EXPERIMENTAL STUDY AND DETAILED KINETIC MODELING OF THE MUTUAL SENSITIZATION OF THE OXIDATION OF NITRIC OXIDE, ETHYLENE, AND ETHANE

摘要

New experimental results were obtained for the mutual sensitization of the oxidation of NO and ethane and NO and ethylene in fuel-lean conditions. An atmospheric fused-silica jet-stirred reactor operating over the temperature range 700-1150 K was used. The initial carbon mole fraction was 2500 ppm whereas that of NO varied from 0 to 1200 ppm. Sonic quartz probe sampling followed by on-line Fourier transform infrared analyses and off-line gas chromatography-thermal conductivity detection flame ionization detection analyses were used to measure the concentration profiles of the reactants, stable intermediates, and the final products. A detailed chemical kinetic modeling of the present experiments was performed (147 species, 1085 reversible reactions). An overall good agreement between the present data and modeling was obtained. Furthermore, the proposed model was able to simulate, better than in previous modeling efforts, plug-flow reactor experimental results available in the literature. According to the proposed model, the mutual sensitization of the oxidation of ethane or ethylene and NO proceeds mostly through the conversion of NO to NO_2 by HO_2 radicals. The NO-to-NO_2 conversion is enhanced by the production of HO_2 radicals from the oxidation of the fuel. The production of OH resulting from the oxidation of NO by the hydroperoxy radical promotes the oxidation of the fuel: NO + HO_2 => OH + NO_2 is followed by OH + C_2H_2 => C_2H_3 + H_2O and OH + C_2H_6 => C_2H_5 + H_2O. In the case of ethane, at low temperature, the reaction further proceeds via CH_3 + O_2 => CH_3O_2; CH_3O_2 + NO => CH_3O + NO_2; C_2H_5O_2 + NO => C_2H_5O + NO_2; C_2H_5 + O_2 => C_2H_4 + HO_2. At higher temperature, the sequence is followed by CH_3O => CH_2O + H; C_2H_5O => CH_3CHO + H; C_2H_5O => CH_3 + CH_2O; CH_2O + OH => HCO + H_2O; HCO + O_2 => HO_2 + CO; and H + O_2 => HO_2. In the case of ethylene, the reaction further proceeds via C_2H_3 + O_2 => CH_2O + HCO; CH_2O + OH => HCO + H_2O; HCO + O_2 => HO_2 + CO; and H + O_2 + M => HO_2 + M. The main chemical kinetic differences between the two fuels in presence of NO were analyzed.