Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO2 on the laminar burning velocity and flame stability of syngas fuel (50% H2–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ϕ = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H2–CO–CO2–O2–N2 mixtures, the peak burning velocity shifts from ϕ = 2.0 for 0% CO2 in fuel to ϕ = 1.6 for 30% CO2 in fuel. For H2–CO–O2–CO2 mixtures, the peak burning velocity occurred at ϕ = 1.0 unaffected by proportion of CO2 in the mixture. If the mole fraction of combustibles in H2–CO–O2–CO2 mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H2–CO–O2–CO2 and H2–CO–O2–N2 mixtures suggested that CO2 has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO2 could be due to the active participation of CO2 in the chemical reactions through the following intermediate reaction CO + OH ↔ CO2 + H.