The Effects of CO2 Dilution on Spherical Premixed Methane Flames

The purpose of this paper is to investigate the combustion properties of CH₄/O₂ mixtures diluted by CO₂ compared to those of CH₄/O₂/N₂ mixtures to study the feasibility of the new combustion method, which is expected to be effective in NO_x reduction and the improvement of combustion. Both experimental and numerical studies are conducted to scrutinize the effects of flame stretch on the burning velocity, which plays an important role in combustion performance not only for laminar flames but also for turbulent flames. In this study, experiments are conducted by using a spherical combustion bomb for applications to internal combustion engines. Then the effects of flame stretch are also investigated numerically and quantitative discussion is made in terms of Markstein number which represents non-dimensional sensitivity of the burning velocity to flame stretch. As a result it is found that Markstein numbers for both methane mixtures decrease with decreasing equivalence ratio. In addition CH₄/O₂/CO₂ mixtures have the low values of Markstein number compared with CH₄/O₂/N₂ mixtures over the whole equivalence ratio.