A Kinetic Modeling Study Of Biogas Combustion

Energy and environmental problems have prompted people turning to bioenergy, and of all the biofuel technology roadmap, biogas is the most mature one. Currently, more common utilization way of it is to convert it into other forms of energy by combustion, which makes the related kinetic modeling study very important for the promotion of biogas. In this paper, a deep research on the kinetic modeling of biogas combustion has been made, in order to get a better understand of its combustion property and internal mechanism.In this paper, firstly an original hydrogen and methane model have been made, then validated by the targeted experimental data from literature, such as concentration profile from JSR, ignition delay time from shock tube and flame speed. The final hydrogen kinetic model consists of 6 elements, 21 radicals and 59 reactions, and the final methane one consists of 6 elements, 56 radicals and 355 reactions. Sensitivity analysis is made for all the sub-mechanism, and the modeling results shows that the new models have a better predicition ability for most of the experimental data than the models from literature.Secondly, the new hydrogen and methane model were used for the research on the flammability of hydrogen, methane, and methane/water mixture under air environment with PREMIX code separately. The results shows that the span between the high percent and low percent corresponding to the rich and lean flammability limit of hydrogen and methane would be narrowed with the decrease of the pressure, until they meet at the lowest pressure, which is 0.085 bar for hydrogen and 0.05 bar for methane. In the system consisting of water, air and methane, the flammable area of methane would be smaller with the increase of water content. When the water content exceeds 25.35%, this system would never be burned.Lastly, an effect study of H₂O on NO_x emission during the marsh gas combustion was conducted by comparing the physical and chemical effect with the methane kinetic model. The result shows that the addition of H₂O would decrease the flame temperature, reducing the NO emission substantially, and owing to the chemical effect of H₂O, it would be reduced again. The physical effect of H₂O would inhibit all four NO routines, and the chemical effect would produce a second-inhibition effect on the prompt one, while enhance the thermal one slightly.