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

Abstract

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.

Simulating HCCI Blending Octane Number of Primary Reference Fuel with Ethanol

“…Here, the attempt was to provide a more fundamental explanation of the chemical kinetics of PRF mixtures with ethanol. First, it was noted that the two-stage ignition with negative temperature coefficient (NTC) behavior observed for PRF70 is typical of paraffinic fuels, and is attributed to the competition between various low temperature radical chain branching and chain termination reaction pathways [53,54,55,56,57,58]. The low temperature oxidation pathways ultimately impact the size and nature of the radical pool that is generated, which in turn drives the ignition process.…”

New insights into the low-temperature oxidation of 2-methylhexane

“…Recently, Mohamed et al [13] updated the thermodynamic data and the kinetic reaction mechanism for 2-methylhexane (2MHX) using updated group values and rate rules derived from quantum calculations and experiments. The model was compared against high-and low-temperature 2MHX ignition delay times measured in shock tube and rapid compression machine.…”

“…Besides the well-known species governing auto-ignition, species with four and fiv e oxygen atoms were detected, suggesting the existence of a third O 2 addition process also in 2MHX auto-oxidation. To simulate the experimental observation of the third O 2 addition process, the 2MHX chemical kinetic model from Mohamed et al [13] was extended to include the third O 2 addition to P(OOH) 2 radicals and subsequent reactions of OOP(OOH) 2 radicals. This work describes the kinetics of 2-methylhexane low-temperature auto-oxidation with a focus on C 7 H 14 O 3 species (e.g., keto-hydroperoxdes (KHP) and hydroperoxy cyclic ethers (HPCE)), C 7 H 14 O 2 species (e.g., olefinic hydroperoxides (OHP)), C 7 H 12 O 4 species (e.g., diketo-hydroperoxides (DKHP) and ketohydroperoxy cyclic ethers (KHPCE)), and C 7 H 14 O 5 species (e.g., keto-dihydroperoxides (KDHP) and dihydroperoxy cyclic ethers (DHPCE)).…”

“…This work describes the kinetics of 2-methylhexane low-temperature auto-oxidation with a focus on C 7 H 14 O 3 species (e.g., keto-hydroperoxdes (KHP) and hydroperoxy cyclic ethers (HPCE)), C 7 H 14 O 2 species (e.g., olefinic hydroperoxides (OHP)), C 7 H 12 O 4 species (e.g., diketo-hydroperoxides (DKHP) and ketohydroperoxy cyclic ethers (KHPCE)), and C 7 H 14 O 5 species (e.g., keto-dihydroperoxides (KDHP) and dihydroperoxy cyclic ethers (DHPCE)). Finally, homogenous batch reactor simulations were performed to show that third O 2 addition reactions promote the low-temperature auto-ignition of 2MHX and predict better the ignition properties of 2MHX [13] .…”

Computational Kinetics of Hydroperoxybutylperoxy Isomerizations and Decompositions: A Study of the Effect of Hydrogen Bonding

“…An example is the 5CIPS in 1OOH_2OOj radical as shown in Figure 1. However, recent kinetic studies [17][18][19][20][21][22] showed that alternative isomerization where the peroxy group abstracts a H-atom that is not α to the OOH group (i.e., non α-H isomerization) to form di-hyrdoperoxyalkyl radical P(OOH)2, (e.g. 5AISS and 6AIPS reactions of 1OOH_2OOj in Figure 1) can be a competing pathway, especially for long chain alkanes.…”