Laser-induced fluorescence measurements of nitric oxide formation in high-pressure premixed methane flames

We have obtained quantitative LIF measurements of NO concentration in the postflame zone of a series of flat, laminar, premixed CH4/O-2/N-2 flames (0.5 less than or equal to phi less than or equal to 1.6) at pressures ranging from 1-14.6 atm. The temperatures of the flames were 1660-1960 K, indicating that prompt NO was the primary pathway for NO formation in the majority of these dames. In addition, we have modeled many of the experimental flames using the chemical reaction mechanism of Glarborg-Miller-Kee as modified by Drake and Blint (GMK-DB). This model accurately predicts the behavior of NO with increasing pressure and shows reasonable quantitative agreement for many of the flames at pressures less than or equal to 6.1 atm. At pressures greater than 6.1 atm, inaccuracies in the predicted temperature field preclude good quantitative agreement between the modeled and measured NO concentrations. Detailed NO measurements in ultra-lean (phi = 0.55-0.8) flames showed higher NO emissions with increasing pressure, a result consistent with kinetic modeling of these lean flames via the GMK-DB mechanism.