The sensitizing effects of NO2 and NO on methane low temperature oxidation in a jet stirred reactor

Abstract The oxidation of neat methane (CH 4 ) and CH 4 doped with NO 2 or NO in argon has been investigated in a jet-stirred reactor at 107 kPa, temperatures between 650 and 1200 K, with a fixed residence time of 1.5 s, and for different equivalence ratios (Φ), ranging from fuel-lean to fuel-rich conditions. Four different diagnostics have been used: gas chromatography (GC), chemiluminescence NO x analyzer, continuous wave cavity ring-down spectroscopy (cw-CRDS) and Fourier transform infrared spectroscopy (FTIR). In the case of the oxidation of neat methane, the onset temperature for CH 4 oxidation was above 1025 K, while it is shifted to 825 K with the addition of NO 2 or NO, independently of equivalence ratio, indicating that the addition of NO 2 or NO highly promotes CH 4 oxidation. The consumption rate of CH 4 exhibits a similar trend with the presence of both NO 2 and NO. The amount of produced HCN has been quantified and a search for HONO and CH 3 NO 2 species has been attempted. A detailed kinetic mechanism, derived from POLIMI kinetic framework, has been used to interpret the experimental data with a good agreement between experimental data and model predictions. Reaction rate and sensitivity analysis have been conducted to illustrate the kinetic regimes. The fact that the addition of NO or NO 2 seems to have similar effects on promoting CH 4 oxidation can be explained by the fact that both species are involved in a reaction cycle interchanging them and whose result is 2CH 3 + O 2 = 2CH 2 O + 2H. Additionally, the direct participation of NO 2 in the NO 2 + CH 2 O = HONO + HCO reaction has a notable accelerating effect on methane oxidation.