Laminar Burning Characteristics Of Biogas-Air Mixtures In Spark Ignited Premix Combustion

摘要

Laminar burning velocities of biogas-air mixtures in premixed combustion have been studied toudelucidate the fundamental flame propagation characteristic of biogas as a new alternative and renewable fuel.udThe results are compared with those from a methane-air flame. Biogas is a sustainable and renewable fuel that isudproduced in digestion facilities. The composition of biogas discussed in this paper consists of 66.4% methane,ud30.6% carbon dioxide and 3% nitrogen. Burning velocity was measured using a photographic technique in audhigh pressure fan-stirred bomb, the initial condition being at room temperature and atmospheric pressure. Basedudon this experimental investigation, the laminar burning velocities of biogas-air mixtures were 0.2086 m/s for leanud(�=0.8), 0.2638 m/s for stoichiometric (�=1.0) and 0.1864 m/s for rich (�=1.2) conditions. Compared to audmethane-air mixture, the presence of carbon dioxide and nitrogen causes a reduction in the laminar burningudvelocity for two reasons. The dilution effect leads to a lower concentration of reactive species in the fuel-airudmixture for a given equivalence ratio, which leads to a lower overall chemical reaction rate of bimolecularudreactions in the fuel oxidation reaction mechanism. Also, the presence of this additional inert gas will absorbudsome of the heat generated, thus lowering the flame temperature which in turn will tend to reduce the overall rateudof many of the chemical reactions within the fuel oxidation mechanism. These effects lead to a differentudbehaviour in burning velocity of biogas as a function of equivalence ratio. Whereas a rich (�=1.2) methane-airudmixture has a higher burning velocity than a lean (�=0.8) mixture, the reverse is the case for the equivalentudbiogas-air mixtures where the lean mixture has a higher burning velocity than the rich mixture. This is audconsequence of the rich biogas-air mixture having a higher fraction of the carbon dioxide and nitrogenudcomponents from the fuel compared to the lean biogas-air mixture, and shifts the optimum equivalence ratio forudoperation of a biogas-air mixture to a leaner mixture than would be the case for methane-air mixtures.