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.

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An experimental and numerical study on thermal and chemical effects of water vapor addition on the laminar burning velocities of syngas was conducted using a constant-volume chamber and CHEMKIN package. The experimental conditions in the present study for CO/H2/air/H2O mixtures with hydrogen fraction in syngas were from 5% to 50%, initial temperature of 373 K, pressures of 0.1 and 0.5 MPa and water dilution ratios from 0% to 30%. The measured laminar burning velocity data were compared with simulations with three mechanisms, the San Diego mechanism and those of Davis et al. and Li et al. The experimental data showed a reasonable agreement with the calculated values at low and high pressures when the content of H2 in the fuel was low. However, when H2/CO ratio in the fuel was higher (75/25 and 95/05), all three mechanisms overpredicated the laminar burning velocity for fuel-rich mixtures. Sensitivity analysis was performed to identify the possible sources of discrepancy between the experimental data and calculated results. Furthermore, chemical effects of H2O on the laminar burning velocities at various CO/H2 ratios when water was added into the mixtures were studied. For syngas with CO/H2 ratio of 50/50, water had a weak inhibiting effect on the chemical reaction of the mixtures. For the higher CO/H2 ratios, water addition accelerated the chemical reaction and this positive effect became more significant for the syngas with the increased CO/H2 ratio. Different trends were explained using the consumption path analysis.

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