Experiments and Kinetic Modeling of High-Pressure Hydrogen/Oxygen Flames (with Carbon monoxide, Carbon dioxide, and Methane Addition)

Knowledge of the H2/O2 chemical kinetic model is relevant to many energy conversion applications for a variety of fuels. Not only does the H2/O2 kinetic model serve as an essential submodel for all hydrocarbon and oxygenate fuels, but also there has been considerable recent interest in H2 (pure or mixed with CO, CO 2, H2O, and gaseous hydrocarbons as "syngas") as a fuel itself in emerging clean coal technologies. At present, our understanding of combustion behavior of H2 and all other fuels is most limited at higher pressures and lower temperatures -- the conditions at which most advanced engines operate. The objectives of the present study are to measure relevant combustion properties of and develop a kinetic model for H2 and syngas-relevant mixtures in high-pressure, dilute flames.;Experimental measurements of burning rates, analyses of key reactions and kinetic pathways, and kinetic modeling studies were performed for H 2/CO/CO2/CH4/O2/diluent flames spanning a wide range of conditions: equivalence ratios from 0.30 to 2.5, flame temperatures from 1400 to 1800K, pressures from 1 to 25 atm, CO fuel fractions from 0 to 0.9, CO2 dilution fractions up to 0.4, and CH4 fuel fractions from 0 to 0.1. The range of mixture conditions for accurate burning rate determination was extended to include very dilute conditions by improved experimental methodologies that account for the effect of cylindrical chamber confinement on the induced flow field. The experimental data show negative pressure dependence of burning rate at high-pressure, low-flame-temperature conditions for all equivalence ratios and with CO, CO2, and CH 4. Substantial differences are observed between predictions of models currently available in the literature and the experimental data as well as among model predictions themselves -- up to a factor of four at high pressures.;An updated kinetic model was constructed to incorporate recent improvements in rate constant determinations. Particular emphasis was placed on improving the treatment of reactions responsible for HO2 production and consumption, which were found to be important in the flames studied. Major remaining sources of uncertainties, in both the parameters and the assumptions of the kinetic model, were identified that may facilitate further improvements in predicting relevant combustion behavior in the future. Predictions using the updated model adequately reproduce previous validation targets and demonstrate significantly improved agreement with the high-pressure, low-flame-temperature flame speed data taken as part of this study. This improvement in predictive capability for the conditions studied here is of interest to practical syngas applications and other advanced engine technologies.