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

ABSTRACT

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 NO₂ by HO₂ radicals. The NO-to-NO₂ conversion is enhanced by the production of HO₂ 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 + HO₂ ⇒ OH + NO₂ is followed by OH + C₂H₄ ⇒ C₂H₃ + H₂O and OH + C₂H₆ ⇒ C₂H₅ + H₂O. In the case of ethane, at low temperature, the reaction further proceeds via CH₃ + O₂ ⇒ CH₃O₂; CH₃O₂ + NO ⇒ CH₃O + NO₂; C₂H₅O₂ + NO ⇒ C₂H₅O + NO₂; C₂H₅ + O₂ ⇒ C₂H₄ + HO₂. At higher temperature, the sequence is followed by CH₃O ⇒ CH₂O + H; C₂H₅O ⇒ CH₃CHO + H; C₂H₅O ⇒ CH₃ + CH₂O; CH₂O + OH ⇒ HCO + H₂O; HCO + O₂ ⇒ HO₂ + CO; and H + O₂ ⇒ HO₂. In the case of ethylene, the reaction further proceeds via C₂H₃ + O₂ ⇒ CH₂O + HCO; CH₂O + OH ⇒ HCO + H₂O; HCO + O₂ ⇒ HO₂ + CO; and H + O₂ + M ⇒ HO₂ + M. The main chemical kinetic differences between the two fuels in presence of NO were analyzed.

Keywords:

• ethane
• ethylene
• ignition
• JSR
• kinetic modeling
• NO_x

This research was partially funded through Predit and “Action Concertée Energie” of CNRS-MRNT-DGA (SYNGAZ-GTL-HCCI). G. Dayma thanks CNRS for a post-doc grant.

Notes

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