Single Pulse Shock Tube Study of Allyl Radical Recombination

Fridlyand, Aleksandr; Lynch, Patrick T.; Tranter, Robert S.; Brezinsky, Kenneth

doi:10.1021/jp402391n

Cited by 33 publications

(38 citation statements)

References 35 publications

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“…However, this reaction channel can be neglected as the rate constant is about two orders of magnitude lower than the 2-methylallyl radical self-recombination rate constants and does not contribute to fuel reactivity. Rate constants for this reaction are taken from Tranter and co-workers [69] for the allyl radical selfrecombination and have been divided by a factor of 2.3 to match the low temperature ignition delay time measurements, Figure 20. If the iĊ 4 H 7 radical self-recombination reaction were removed from the system, the reactivity would increase significantly in the lower temperature range as shown in Figure 21.…”

Section: Iċ 4 H 7 + Hȯ 2 ↔ Productsmentioning

confidence: 99%

A comprehensive experimental and modeling study of isobutene oxidation

Zhou

O'Connor

et al. 2016

Combustion and Flame

287

185

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Isobutene is an important intermediate in the pyrolysis and oxidation of higher-order branched alkanes, and it is also a component of commercial gasolines. To better understand its combustion characteristics, a series of ignition delay time (IDT) and laminar flame speed (LFS) measurements have been performed. In addition, flow reactor speciation data recorded for the pyrolysis and oxidation of isobutene is also reported. Predictions of an updated kinetic model described herein are compared with each of these data sets, as well as with existing jet-stirred reactor (JSR) species measurements.IDTs of isobutene oxidation were measured in four different shock tubes and in two rapid compression machines (RCMs) under conditions of relevance to practical combustors. The combination of shock tube and RCM data greatly expands the range of available validation data for isobutene oxidation models to pressures of 50 atm and temperatures in the range 666-1715 K. Isobutene flame speeds were measured experimentally at 1 atm and at unburned gas temperatures of 298-398 K over a wide range of equivalence ratios. For the flame speed results, there was good agreement between different facilities and the current model in the fuel-rich region.Ab initio chemical kinetics calculations were carried out to calculate rate constants for important reactions such as H-atom abstraction by hydroxyl and hydroperoxyl radicals and the decomposition of 2-methylallyl radicals.A comprehensive chemical kinetic mechanism has been developed to describe the combustion of isobutene and is validated by comparison to the presently considered experimental measurements. Important reactions, highlighted via flux and sensitivity analyses, include: (a) hydrogen atom abstraction from isobutene by hydroxyl and hydroperoxyl radicals, and molecular oxygen; (b) radical-radical recombination reactions, including 2-methylallyl radical self-recombination, the recombination of 2-methylallyl radicals with hydroperoxyl radicals; and the recombination of 2-methylallyl radicals with methyl radicals; (c) addition reactions, including hydrogen atom and 2 hydroxyl radical addition to isobutene; and (d) 2-methylallyl radical decomposition reactions. The current mechanism accurately predicts the IDT and LFS measurements presented in this study, as well as the JSR and flow reactor speciation data already available in the literature.The differences in low-temperature chemistry between alkanes and alkenes are also highlighted in this work. In normal alkanes, the fuel radical Ṙ adds to molecular oxygen forming alkylperoxyl (RȮ 2 ) radicals followed by isomerization and chain branching reactions which promote low-temperature fuel reactivity. However, in alkenes, because of the relatively shallow well (~20 kcal mol -1 ) for RȮ 2 formation compared to ~35 kcal mol -1 in alkanes, the Ṙ + O 2 ⇌ RȮ 2 equilibrium lies more to the left favoring Ṙ + O 2 rather than RȮ 2 radical stabilization. Based on this work, and related studies of allylic systems, it is apparent that reactivity fo...

