Comparison of laser and pressure-driven thrust measurements for HMX

Unsteady thrust response of HMX was measured during laser and pressure-driven combustion. A CO₂ laser was used as a heating source to ignite and sustain propellant combustion during pressure-driven tests by providing a constant heat flux. The laser acted as a source of ignition and oscillatory heat flux during laser-driven combustion. The laser-driven tests were performed at frequencies ranging from 3.9 to 250 Hz. Mean incident laser heat fluxes of 35, 60 and 90 W/cm² were used. Pressure-driven thrust measurements were made in a different chamber with a 10% peak-to-peak pressure variation about the mean. The driving frequencies ranged from 4 to 100 Hz. Tests were conducted with air as the ambient gas at atmospheric pressure. The thrust response amplitude and phase as a function of frequency and heat flux were collected under both test conditions. A, B, n and n_s parameters were obtained from the experiments and compared to theoretical values.