Laser recoil combustion response of HNF oxidizer from 1 to 6 atmospheres

Abstract

Solid oxidizer HNF, hydrazinium nitroformate, crystals were pressed into pellets and burned as a monopropellant in the laser recoil device at pressures from 1 to 6 atm. The laser flux was set at 2 different mean power levels with sinusoidal oscillations of 21 ± 11.5 W/cm2 or 52 ± 5.9 W/cm2. Oscillations were logarithmically swept over the range from 4 to 80 Hz. A Russian inductive force transducer was used in these tests. The force transducer has a resonant frequency at 140 Hz, but performs well at frequencies below 100 Hz. HNF pellets were inhibited with a glass ring on the sample pedestal. HNF burns nicely with a steep burn rate slope of 0.892 down to 5 psia. Burn rate vs. laser flux was measured up to 60 W/cm2 at 1,2, 3,4, and 6 atm pressure. The slope of the bum rate vs laser flux was nearly the same at each pressure. At one atmosphere the rate vs. flux slope of HNF is slightly lower than HMX and about the same rate as HMX. Ignition times decreased from 760 ms to 78 ms as the laser flux increased from 21 to 67 W/cm2. Ignition times also decreased as pressure increased. HNF thrust oscillations decreased from 65 to 20 mg/cm2 over the frequency range of 4 to 80 Hz. The thrust oscillations also decreased 50% in amplitude as the pressure increased to 4 atm. The thrust oscillations are about the same order of magnitude as for HMX, less than N5 and greater than RDX. A phase crossover frequency was not determined as it was below the 4 Hz frequency range of these tests. The phase lag decreased very slightly with pressure, but was nearly the same at low frequencies.