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/NOx model and Zhao's n-pentane/NOx 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.