Laminar burning velocities and flame stability analysis of H2/CO/air mixtures with dilution of N2 and CO2

Experimental measurement of the laminar burning velocities of H2/CO/air mixtures and equimolar H2/CO mixtures diluted with N2 and CO2 up to 60% and 20% by volume, respectively, were conducted at different equivalence ratios and conditions near to the sea level, 0.95 atm and 303 ± 2 K. Flames were generated using contoured slot-type nozzle burners and Schlieren images were used to determine the laminar burning velocity with the angle method. Numerical calculations were also conducted using the most recent detailed reaction mechanisms for comparison with the present experimental results. Additionally, a study was conducted to analyze the flame stability phenomenology that was found in the present experiments. The increase in the N2 and CO2 dilution fractions considerably reduced the laminar burning velocity due to the decrease in heat release and increase in heat capacity. At the same dilution fractions this effect was higher for the case of CO2 due to its higher heat capacity and dissociation effects during combustion. Flame instabilities were observed at lean conditions. While the presence of CO in the fuel mixture tends to stabilize the flame, H2 has a destabilizing effect which is the most dominant. A higher N2 and CO2 dilution fraction increased the range of equivalence ratios where unstable flames were obtained due to the increase in the thermal-diffusive instabilities.