Effects of oxidizer composition on the structure of laminar coflow (CO-H2)/(O2/H2O) diffusion flames

The structures of laminar coflow syngas diffusion flames burning in O2/H2O atmosphere were experimentally and numerically studied at 1 atm and inlet temperature of 400 K. The effects of oxidizer composition on the attachment and fuel pyrolysis inside the fuel tube were investigated by varying the O2/H2O molar ratio from 20/80 to 100/0. The flame attachment phenomenon was captured using a digital camera, and a 2D flame code was adopted to model the thermal and chemical structures of laminar coflow syngas flames using detailed kinetics mechanism. Results show that increasing the O2/H2O ratio has little influence on the flame attachment since the diffusions of both the fuel components and O2 in the oxidizer were promoted. However, the temperature of the burner tip was significantly enhanced as O2/H2O ratio increases, and kinetics analysis shows that it is attributed to the promoted heat release rate of H + O2(+M) = HO2(+M). As the O2/H2O ratio increases, syngas pyrolysis inside the fuel tube is promoted, mainly through the H consumption reactions because of the enhanced back diffusion of H from the flame front into the burner.