Flame Front Observation of Ammonia Decomposition and Oxidation Using 193 nm Two-Photon Photolysis and Photofragment Fluorescence

Abstract

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.