Effect of inhibitors on biogas laminar burning velocity and flammability limits in spark ignited premix combustion

Biogas is the natural byproduct of the decomposition of vegetation or animal manure, of which there are almost in exhaustable supplies in the world, and which does not contribute CO2 or other greenhouse gases to global warming or climate change. Biogas contains 66.4% flammable gas (CH₄) and 33.6% inhibitors (CO₂ and N₂). This study focuses on the effects of inhibitors on biogas laminar burning velocity and flammability limits in spark ignited premix combustion. Spherically expanding laminar premixed flames, freely propagating from spark ignition sources in initially quiescent biogas-air mixtures, are continuously recorded by a high-speed digital camera. Initially, all the experiments in this paper were performed using inhibitorless biogas (biogas without inhibitors) at room temperature, at reduced pressure (0.5 atm) and at various equivalence ratios (φ) from the lower flammable limit to the upper flammable limit. The results are compared with those from biogas (containing inhibitors) flames at reduced pressure, inhibitorless biogas flames at atmospheric pressure (1 atm), and biogas flames at atmospheric pressure to emphasize the effect of inhibitors on biogas laminar burning velocity and flammability limits. Compared to an inhibitorless biogas-air mixtures, in the biogas-air mixtures, the presence of inhibitors cause a reduction in the laminar burning velocity and the flammable limits become narrower.