Behaviour of Biogas Containing Nitrogen on Flammability limits and Laminar Burning Velocities

Abstract

Biogas is a renewable energy and consists of up to 50% methane (CH₄) as a flammable gas and other inhibitors such as nitrogen (N₂) up to 10%, the second biggest impurity in it. Before it can be used as a substitution for fossil fuels, a basic understanding of its combustion processes in spark ignited combustion engines is needed. This research focused on the behavior of biogas containing N₂ on flammability limits and laminar burning velocities at various pressure. Biogas containing N₂-air mixtures was burned in a spherical bomb using spark ignition in the centre of the vessel (bomb). The spherical bomb was employed for this research, gases in various mixtures were injected into it by an absolute pressure transducer at pressures appropriate for the equivalence ratios required. Then, dry air was pumped in at the pressures needed. Biogas mixtures were centrally ignited and the propagated flame was recorded using a high speed camera. All biogas mixtures experiments were performed at ambient temperatures under different pressures as well as at different equivalence ratios. The outcomes were compared to the results of prior study into inhibitorless biogas. The outcomes indicated that the lesser the amount of N₂ in biogas, the greater the laminar burning velocities. And furthermore, that when initial pressures were reduced and equivalence ratios were the same, laminar burning velocities increased and that increasing N₂ levels at the same initial combustion pressures did not influence the flammability limits of biogas.