High-pressure combustion behavior of nitromethane

The combustion behavior of the nitromethane (CH₃NO₂) liquid monopropellant was studied using an ultra-high pressure strand burner (UHPSB), a liquid propellant.strand burner (LPSB), and a UV/Visible absorption spectrometer. This UHPSB facility was used to obtain burning rates for pressures up to 30,000 psi. Burning rate expressions were developed over a wide range of pressures. Three distinct regimes were observed: below approximately 15 MPa, the bum rate exponent was 1.03; above this pressure, it became abruptly steeper, to 2.33, and finally flattened to 0.86 for pressures between 70 and 170 MPa. A one-dimensional kinetic model based on the Chemkin-II library code using Melius’ nitromethane kinetics mechanism was adopted to obtain species and temperature profiles for the nitromethane flame. At 3.0 MPa, the main product species in declining order of mole fraction were CO, H₂O, H₂, N₂, and CO₂. The most important intermediate reactants were NO, CH₂O, NO₂, and HCN. A thin reaction zone of approximately 400 micrometers corresponded well with flame observations at similar conditions. UV/Visible absorption measurements using LP burning inside a square quartz sample cell corroborated the calculated low OH mole fraction.