Experimental study and detailed kinetic modeling of the effect of exhaust gas on fuel combustion: mutual sensitization of the oxidation of nitric oxide and methane over extended temperature and pressure ranges

Abstract New experimental results were obtained for the mutual sensitization of the oxidation of NO and methane in a fused silica jet-stirred reactor operating at 1–10 atm, over the temperature range 800–1150 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. Detailed chemical kinetic modeling of the experiments was performed. An overall reasonable agreement between the present data and modeling was obtained, whereas previously published models failed to properly represent these new data. According to the proposed model, the mutual sensitization of the oxidation of methane and NO proceeds through the NO to NO2 conversion by HO2 and CH3O2. The modeling showed that at 1–10 atm, the conversion of NO to NO2 by CH3O2, is more important at low temperatures (800 K) than at higher temperatures (850–900 K), where the reaction of NO with HO2 dominates the production of NO2. The NO to NO2 conversion is enhanced by the production of HO2 and CH3O2 radicals from the oxidation of the fuel. The production of OH resulting from the oxidation of NO promotes the oxidation of the fuel: NO + HO2 ⇄ OH + NO2 is followed by OH + CH4 ⇄ CH3. At low temperature, the reaction further proceeds via CH3 + O2 ⇄ CH3O2, CH3O2 + NO ⇄ CH3O + NO2. At higher temperatures, the production of CH3O involves NO2: CH3 + NO2 ⇄ CH3O. The sequence is followed by CH3O ⇄ CH2O + H, CH2O + OH ⇄ HCO, HCO + O2 ⇄ HO2, and H + O2 ⇄ HO2. ⇄ CH2O + H, CH2O + OH ⇄ HCO, HCO + O2 ⇄ HO2, and H + O2 ⇄ HO2.