Experimental Study of Biogas Flame Stability in Laboratory Coaxial Burners and Domestic Gas Stoves

The current energy context raises the awareness to search for renewable energy sources to lower the dependence on the fossil fuels in our energy mixes and go toward a more sustainable future. Biogas, a renewable fuel obtained from the biological breakdown of biomass, has gained a significant interest lately due to its similarity with CH4. However, because of its high CO2 content, the combustion of this renewable fuel faces a variety of instabilities such as blow-off and liftoff. In this study, the effect of CO2 addition and burner geometry on the laminar combustion of biogas is investigated. For this purpose, the range of CO2 in the fuel was varied from 0% to 70% while maintaining the flame power at 1 kW. an ICCD camera coupled with OH* filter was used to study the chemiluminescence and the effect of the mentioned parameters on the flame front and the combustion characteristics. Four different type of burners (laboratory burners, propane/butane stove, natural gas stove, and biogas stove) are used to assess the geometry effects on the biogas combustion and to determine the range of operating conditions, CO2 in particular, of every gas stove. A gas analyzer is used to measure the NOx and CO emissions. The experiments using the laboratory burners show that the increase in CO2 in the blend enhanced flame instability and increased the liftoff height while the increase in the burner’s diameter helped stabilize the flame and delayed the liftoff. It was also found that the addition of CO2 increased CO and decreased NOx emissions in exhaust gases. The results of biogas combustion in different gas stoves demonstrated that they are not compatible for sustaining a stable flame of the biogas with a high content of CO2 as the blow-off started at 20% CO2 for propane/butane, at 40% for natural gas stove and at 70% CO2 for the biogas stove. The OH* chemiluminescence images show how the CO2 content changed the flame front and altered the combustion chemistry. These findings highlighted the effect CO2 proportion in the biogas mixture on flame behavior for different burners, it is challenging to use the commercial stoves the biogas.