Abstract
The oxidation of 1-butene and i-butene with and without addition of 1000 ppm NO was experimentally and numerically studied primarily at fuel-rich (ϕ = 2.0) conditions under high dilution (96% Ar) in a flow reactor operated at atmospheric pressure in the low temperature range of approximately 600-1200 K. Numerous intermediate species were detected and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). An elementary-step reaction mechanism consisting of 3996 reactions among 682 species, based on literature and this work, was established to describe the reactions and interaction kinetics of the butene isomers with oxygen and nitrogenous components. Model predictions were compared with the experimental results to gain insight into the low- and high-temperature fuel consumption without and with NO addition and thus the respective interaction chemistry. This investigation firstly contributes a consistent set of temperature-dependent concentration profiles for these two butene isomers under conditions relevant for engine exhaust gases. Secondly, the observed oxidation kinetics is significantly altered with the addition of NO. Specifically, NO promotes fuel consumption and introduces for i-butene a low-temperature behavior featuring a negative temperature coefficient (NTC) region. The present model shows reasonable agreement with the experimental results for major products and intermediate species, and it is capable to explain the promoting effect of NO that is initiated by its contribution to the radical pool. Further, it can describe the observed NTC region for the i-butene/NO mixture as a result of the competition of chain propagation and chain terminating reactions that were identified by reaction flow and sensitivity analyses.
Highlights
Alkenes are important intermediates in hydrocarbon combustion and, components of exhaust gases of internal combustion engines [1]
Lean-operated natural gas engines are of special interest, because, on one side, they offer high engine efficiency and less carbon dioxide emissions compared to diesel operated engines, on the other side, their exhaust gas aftertreatment systems suffer from rapid deactivation of the oxidation catalyst for treating the rather significant methane slip [8]
The present investigation has two main aims: First, our study provides a consistent set of detailed measured species profiles for butene isomers, 1-butene and i-butene, at conditions relevant to exhaust gases, i.e. in the appropriate temperature range and in highly diluted mixtures under oxidative conditions
Summary
Alkenes are important intermediates in hydrocarbon combustion and, components of exhaust gases of internal combustion engines [1]. Special attention should be given to the understanding of gas-phase kinetics of both the decomposition chemistry of alkenes and their interaction with nitrogenous species in the low-temperature range and at diluted conditions In this context, the present investigation has two main aims: First, our study provides a consistent set of detailed measured species profiles for butene isomers, 1-butene and i-butene, at conditions relevant to exhaust gases, i.e. in the appropriate temperature range and in highly diluted mixtures under oxidative conditions. The kinetics model was validated against fuel-lean conditions These results were part of a subsequent study in a different reactor setup, and they are only provided in the Supplemental Material (SM1)
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