The Effects of CO2 Variation on Hydrodynamic and Thermal Diffusive Stability of Biogas–Air Flame

Abstract

Understanding the effects of CO2 on biogas combustion is vital as it occurs naturally as one of the major biogas content aside from CH4. In the present study, burning rate and flame stability of simulated biogas combustion have been investigated at 1 atm and 298K. CO2 dilution was set at 20, 40 and 50% to emulate typical biogas content. Experiment was performed using spherically expanding flame to include the effect of stretch on flame propagation. Results from experiment were compared with numerical results as well as data and correlations from literature. Results reveals a linear trend between CO2 dilution and burning rate reduction. Compared to pure CH4, peak burning rate steadily decreases to 21.17%, 34.14% and 45.15% as CO2 dilution was increased from 20 to, 40 and 50% respectively. Chemically, CO2 could slow down the reactions that produces OH and CO radicals important for CH4 dissociation. Physically, CO2 could modify mass and thermal diffusion pattern as indicated by the Markstein length that shows noticeable changes as CO2 was increased. In terms of stability, CO2 tends to stabilize flame by suppressing the thermal-diffusive and hydrodynamic instability.