Shock-tube measurement and kinetic study of NO₂ promoting-effect on ethane ignition

Ignition delay times have been measured in a high-pressure shock tube for NO₂/C₂H₆/O₂/Ar mixtures at p of 1.2 – 20 atm- and T of 1050 – 1600 K. NO₂ is added to the stoichiometric baseline mixtures (neat ethane mixtures) as 30% and 100% of the ethane concentration by volume. The results indicate that NO₂ significantly promotes the ethane ignition 1) with higher NO₂ addition and 2) at higher pressure and lower temperature. Nevertheless, the NO₂ addition shows ignorable effect on the ethane ignition at lower pressure and higher temperature. A detail kinetic mode is developed against the data measured in this study and is used to perform sensitivity analysis and flux analysis. The kinetic analysis indicates that the interaction between NO₂ and ethane is very strong over the whole conditions investigated in this study. And the promoting-principle of NO₂ on the ethane ignition can be mainly attributed to two aspects: the first one is that reaction (NO + HO2<=>OH + NO₂) converts the stable radicals HO2 into the chain initiating OH radicals; the second one is that the presence of NO₂ accelerates the consumption of these stable fuels (C2H6, CH4, CH2O, CH3) in the system.