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.
Ignition delay times of methyl propanoate (MP) were measured in a shock tube over the temperature range of 1040−1720 K, pressures of 1.2−10 atm, fuel concentrations of 0.5−2.0%, and equivalence ratios of 0.5−2.0. Through multiple linear regression, a correlation for the tested ignition delay times was obtained, and the measured data were also compared to the previous data. Two available MP models (Princeton model and Westbrook model), were used to simulate the experimental data. Results suggest that further modifications on the available MP models are necessary. The modified MP model, consisting of 318 species and 1668 reactions, was proposed on the basis of previous studies, and it gives better prediction on the MP ignition delay times under all tested conditions than those of the other two available models. The modified MP model was further validated against the MP pyrolysis data and laminar flame speeds, and reasonable agreements were achieved. Sensitivity analysis reveals that the small radical reactions play key important roles in MP high-temperature ignition, while some fuel-specific reactions also exhibit relatively large sensitivity coefficients. Reaction pathway analysis indicates that MP is dominantly consumed through the H-abstraction reactions.
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