Abstract:

Laser-induced fluorescence (LIF) techniques have previously provided two-dimensional images of nitric oxide concentrations in practical combustion systems. However, at pressures above 10 atmospheres, attenuation of the excitation laser in the hot combustion gases and interference from molecular oxygen LIF causes significant problems for NO LIF using transitions in the D-X (0,1) and A-X (0,0) bands. The use of A-X(0,2) excitation significantly reduces the laser attenuation and influence from interfering species but in turn may have problems from the large temperature dependence of the population in the probed ground state. We present here detailed spectroscopic studies to determine the suitability of techniques based on NO A-X (0,1) excitation. We report measurements in laminar premixed methane/air flames at pressures between 1 and 60 bar, and based on these results, we discuss the advantages and problems of the A-X(0,1) system (excited at 235 - 237 nm) and compare this strategy with the A-X(0,2) and (0,0) excitation studied earlier.