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Spectroscopic investigation of nitromethane flames

: Eckl, W.; Weiser, V.; Weindel, M.; Eisenreich, N.


Propellants, explosives, pyrotechnics 22 (1997), Nr.3, S.180-183
ISSN: 0340-7462
ISSN: 0721-3115
ISSN: 1521-4087
Fraunhofer ICT ()

To get insights into the propellant combustion process nitromethane Pool Fire Flames were investigated analyzing both, the radiation emitted from intermediate combustion radicals (diat. mols.) in the UV and visible (VIS) spectral range, and the near IR spectra dominated by broad water bands. Comparing the UV/VIS spectra to calcd. band profiles, rotational and vibrational temps. (Trot, Tvib) of OH, NH, and CN were detd. At local thermal equil. Trot and Tvib must be equal. The detd. temps. show that the OH and NH emissions originate from pure thermal excitation (Trot=Tvib=2300-2380 K) but the CN emissions show addnl. a chem. excitation indicated by different vibrational and rotational temps. in the Boltzman factor (Trot=2100 K, Tvib=300 K). For a more detailed flame study, the emission of OH radicals was investigated more extensively by monitoring a 2-dimensional rotational temp. and emissivity profile. In cooler flame regions, the obsd. spectra are dominated by the near IR radiation emi tted from stable combustion products like water and CO2. Therefore, NIR spectra (1000-2500 nm) were compared to broad band profiles calcd. with a self-developed code based on the data of the "Handbook of IR Radiation of Combustion Gases". The flame temps. obtained by this method range from 1800-1900 K. The results are correlated to flames of CH4/NO2 which emit similar spectra indicating similar reaction mechanisms in the gaseous phase.