Combustion behavior and flame structure of nitromethane

Better knowledge of nitromethane (CH₃NO₂) flame structure and combustion behavior is desirable for a number of possible propulsion applications, both earth-based and extraterrestrial. When considered for rocket applications, nitromethane monopropellant is more energetic and less toxic than some current storable monopropellants such as hydrazine, though shock sensitivity questions still remain. In this investigation, the combustion behavior of nitromethane was studied using a variety of experimental and theoretical techniques over a broad range of pressures from 2.5 to 170 MPa. Its burning rates at different pressures were measured in quartz tubes and at a free surface, and found to fall into 3 regimes. At low pressures (4 to 6 MPa), temperature profile measurements using fine-wire thermocouples showed a thick thermal wave in the liquid subsurface, extremely thin flame zone, and final flame temperature of near 2,100 K, significantly less than the equilibrium value of 2,460 K. A model was formulated that included both gas-phase and condensedphase processes. Using the detailed reaction mechanism for nitromethane developed by Yetter and Rabitz coupled with the CHEMKIN code, flame structure was calculated and compared to observations and measured values. Significant differences were found; however, with the modification of kinetic parameters in two elementary reactions, the measured temperature trace was duplicated.