Flame front observation of ammonia decomposition and oxidation using 193 nm two-photon photolysis and photofragment fluorescence

The 193 nm output of an ArF laser is utilized in the detection of gas-phase ammonia in methane-air flames of varying stoichiometry. Photolysis of ammonia with the 193 nm radiation results in NH photofragment fluorescence-the intensity of which is found to be proportional to the concentration of the ammonia present. Detection limits of <1 ppm of gas-phase ammonia are readily achievable under atmospheric flame conditions, Two-dimensional images of ammonia decomposition have been obtained for a laminar premixed flame, clearly revealing the conical reaction zone. Thermal decomposition of the ammonia is observed in the pre-flame zone of the burner in addition to its oxidation in the reaction zone.