GENERATION OF CO AND SMOKE DURING UNDERVENTILATED COMBUSTION

The CO and smoke yields observed for underventilated laminar diffusion flames are presented for methane and ethene for global equivalence ratio PHI over the range 0.5 to 4.0. A Burke-Schumann type burner with fuel in the center tube and air in the annular region was used. The peak CO yields for methane and ethene, 0.37 and 0.47, respectively, are at least a factor of 100 greater than for overventilated burning. The ratio of CO/CO, versus PHI for the methane flame is compared with local measurements of this ratio for both overventilated and underventilated laminar diffusion flames and with the results for turbulent natural gas flames quenched in an upper layer. The peak smoke yields for methane at a flow rate of 10 cm3/s and for ethene at a fuel flow rate of 6.4 cm3/s are 0.01 and 0.05, respectively, compared with yields of 0.0 and 0.028 for the overventilated case. The proportionality between smoke yield and CO yield observed for overventilated burning for a wide range of fuels is found not to be valid for the under-ventilated case. The chemical makeup and structure of the smoke produced at high equivalence ratio is qualitatively different from smoke produced under overventilated conditions; the smoke is mainly organic rather than graphitic and it has an agglutinated structure rather than an agglomerate structure with distinct primary spheres usually observed in overventilated burning.