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 NO 2 conversion by HO 2 and CH 3O 2. The modeling showed that at 1–10 atm, the conversion of NO to NO 2 by CH 3O 2, is more important at low temperatures (800 K) than at higher temperatures (850–900 K), where the reaction of NO with HO 2 dominates the production of NO 2. The NO to NO 2 conversion is enhanced by the production of HO 2 and CH 3O 2 radicals from the oxidation of the fuel. The production of OH resulting from the oxidation of NO promotes the oxidation of the fuel: NO + HO 2 ⇄ OH + NO 2 is followed by OH + CH 4 ⇄ CH 3. At low temperature, the reaction further proceeds via CH 3 + O 2 ⇄ CH 3O 2, CH 3O 2 + NO ⇄ CH 3O + NO 2. At higher temperatures, the production of CH 3O involves NO 2: CH 3 + NO 2 ⇄ CH 3O. The sequence is followed by CH 3O ⇄ CH 2O + H, CH 2O + OH ⇄ HCO, HCO + O 2 ⇄ HO 2, and H + O 2 ⇄ HO 2. ⇄ CH 2O + H, CH 2O + OH ⇄ HCO, HCO + O 2 ⇄ HO 2, and H + O 2 ⇄ HO 2.