Laser recoil, plume emission, and flame height combustion response of HMX and RDX at atmospheric pressure

Abstract

The laser recoil technique was used to measure the combustion response of neat HMX and RDX atatmospheric pressure in air. Heat flux was modulated approximately sinusoidally at frequencies from 2.5 to 1000 Hz and heat fluxes of 8–52 W/cm 2 . Thrust, light emission, and flame position were measured simultaneously so that amplitude and phase relationships could be determined as a function of frequency. Thrust was measured using a microforce transducer, light emission was measured by photo diode, and the flame height was photographed using a gated intensified charge coupled device (CCD) camera. The CCD camera recorded CN radical chemiluminescence, which is a measure of flame structure for the final (secondary) flame sheet. HMX had a broad flat thrust response, suggesting that the recoil technique needs further improvement.HMX had a light emission resonance at 10 Hz. RDX thrust and light emission oscillations were about half the amplitude of HMX. Monopropellant burn rates were 0.080 cm/s and 0.054 cm/s for HMX and RDX, respectively. HMX flame height was found to vary sinusoidally with phase angle, having a response peak between 8 and 50 Hz and crossing from phase lead to phase lag at about 20 Hz. The flame height response function of HMX was similar to light emission response. The resonant peak occurred at approximately the same frequency, the phase reacted the same as a function of frequency, and no unusual effects were seen at high frequency. Based on this data, the flame is reasonably quasi-steady below 40 Hz, in that the difference in phase lag between thrust and flame oscillations is less that 30° with almost no difference at the response peak of 10–20 Hz.