Combustion behavior and flame structure of XM46 liquid propellant

This investigation was focused on the combustion behavior of XM46. Regression rate of XM46 has been characterized up to 207 MPa, displaying a complex burning behavior with both negative pressure exponent and plateau-like behavior. The flame structure displayed 3 different stages: 1) nearly simultaneous decomposition of both HAN and TEAN initiating in the liquid to produce gases around 300 °C, 2) break-down of heavy opaque intermediate molecules into transparent species, and 3) reaction of transparent species to form final products in the luminous flame. The feeding tests showed peculiar flashback phenomena, believed to be related to the interaction between gas-phase radicals and unbumed liquid propellant. Pyrolysis tests of XM46 were conducted in a specially designed pyrolyzer used in conjunction with a gas chromatograph/mass spectrometer. The major pyrolysis products observed were NO, N₂O, N₂, CO₂, CO, H₂O, HCN, and C₂H₄ when pyrolyzed at temperatures between 130 and 540 °C. The pressure dependency of the burning rate of the HAN-based liquid propellant is highly nonlinear. Water evaporation has a noticeable effect on combustion characteristics of XM46. Gas dissolution/desorption could also affect the burning rate. The type of fuel ingredient was found to have a significant effect on the overall burning characteristics.