer from the surroundings to the core B. Additionally, Ti and Mg decreased the ignition delay time of B, which improved its combustion performance.