Revisiting the Kinetics and Thermodynamics of the Low-Temperature Oxidation Pathways of Alkanes: A Case Study of the Three Pentane Isomers

Abstract

This paper describes our developing understanding of low-temperature oxidation kinetics. We have investigated the ignition of the three pentane isomers in a rapid compression machine over a wide range of temperatures and pressures, including conditions of negative temperature coefficient behavior. The pentane isomers are small alkanes, yet have structures that are complex enough to allow for the application of their kinetic and thermochemical rules to larger molecules. Updates to the thermochemistry of the species important in the low-temperature oxidation of hydrocarbons have been made based on a thorough literature review. An evaluation of recent quantum-chemically derived rate coefficients from the literature pertinent to important low-temperature oxidation reaction classes has been performed, and new rate rules are recommended for these classes. Several reaction classes have also been included to determine their importance with regard to simulation results, and we have found that they should be included when developing future chemical kinetic mechanisms. A comparison of the model simulations with pressure-time histories from experiments in a rapid compression machine shows very good agreement for both ignition delay time and pressure rise for both the firstand second-stage ignition events. We show that revisions to both the thermochemistry and the kinetics are required in order to replicate experiments well. A broader validation of the models with ignition delay times from shock tubes and a rapid compression machine is presented in an accompanying paper. The results of this study enhance our understanding of the combustion of straight-and branched-chained alkanes.

Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2-Methylhexane

“…Bugler et al 5 and Zhang et al 6 for the pentane isomers and n-hexane, respectively. Bugler et al 5 also compared rate constants from different studies and provided a recommended set of rate coefficients with uncertainty bounds.…”

“…Bugler et al 5 also compared rate constants from different studies and provided a recommended set of rate coefficients with uncertainty bounds. We will later show how these recommended rate coefficients and their uncertainty bounds can be used for model optimization.…”

“…Both, Miyoshi 12 and Sharma et al 10 calculated the rate coefficients for this reaction class. Bugler et al 5 compared the rate constants of the two studies and investigated in detail the effect of implementing each set on the ignition delay time of pentane isomers. They showed that the use of Sharma's rate coefficients gives very good agreement with experimental ignition delay data, better than when using Miyoshi's rate coefficients.…”

“…The kinetic models for C 5 , C 6 and C 7 alkanes have been recently updated [5][6][7] . Silke et al 7 updated the n-heptane model originally developed by Curran et al 8 .…”

“…In addition to updating the rate coefficients of existing reactions, they added new pathways for RO 2 + OH, RO 2 + HO 2 , cyclic ether formation, and OOQOOH alternative isomerization reactions. Bugler et al 5 revisited the chemical kinetic models of the pentane isomers originally developed by Healy et al 9 . In their work, they investigated the effect of implementing thermodynamic and reaction rate updates [10][11][12][13][14][15] , as well as the addition of alternative OOQOOH isomerization pathways, on the combustion properties of pentane isomers.…”