iso-Octane (2,2,4-trimethylpentane) is a primary reference fuel and an important component of gasoline fuels. Moreover, it is a key component used in surrogates to study the ignition and burning characteristics of gasoline fuels. This paper presents an updated chemical kinetic model for iso-octane combustion. Specifically, the thermodynamic data and reaction kinetics of isooctane have been reassessed based on new thermodynamic group values and recently evaluated

SignificanceHighly oxygenated molecules are involved in autooxidation reactions leading to the formation of secondary organic aerosols (SOAs); they are also critical intermediates in autooxidation processes for liquid hydrogen degradation and the ignition of fuels in advanced combustion systems. However, these reactions are still poorly understood. In this study, we unveil a generalized reaction mechanism involving the autooxidation of peroxy radicals with at least three stages of sequential O2 addition. We elucidate important underlying kinetics and structural characteristics of autooxidation processes used for developing new technologies including those aimed at reducing climatically active SOAs and pollutants from fuel combustion. We show that advances can be made by bridging experimental and theoretical methods used by atmospheric and combustion scientists.

The increasing demand for cleaner combustion and reduced greenhouse gas emissions motivates research on the combustion of hydrocarbon fuels and their surrogates. Accurate detailed chemical kinetic models are an important prerequisite for high fidelity reacting flow simulations capable of improving combustor design and operation. The development of such models for many

Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important to investigate the combustion behavior of real fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracies in certain portions of the models. This study focuses on updating thermodynamic data and the kinetic reaction mechanism for a gasoline surrogate component, 2-methylhexane, 2 based on recently published thermodynamic group values and rate rules derived from quantum calculations and experiments. Alternative pathways for the isomerization of peroxyalkylhydroperoxide (OOQOOH) radicals are also investigated. The effects of these updates are compared against new high-pressure shock tube and rapid compression machine ignition delay measurements. It is shown that rate constant modifications are required to improve agreement between kinetic modeling simulations and experimental data. We further demonstrate the ability to optimize the kinetic model using both manual and automated techniques for rate parameter tunings to improve agreement with the measured ignition delay time data. Finally, additional low temperature chain branching reaction pathways are shown to improve the model's performance.The present approach to model development provides better performance across extended operating conditions while also strengthening the fundamental basis of the model.

CitationAl Rashidi MJ, Mehl M, Pitz WJ, Mohamed S, Sarathy SM (2017) Cyclopentane combustion chemistry. Part I: Mechanism development and computational kinetics. Combustion and Flame 183: 358-371. Available: http://dx. AbstractCycloalkanes are significant constituents of conventional fossil fuels, in which they are one of the main contributors to soot formation, but also significantly influence the ignition characteristics below ~900 K. This paper discusses the development of a detailed high-and low-temperature oxidation mechanism for cyclopentane, which is an important archetypical cycloalkane. The differences between cyclic and non-cyclic alkane chemistry, and thus the inapplicability of acyclic alkane analogies, required the detailed theoretical investigation of the kinetics of important cyclopentane oxidation reactions as part of the mechanism development. The cyclopentyl + O2 reaction was investigated at the UCCSD(T)-F12a/cc-pVTZ-F12//M06-2X/6-311++G(d,p) level of theory in a timedependent master equation framework. Comparisons with analogous cyclohexane or noncyclic alkane reactions are presented. Our study suggests that beyond accurate quantum chemistry the inclusion of pressure dependence and especially that of formally direct kinetics is crucial even at pressures relevant for practical application. KeywordsCyclopentane, detailed mechanism, computational kinetics, pressure-dependent rate constants IntroductionCycloalkanes are important constituents of petroleum-derived liquid fuels. They make up ~40 wt% of diesel [1,2], ~20 wt% of kerosene [3,4], and ~10 to 15 wt% of gasoline [5]. Some studies have shown that at high temperatures, cycloalkanes may contribute to the production of soot by means of de-hydrogenation reactions [6]. Generally, cycloalkanes exhibit less low-temperature reactivity than their non-cyclic counterparts due to the conformational inhibition of the alkylperoxyhydroperoxyalkyl isomerization, an important low-temperature chain branching pathway. Yang et al. [7,8] have shown that in the case of cyclohexane, the suppression of low-temperature isomerization renders the HO2-elimination pathway more important. This leads to higher concentrations of olefins, which reduces reactivity, delays ignition and also promotes soot formation [7]. The ring strain energy changes the oxidation kinetics, particularly for the ring-opening reactions, which also involve significant change in entropy [8].Furthermore, unlike in n-alkanes, methyl substitution in cycloalkanes increases lowtemperature reactivity [9] for reasons that are not well known on the molecular level.Therefore, more detailed kinetic research is needed to better explain the observed trends, and to enable accurate predictive modeling of cycloalkane-containing fuels.Due to their simplicity and abundance, particularly in shale-and oil sand-derived fuels [10], cyclohexane and cyclopentane are often used to represent the naphthenic fraction in surrogate fuels. While models for cyclohexane [11][12][13][14] cover a wide temperature range, the cyclop...