Experimental and Numerical Study on Laminar Flame Characteristics of Methane Oxy-fuel Mixtures Highly Diluted with CO₂

Abstract

An experimental and numerical study on laminar flame characteristics of methane oxy-fuel mixtures highly diluted with CO 2 was conducted using a constant volume chamber and CHEMKIN package. The effects of high CO 2 dilution on combustion chemical reaction, flame instability, and flame radiation of CH 4 /CO 2 /O 2 mixtures were studied. The laminar burning velocities of CH 4 /CO 2 /O 2 mixtures decrease with the increase of the CO 2 fraction. CO 2 directly participates in the chemical reaction through the elementary reaction OH + CO = H + CO 2 and inhibits the combustion process by the competition of the H radical between the reverse reaction of OH + CO = H + CO 2 and the reaction H + O 2 = O + OH. This effect is more obvious for highly diluted CO 2 in the case of CH 4 /CO 2 /O 2 mixtures. CO 2 suppresses the flame instability by the combined effect of hydrodynamic and thermal-diffusive instabilities. The radiation of CH 4 oxy-fuel combustion is much stronger than that of CH 4 /air combustion mainly because of the existence of a large fraction of CO 2 in CH 4 /CO 2 /O 2 flames, which will influence the wall temperature and temperature distribution in the gas turbine combustor.