Studies of low temperature oxidation of n-pentane with nitric oxide addition in a jet stirred reactor

The low temperature oxidation of n-pentane with nitric oxide (NO) addition has been investigated at 500–800 K in an atmospheric jet stirred reactor (JSR). The molar fraction of NO in the mixture is varied between 0 to 1070 ppm to study its chemical sensitization effect on low temperature oxidation of both fuel lean and rich n-pentane/oxygen mixtures. N-pentane, O₂, CO, CO₂, CH₂O, C₂H₄, CH₃CHO, NO, and NO₂ are quantified simultaneously, in-situ by using an electron impact molecular beam mass spectrometer (MBMS), a micro-gas chromatograph (µ-GC), and a sensitive mid-IR dual-modulation faraday rotation spectrometer (DM-FRS). The experimental results reveal that NO addition delays the onset temperature of low temperature oxidation of n-pentane between 550–650 K, but reduces the negative temperature coefficient (NTC) behavior in the NTC region (650–750 K) and dramatically shifts the onset of high temperature fuel oxidation to an intermediate temperature (750–800 K). A recently developed n-pentane/NO_x model by using Reaction Mechanism Generation (RMG) and a new n-pentane/NO_x model in the present work were used to predict the experimental results. The results show that the three distinct temperature-dependent characteristics of NO sensitized n-pentane oxidation are captured appropriately by these two models at both fuel rich and lean conditions, while the onset temperature of low temperature oxidation is not accurately predicted by these two models. It shows that the RMG model has a better prediction of the onset delay of n-pentane oxidation than Zhao's model, while Zhao's model performs better at NTC and intermediate temperature regions. Besides RO₂ + NO, additional fuel/NO_x reaction pathway, like R + NO₂, RO + NO, and RO + NO₂, and the interconversion reactions among NO, NO₂, and HONO may need to be further studied.