IMPROVEMENT OF 2-PHOTON LASER-INDUCED FLUORESCENCE MEASUREMENTS OF H-ATOM AND O-ATOM IN PREMIXED METHANE AIR FLAMES/

Two-photon LIF is used to measure the concentration of H- and O-atom i n low-pressure premixed methane/air flames at different equivalence ra tios. New experimental evidences of photochemical effects, interferenc e and collisional energy transfer upon excitation at 205 and 226 nm ar e shown. At 205 nm, CH3 photodissociation is shown to be an important photolytic source of H atoms in the reaction zone of the methane flame s. At 226 nm, an efficient energy transfer between O(P-3) and N-2 is e stablished from the observation of O-resonant emissions from the secon d positive system of N-2. The subsequent rate of O(P-3) depletion appe ars to be essentially ''controlled'' by the O(P-3) concentration and i s probably only minimally temperature dependent. Finally quenching rat e coefficients for O(P-3) by water and nitrogen are deduced from quenc hing rates measurements performed in CH4/O-2/N-2 and CH4/O-2/Ar flames .