The effect of CO₂ fraction on the flame stability of biogas premixed flame

This study aimed to determine the effect of CO₂ on flame structure and stability of premixed flames biogas using counterflow flame configuration. In this research, the CO₂ fraction in Biogas was varied from 0% to 50%. The total mass flow of gas flowed from both combustion nozzle was varied within 6 L/min and 8 L/min. The burning behavior of biogas counterflow flames were photographed by digital camera. Besides, the stability limit of counterflow diffusion flame was characterized by the minimum oxygen concentration at extinction. The results showed that the CO₂ content in the biogas affect the characteristics of premixed flame, especially the change of a blue flame to blue flame with lower luminosity when increasing CO₂ concentration. On the other hand, the variation in the oxygen concentration has more significant effect on the dimension of the premixed flame compared to the effects of the CO₂ content in the biogas. The flash back phenomena exist in the counterflow premixed flame when the equivalence ratio of reactant closes to 1. It means that the biogas combustion is recommended to be done in the equivalence ratio close to 1 in order to obtain the best combustion performance. The results also showed that the highest concentration of oxygen minimum to keep the biogas premixed flame remained stable occurred in the percentage of CO₂ in the biogas is 30%. This result could be explained based on the composition of unburned CH₄ and CO₂ gas in the combustion process.