Experimental and modeling study of the mutual oxidation of N-pentane and nitrogen dioxide at low and high temperatures in a jet stirred reactor

The mutual oxidation of n-pentane and NO₂ at 500–1000 K has been studied at equivalence ratios of 0.5 and 1.33 by using an atmospheric-pressure jet stirred reactor (JSR). N-pentane, O₂, NO, NO₂, CO, CO₂, CH₂O, C₂H₄, and CH₃CHO are simultaneously quantified, in-situ by using an electron-impact molecular beam mass spectrometer (EI-MBMS), a micro-gas chromatograph (μ-GC), and a mid-IR dual-modulation faraday rotation spectrometer (DM-FRS). Both fuel lean and rich experiments show that, in 550–650 K, NO₂ addition inhibits low temperature oxidation. With an increase of temperature to the negative temperature coefficient (NTC) region (650–750 K), NO₂ addition weakens the NTC behavior. In 750–1000 K, high temperature oxidation is accelerated with NO₂ addition and shifted to lower temperature. Two kinetic models, a newly developed RMG n-pentane/NO_x model and Zhao's n-pentane/NO_x model (Zhao et al., 2018, Submitted) were validated against experimental data. Both models were able to capture the temperature-dependent NO₂ sensitization characteristics successfully. The results show that although NO₂ addition in n-pentane has similar effects to NO at many conditions due to fast NO and NO₂ interconversion at higher temperature, it affects low temperature oxidation somewhat differently. When NO₂/NO interconversion is slow, NO₂ is relatively inert while NO can strongly promote or inhibit oxidation.