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Section: Iċ 4 H 7 + Hȯ 2 ↔ Productsmentioning

confidence: 99%

A comprehensive experimental and modeling study of isobutene oxidation

Zhou

O'Connor

et al. 2016

Combustion and Flame

287

185

View full text Add to dashboard Cite

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“…Resonantly stabilized radicals (RSRs) are typically much less reactive than other common combustion radicals such as OH, H, and O. Consequently, RSRs can accumulate in relatively large concentrations and play important roles in combustion. For instance, allyl radicals have been studied extensively ( [1][2][3] and references therein) and recently Curran et al showed the importance of allyl recombination in simulating propene ignition delay times [4,5]. The related RSR, 2-methylallyl, 2MA, plays a similarly important role in the low temperature ignition of isobutene [6] and is responsible for the effectiveness of tert-butyl ethers in suppressing engine knock [7,8].…”

Section: Introductionmentioning

confidence: 99%

“…Roth et al [9] reported rate coefficients for dissociation of 2,5-dimethyl-1,5-hexadiene (25DM15HD), the reverse of reaction 1 (Note: all reaction numbers refer to Tables 1 and S2), from single pulse shock tube (SPST) experiments over 873-1073 K and obtained k 1 from calculated thermochemical quantities and the equilibrium constant. Bayraceken et al [10] obtained k 1 at 295 K from flash photolysis of 2-methylbut-1-ene (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) Torr). Tsang studied the dissociation of 2,4-dimethylhex-1-ene [11] by SPST (970-1180 K, 1-5 atm) and reported k 3 for dissociation of 2MA.…”

Section: Introductionmentioning

confidence: 99%

“…Previously we have studied the recombination of allyl radicals using a combination of shock tube methods over a broad range of conditions (10-7600 Torr, 650-1700 K) [1,2].The current work presents complementary experimental and ab initio theoretical treatments of the recombination and dissociation of the related RSR 2-methyl allyl. Together these span conditions relevant to low-temperature ignition and master equation modeling provides rate expressions that encompass the low pressure experimental work (c.f.…”

Section: Introductionmentioning

confidence: 99%

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Recombination and dissociation of 2-methyl allyl radicals: Experiment and theory

Tranter

Jasper

Randazzo

et al. 2017

Proceedings of the Combustion Institute

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“…In a previous single pulse shock tube study on the recombination of allyl radicals, 48 it was shown that at the present experimental conditions allyl radicals do not readily dissociate below 1100 K, and preferentially recombined into 1,5-hexadiene. Only above 1100 K will allyl appreciably dissociation to form allene and an H atom.…”

Section: Via Methyl Nonenoate Isomer Model Developmentmentioning

confidence: 56%

Chemical Kinetic Influences of Alkyl Chain Structure on the High Pressure and Temperature Oxidation of a Representative Unsaturated Biodiesel: Methyl Nonenoate

2015

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The high pressure and temperature oxidation of methyl trans-2-nonenoate, methyl trans-3-nonenoate, 1-octene, and trans-2-octene are investigated experimentally to probe the influence of the double bond position on the chemical kinetics of long esters and alkenes. Single pulse shock tube experiments are performed in the ranges p = 3.8-6.2 MPa and T = 850-1500 K, with an average reaction time of 2 ms. Gas chromatographic measurements indicate increased reactivity for trans-2-octene compared to 1-octene, whereas both methyl nonenoate isomers have reactivities similar to that of 1-octene. A difference in the yield of stable intermediates is observed for the octenes when compared to the methyl nonenoates. Chemical kinetic models are developed with the aid of the Reaction Mechanism Generator to interpret the experimental results. The models are created using two different base chemistry submodels to investigate the influence of the foundational chemistry (i.e., C0-C4), whereas Monte Carlo simulations are performed to examine the quality of agreement with the experimental results. Significant uncertainties are found in the chemistry of unsaturated esters with the double bonds located close to the ester groups. This work highlights the importance of the foundational chemistry in predictive chemical kinetics of biodiesel combustion at engine relevant conditions.

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Single Pulse Shock Tube Study of Allyl Radical Recombination

Cited by 33 publications

References 35 publications

A comprehensive experimental and modeling study of isobutene oxidation

A comprehensive experimental and modeling study of isobutene oxidation

Recombination and dissociation of 2-methyl allyl radicals: Experiment and theory

Chemical Kinetic Influences of Alkyl Chain Structure on the High Pressure and Temperature Oxidation of a Representative Unsaturated Biodiesel: Methyl Nonenoate

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