A computational study of combustion and extinction of opposed-jet syngas diffusion flames

This paper reports a numerical study on the combustion and extinction characteristics of opposed-jet syngas diffusion flames. A model of one-dimensional counterflow syngas diffusion flames was constructed with constant strain rate formulations, which used detailed chemical kinetics and thermal and transport properties with flame radiation calculated by statistic narrowband radiation model. Detailed flame structures, species production rates and net reaction rates of key chemical reaction steps were analyzed. The effects of syngas compositions, dilution gases and pressures on the flame structures and extinction limits of H2/CO synthetic mixture flames were discussed. Results indicate the flame structures and flame extinction are impacted by the compositions of syngas mixture significantly. From H2-enriched syngas to CO-enriched syngas fuels, the dominant chain reactions are shifting from OH + H2→H + H2O for H2O production to OH + CO→H + CO2 for CO2 production through the key chain-branching reaction of H + O2→O + OH. Flame temperature increases with increasing hydrogen content and pressure, but the flame thickness is decreased with pressure. Besides, the study of the dilution effects from CO2, N2, and H2O, showed the maximum flame temperature is decreased the most with CO2 as the dilution gas, while CO-enriched syngas flames with H2O dilution has highest maximum flame temperature when extinction occurs due to the competitions of chemical effect and radiation effect. Finally, extinction limits were obtained with minimum hydrogen percentage as the index at different pressures, which provides a fundamental understanding of syngas combustion and applications.

► We model the counterflow CO/H2 diffusion flames with flame radiation. ► We examine the flame structures, reaction rates and extinction characteristics. ► Flame temperature increases with increasing hydrogen content and pressure. ► The dominant reaction is shifting from OH + H2 → H + H2O to OH + CO → H + CO2 as CO is richer. ► The maximum flame temperature is decreased the most with CO2 dilution.