CH4/CO/AIR混合燃氣之火焰速度分析

Abstract

The major combustible components in the gasified products of biomass are hydrogen, carbon monoxide, and methane. To fully utilize the gasified products, a detailed understanding of the combustion characteristics of the product mixtures is crucial. This thesis research focused on the combustion of the mixtures of methane and carbon monoxide. By using a self-designed tube method, the flame propagation speeds in the tube were measured. Coupled with the flame area estimation, the laminar flame speeds were deduced at different equivalence ratio (ψ= 0.85,1.0,1.15) and different mixing ratios of Methane and carbon monoxide. The experimental results indicated that the flame propagation speeds as well as the deduced laminar flame speeds increased initially with the amount of carbon monoxide in the mixtures, and, a peak propagation speed and a peak flame speed were observed for 85%CO and 80%CO mixtures, respectively. The observed maximum laminar flame speed for CH4/CO mixtures was 54.3cm/s at equivalence ratio of 1 and 80%CO content. Further increase the amount of carbon monoxide, the flame speed started to drop. Flame area also increased with increasing amount of carbon monoxide. Caused by heat transfer and buoyancy effects, flame area was also developed to a peak value at 85%CO in the mixture. In conjunction with GRI-3.0 mechanism, detailed reaction kinetic modeling of the mixtures was performed using Chemkin 3.6. The results showed that the addition of CO into CH4 increased the amount of free radicals in the flame, and the flame temperature raise as well to make the laminar flame speed increase. However, mixtures with more than 80%CO produced less amount of OH for low concentration of O2 in the system, thus decrease the rate of the major heat release reaction OH + CO CO2 + H as well as the laminar flame speed.