Effect of H2/CO ratio and N2/CO2 dilution rate on laminar burning velocity of syngas investigated by direct measurement and simulation

Laminar burning velocities of syngas/air premixed flames, varying with H-2/CO ratio (from 5/95 to 75/25) and N-2 or CO2 dilution rate (from 0% to 60%), were accurately measured using a Teflon coated Heat Flux burner and OH-PLIF based Bunsen flame method. Experiments were carried out at atmospheric pressure and room temperature, with fuel/air equivalence ratios ranging from fuel-lean to fuel-rich. Coupled with experimental data, three chemical kinetic mechanisms, namely GRI-Mech 3.0, USC Mech II and Davis H-2-CO mechanism, were validated. All of them can provide good prediction for the laminar burning velocity. The laminar burning velocity variations with H-2 and dilution gas contents were systematically investigated. For given dilution gas fraction, the laminar burning velocity reduction rate was enhanced as H-2/CO ratio increasing. Effects of the syngas components and equivalence ratio variation on the concentrations of radical H and OH were also studied. It appears that there is a strong linear correlation between the laminar burning velocity and the maximum concentration of the H radical in the reaction zone for syngas. This characteristic is exclusively different from that in methane air premixed flame. These findings indicated that the high thermal diffusivity of the H radical played an important role in the laminar burning velocity enhancement and affected the laminar burning velocity reduction rate under dilution condition. (C) 2014 Elsevier Ltd. All rights reserved.