Combustion regimes of syngas flame in a micro flow reactor with controlled temperature profile: A numerical study

Abstract

Flame characteristics of stoichiometric syngas/diluted-air mixture (CO:H2:O2:N2=1:1:1:7) in a micro-flow reactor with controlled wall temperature profile were numerically studied. In addition to single normal flame and single weak flame that respectively occur at high and low inlet velocities, two new combustion regimes, i.e., “coexistence of upstream normal flame and downstream weak flame (UNF-DWF)” and “uninterrupted flame with repetitive extinction and ignition (UFREI)”, were found at moderate inlet velocities. It is revealed that the coexisting downstream weak flame of UNF-DWF is attributed to incomplete consumption of CO by the upstream normal flame. Analysis of reaction path further demonstrates that the downstream weak flame of UNF-DWF is partially sustained by H2O through H2O+O=2OH due to H2O production in the upstream normal flame. To elucidate the dynamic process of UFREI, it is artificially divided into “upstream flame” and “downstream flame (actually an oscillating weak flame)”, and an entire period of UFREI is divided into four sub-regions. The temporal variations of CO mole fraction profile and heat release rate profile along the centerline of each sub-region are exhibited and analyzed. Briefly speaking, the formation of UFREIs is essentially a result of early re-ignition of residual CO from the upstream flame before the occurrence of its extinction. In summary, the present study sheds some light on the complicated combustion characteristics of syngas in the micro flow reactor with a prescribed wall temperature profile.