The Behaviour of Biogas Containing Carbon Dioxide in Spark Ignited Premix Combustion at Various Pressures

Biogas is an alternative energy source that is sustainable and renewable containing more than 50% methane (CH4) and its biggest impurity or inhibitor is carbon dioxide (CO2). Demands for replacing fossil fuels require an improved fundamental understanding of its combustion processes and flammability limits and laminar burning velocities are important characteristics in this process. Thus, this study focused on the effects of carbon dioxide (CO2) on biogas flammability limits and laminar burning velocities in spark ignited premix combustion. Spark ignited spherical combustion bomb was used for the biogas combustion. Spherically expanding laminar premixed flames, freely propagating from spark ignition in initially quiescent biogas–air mixtures, were continuously recorded by a high-speed digital camera. The combustion bomb was filled with biogas-air mixtures at various pressures, CO2 levels and equivalence ratios (ϕ) at ambient temperature. The results were also compared to those of the previous study into inhibitorless biogas (biogas without carbon dioxide inhibitor) at various pressures and equivalence ratios (ϕ). Either the flammable areas become narrower with increased percentages of carbon dioxide or pressure become lower. Biogas with 50% CO2 content, there was no biogas flame propagation at reduced pressure (0.5 atm) and various equivalence ratios. The results show that the laminar burning velocity at the same equivalence ratio declined in respect with the increased level of carbon dioxide. The laminar burning velocities were higher at the same equivalence ratio by reducing the initial pressure.