Analysis of solid propellant combustion behavior under electrothermal plasma injection for ETC launchers

Enhanced burn rates of solid propellants through plasma erosion has been studied showing evidence of increased burn rate with injection of electrothermal plasmas into the propellant. These experiments are designed to evaluate the effectiveness of maximizing energy versus momentum transport, and the influence of geometry on the burn rates of the JA-2 solid granular propellant. A series of experiments has shown an evidence of enhanced burn rate at pressures between 55 and 90 MPa (8,000 and 12,000 psi, respectively) over 400 mu s pulse length. A 20 to 40% enhancement in the burn rates has been observed when plasma is injected parallel to the surface of the propellant. When plasma is injected normal to the surface, the burn rate increases by about a factor of three. A set of experiments has been designed to measure the burn rates when the electrothermal plasma is injected at various angles, from 0 degrees to 90 degrees, to the surface of the propellant. Experiments were conducted at a constant input energy of 5 kJ+/- 2% to the electrothermal plasma source and constant base pressure of 15 Torr, which provides a 12,300 psi plasma pressure at the source exit close to the surface of the propellant. Results indicate increased burn rates with increased angle of injection. Optical emission spectroscopy measurement revealed a decrease in plasma temperature, at the plasma-propellant interface, with increased angle of injection. The plasma temperature at 90 degrees injection angle is about 30% less than that at 0 degrees. The temperature decrease may be attributed to increased burn rates at larger angles, which results in an increased effectiveness of the vapor shield plasma. the plasma density also decreases with increased angle of injection, but increases again at 90 degrees. There effects may also be due to increased neutral constituents at the plasma-propellant interface at larger injection angles. However, the plasma density at 90 degrees, where the burn rate is at a maximum, increases by approximately a factor of two higher than that of the source plasma.