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 pr essures ranging from 1-14.6 atm. The temperatures of the flames were 1 660-1960 K, indicating that prompt NO was the primary pathway for NO f ormation 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 m odel accurately predicts the behavior of NO with increasing pressure a nd shows reasonable quantitative agreement for many of the flames at p ressures less than or equal to 6.1 atm. At pressures greater than 6.1 atm, inaccuracies in the predicted temperature field preclude good qua ntitative agreement between the modeled and measured NO concentrations . Detailed NO measurements in ultra-lean (phi = 0.55-0.8) flames showe d higher NO emissions with increasing pressure, a result consistent wi th kinetic modeling of these lean flames via the GMK-DB mechanism.