The suppression of opposed-jet methane-air flames by methyl bromide

Abstract

An opposed-jet diffusion flame burner was used in conjunction with an emission infrared spectrometer to study the effects of the addition of methyl bromide on the combustion of methane with air. An optical system permitted incremental scanning of a laminar diffusion flame formed between two horizontally opposed burner tubes. The image of the flat flame was focused on an auxiliary slit of the spectrometer by optical mirrors and scanned by moving the slit passed the image. For a methane-air flame with an overall stoichiometric ratio, ø, of 0.86, the spectra for the 3700-2400 cm −1 region (H 2O, OH, CO 2, CH 3, and HCHO bands), and 2400 to 2000 cm −1 (CO and CO 2 bands) were compared with the spectra obtained when methyl bromide was added to the air-side of the burner. Supplementary measurements were made on methane-air and methaneoxygennitrogen flames with ø values in the range of 0.74–2.0. In some cases, the methane was diluted with nitrogen, and the methyl bromide was added to either the fuel or the air side of the burner. Enhancement of the CH 3 HCHO band intensity at 3000 cm −1, narrowing of the main reaction zone, and an increase in total emission of the recorded spectral regions were observed when methyl bromide was added to the flame. These results support those of cited experimental investigations and kinetic mechanisms for inhibition of methane combustion by methyl bromide.