NOx emission and major species concentrations in partially premixed laminar methane/air co-flow jet flames

Measurements of visible flame heights, global radiative heat loss fractions, distributions of mole fractions of stable gas species, and pollutant emission indices in laminar partially premixed flames burning various fuel-rich mixtures of CH4 and air in an overventilating co-flow of air are reported. Mole fractions of CO2, CO, H-2, O-2, N-2, CH4, C2H4 and C2H2 were measured, using sampling and gas chromatography, at several radial locations at three different heights above the fuel tube for a fixed fuel flow rate and six different fuel tube equivalence ratios. Mole fractions of H2O were inferred from the dry based measurements. With increasing levels of partial premixing following effects are observed: (1) the visible flame height decreases and the overall flame color changes from yellow to blue; (2) the radiative heat loss fraction first decreases and then reaches a constant value; (3) the mole fractions of CO decrease and those of CO2 and H2O increase in the lean parts of the flame; (4) mole fractions of C2H2 decrease and those of C2H4 first increase and then decrease in the rich parts of the flame; (5) mole fractions of CO and H-2 first decrease slightly and then increase in the rich parts of the flame; and (6) the O-2 mole fractions at the point of negligible CH4 mole fraction decrease. Measurements of emission indices for NO, NOx, CO and HC show that, for a fixed fuel flow rate and overall equivalence ratio, an optimum level of partial premixing exists.