Effect of dilution on laminar burning characteristics of H2/CO/CO2/air premixed flames with various hydrogen fractions

• We investigate the influence of CO2 dilution on H2/CO premixed flames under various hydrogen fractions.
• Markstein lengths are measured for H2/CO/CO2 mixtures.
• Laminar burning velocities are measured for H2/CO/CO2 mixtures.
• The thermal effect, diffusion effect and chemical effect on laminar burning velocity of H2/CO/CO2 mixtures are discussed.

The laminar burning characteristics of syngas-premixed (H2/CO/CO2/air) laminar spherical flames have been systematically investigated through an experiment using Schlieren system. In the experiment, the volume fraction of H2 in the H2/CO part of the H2/CO/CO2/air mixtures was varied from 30% to 100%, the volume fraction of CO2 in the H2/CO/CO2 mixtures was varied from 0% to 60%, and the equivalence ratio was varied from 0.4 to 1.0. The effects of hydrogen fraction, carbon dioxide fraction and equivalence ratio on flame propagation, Markstein length, and laminar burning velocities have been studied. The obtained laminar burning velocities were compared with existing data from the literature and excellent agreement was obtained. The flames become more unstable by decreasing the equivalence ratio and increasing dilution fraction. The value of laminar burning velocity decreases apparently with the increase of carbon dioxide dilution fraction due to combined effect of decrease in adiabatic temperature, thermal diffusivity and the CO2 participation in the chemical reaction of CO + OH ↔ CO2 + H. With the increase of hydrogen fraction, the laminar burning velocity increases significantly due to the chemical effect and diffusion effect rather than thermal effect.