Combustion Characteristics of Ramjet Fuel Grains with Boron and Aluminum Additives

An experimental investigation of the effect of boron (B) and aluminum (Al) additives to fuel-rich propellant for a solid fuel ramjet application was performed. In this research, depending on the composition of metal particles, three types of fuel grains with 15 wt % ammonium perchlorate particles were prepared and tested. To provide a short ignition delay, an ignition support material consisting of $\mathrm{NC}/{\mathrm{BKNO}}_3$ and a composite propellant were coated on the fuel grain. For the test, an oxidant gas having a controlled temperature and pressure and an oxygen composition close to that of the air in a ramjet combustor was supplied using an ethanol-blended hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) gas generator. Air simulant gas was supplied with an average mass flow rate near $150\mathrm{g}/\mathrm{s}$ and a Mach number of 0.21 in the fuel grain port. Through the test, the noticeable effect of B particles on combustion was confirmed by a high regression rate over $0.5\mathrm{mm}/\mathrm{s}$ and combustion efficiency over 80%. Al particles were not effective additives individually; however, Al particles contributed to the ignition of B. In addition, metal oxide particle deposits on the nozzle confirmed the existence of a two-phase flow.