A shock-tube and laser absorption spectroscopy study of high-temperature ethane/nitric oxide interactions

Accurate kinetic modeling of hydrocarbon–NO x interactions is critical for predicting emissions and reactivity in exhaust gas recirculation (EGR) and reburning-based NO x -reduction systems. Ethane (C 2 H 6 ) is the second-most abundant component in natural gas. Its coupling with NO x is therefore relevant to practical natural gas combustion systems. This study presents the first shock-tube investigation of C 2 H 6 with nitric oxide (NO) in the absence of O 2 , covering fuel-lean to fuel-rich conditions. Experiments were performed near-atmospheric pressure over a temperature range of 1700–2800 K. Time-resolved CO mole fractions were measured using a quantum cascade laser near 4.85 µm. The measurements were used to evaluate recent detailed kinetic mechanisms incorporating NO x and C–N sub-mechanisms. Systematic comparisons of the measured data revealed significant discrepancies between the experiments and predictions of the mechanisms, especially under fuel-lean and low-temperature conditions. CO and OH rate-of-production analyses and pathway analyses show that CO is formed mainly through HCO decomposition at early times and through an HNCO-mediated route at later times, with a smaller direct contribution from C 2 H+NO. Sensitivity analyses identified reactions involving CH 3 +NO as key reactions controlling CO formation. Updating the rate coefficients of CH 3 +NO⇄H 2 CN+OH and CH 3 +NO⇄HCN+H 2 O, using literature values, yielded improved agreement with the measured CO across all equivalence ratios. This study indicates that uncertainty in CH 3 +NO reaction channels can still limit predictive capability for C 2 H 6 /NO interactions. Overall, this work provides the first CO benchmark dataset for the C 2 H 6 /NO system and identifies the CH 3 +NO channels as a limiting source of uncertainty in current mechanisms, supporting future refinement of hydrocarbon/NO x kinetic mechanisms.