NO concentrations in laminar premixed CH4/O2/N2 flames with varying equivalence ratio

Number density and concentration of nitric oxide have been investigated in laminar premixed CH4/O2/N2 flames using laser-induced fluorescence technique. Emphasis was placed on quantitative measurements, which were taken in flames at various equivalence ratios ranging from 0.9 ∼ 3.0. The flow rate was fixed at 2 SLPM. The NO A-X (0,0) vibrational band around 226 nm was excited using a XeCl excimer-pumped dye laser. By selecting an appropriate NO transition, the interferences from elastic scattering and O2 fluorescence were minimized. Results show that the maximum NO concentration increased at the range of equivalence ratio from ϕ = 0.9 to 1.6, decreased from ϕ = 1.6 to 2.0 and slowly increased with increasing equivalence ratio above ϕ = 2.0. Also, the maximum NO concentration was at around the reaction zone.