Laser recoil combustion response of N5 propellant from 1 to 9 atmospheres

Abstract

The combustion response of N5-catalyzed double-base propellant was experimentally measured at 1.2, 3, 4, 6, and 9 atm using the laser recoil technique. Tests were done using a logarithmic frequency sweep controller to gain maximum data from each test. Sample burn rate at a mean heat flux of 35 W/cm2 and 1 atm was 1.3 mm/s. The CO2 laser power was monitored in real time using a fast response HgCdTe room temperature detector. The effects of pressure (1–9 atm) and oscillation amplitude (±9, 15, and 25 W/cm2) on the response function were measured. Steady-state burn rate data at low pressure was measured. The slight pressure rise inside the combustion tank caused an upward drift in the force transducer signal. Light oscillations generally changed from lead to a lag of over 100 degrees as frequency changed from 10 to 50 Hz. At a constant pressure, thrust oscillation levels increased as the laser power oscillation level was increased. The cross from phase lead to lag seemed to decrease in frequency as the power oscillation amplitude increased. At constant pressure, the light amplitude response broadened as the power oscillation amplitude increased and the phase crossover moved to a slightly lower frequency. Thrust oscillation amplitudes decreased as the pressure increased to 75 psi, above which they became insignificant at these low heat flux levels. Thrust phase lead increased as the pressure was increased. Light oscillations increased as the pressure increased, due to the flame zone moving closer to the propellant surface.