Experimental and detailed kinetic modeling study of hydrogen-enriched natural gas blend oxidation over extended temperature and equivalence ratio ranges

The reduction of CO, CO2, and NOx emissions from combustion in gas turbines can be achieved using hydrogen-enriched fuels operation under very fuel-lean conditions where the emission of NO., is strongly reduced. New experimental results were obtained for the kinetic of oxidation of hydrogen-natural gas mixtures in a fused silica jet-stirred reactor operating at 1 atm, over the temperature range 900-1450 K. Probe sampling followed by on-line FTIR analyses and off-line GC-TCD/FID analyses allowed the measurement of concentration profiles for the reactants, stable intermediates, and final products. Hydrogen addition in variable fractions strongly increases the reactivity of the natural gas blend considered (methane-ethane-propane). The effect is more pronounced in fuel-lean conditions. A detailed kinetic modeling of the present experiments was performed. An overall reasonable agreement between the present data and the modeling was obtained. According to the proposed model, the sensitization of the oxidation of methane by hydrogen proceeds through an increased production of OH radicals by increasing the importance of the reaction H + HO2 double right arrow OH + OH. The increase in hydrogen initial concentration favors the formation of HO2 radicals at low temperature, resulting in increased concentrations of OH and H2O2. The oxidation of hydrogen, when added. and that of methane, ethane, and propane mostly proceed. via reaction with OH. The following sequence of reactions summarizes the mechanism yielding to the observed reactivity increase in hydrogen-enriched mixtures: H + O-2 double right arrow HO2; HO2 + H double right arrow 20H; 2HO(2) double right arrow H2O2; H2O2 double right arrow 20H; and OH + H-2 double right arrow H2O + H followed by reactions of hydrocarbons with OR (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.