MEASUREMENTS OF THE STRUCTURE OF LAMINAR, PREMIXED FLAMES OF CH4/NO2/O2 AND CH2O/NO2/O2 MIXTURES

This article describes experimental measurements of the structure of lean, premixed, laminar, flat flames of CH4/NO2/O2 and CH2O/NO2/O2 mixtures at 55 torr. The compositions of stable species in the flames were measured using a cooled quartz sampling microprobe and gas chromatographic analysis. The compositions of the intermediates OH, CN, CH, NH, and NH2 were measured by laser-induced fluorescence spectroscopy using an excimer laser pumped tunable dye laser system. Flames with only O2 as oxidizer were blue/violet due to C2 and CH emission or CO chemiluminescence. Flames with NO2 and O2 have two luminous zones, one yellow and the other blue/violet, separated by distinct, dark nonluminous zones. Nitrogen dioxide is a poor oxidizer in comparison to O2 and, therefore, rich mixtures with NO2 could not be stabilized. With CH4 as the fuel the products contain considerable unreacted NO2, along with NO and N2 whereas with CH2O as the fuel little N2 was formed. A partial reaction mechanism is discussed which accounts for the observations in the flame data.