CH4/CO/H2/AIR混合燃氣之層流火焰速度分析

The major combustible constituents in the fuel gas produced by gasification of biomass are carbon monoxide, hydrogen and small amounts of methane. This thesis researched the laminar flame speed variation of methane added with the mixtures of carbon monoxide and hydrogen ([CO]: [H2]=2:1, [CO]:[H2]=1:1) at the stoichiometric condition. A simple tube method was adopted. The premixed flame propagation speed and the area of flame front were estimated to determine the laminar flame speed, and the shifting of the reaction path was discussed. The experimental results showed that the flame propagation speed in the tube and the laminar flame speed increased with the amount of the addition of CO/H2 mixture in methane fuel, and the amount of hydrogen in the mixture further increased the flame propagation speed and laminar flame speed. Unlike the observed deceleration of flame speed at methane mixed with high percentages (>80%) of CO, the flame speeds were continue increasing at the high CO/H2 addition in methane conditions. In order to interpret the phenomenon, this research used CHEMKIN v3.6 with GRI-3.0 to simulate the experimental conditions. The analysis results showed that the peek H atom concentrations at different CO addition followed the same trend as that of the laminar flame speed variations, and the concentration of O2 and O in flame increased with the amount of CO addition for their low consumption rates in the direct reactions with CO. The gas phase termination reaction H+O2+M HO2+M was then competed with the major branching reaction H+O2 OH+O at high O and O2 concentrations environment resulted in lower OH production in the system, thus to decrease the rate of reaction OH+CO H+CO2 and the laminar flame speed. In the above described mechanism, the insufficient H atom concentration in methane/CO mixtures was changed through adding H2 into the mixtures. The net reaction rate of H+O2 OH+O accelerated with H2 addition, and the system produced more OH to oxidize CO through OH+CO H+CO2 so as to steadily increase the laminar flame speed.