Pressure- and temperature-dependent combustion reactions

Golden, David M.; Barker, John R.

doi:10.1016/j.combustflame.2010.08.011

Cited by 41 publications

(46 citation statements)

References 123 publications

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“…In this case, the phenomena of "rotational and vibrational channel switching" take place. 31 Multi-well unimolecular reaction codes 32 then are helpful to the extent that rotational effects can be handled realistically.…”

Section: Discussionmentioning

confidence: 99%

Revisiting falloff curves of thermal unimolecular reactions

Troe

Ushakov

2011

The Journal of Chemical Physics

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Master equations for thermal unimolecular reactions and the reverse thermal recombination reactions are solved for a series of model reaction systems and evaluated with respect to broadening factors. It is shown that weak collision center broadening factors F(cent) (wc) can approximately be related to the collision efficiencies β(c) through a relation F(cent) (wc) ≈ max {β(c) (0.14), 0.64(±0.03)}. In addition, it is investigated to what extent weak collision falloff curves in general can be expressed by the limiting low and high pressure rate coefficients together with central broadening factors F(cent) only. It is shown that there cannot be one "best" analytical expression for broadening factors F(x) as a function of the reduced pressure scale x = k(0)∕k(∞). Instead, modelled falloff curves of various reaction systems, for given k(0), k(∞), and F(cent), fall into a band of about 10% width in F(x). A series of analytical expressions for F(x), from simple symmetric to more elaborate asymmetric broadening factors, are compared and shown to reproduce the band of modelled broadening factors with satisfactory accuracy.

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Section: Discussionmentioning

confidence: 99%

Revisiting falloff curves of thermal unimolecular reactions

Troe

Ushakov

2011

The Journal of Chemical Physics

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“…For multiple-channel and multiple-well systems, more accurate Master Equation (ME) methods have to be envisaged to accurately describe the competition between reaction and collisional stabilisation. Descriptions of these theories can be found in several reviews dealing with RRKM and ME calculations in the field of combustion 167,168 . These approaches constitute the state of the art for the description of pressure dependent multi-well and multi-channel systems.…”

Section: Methods For Improving the Accuracy Of The Thermochemical Amentioning

confidence: 99%

Towards cleaner combustion engines through groundbreaking detailed chemical kinetic models

et al. 2011

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In the context of limiting the environmental impact of transportation, this paper reviews new directions which are being followed in the development of more predictive and more accurate detailed chemical kinetic models for the combustion of fuels. In the first part, the performance of current models, especially in terms of the prediction of pollutant formation, is evaluated. In the next parts, recent methods and ways to improve these models are described. An emphasis is given on the development of detailed models based on elementary reactions, on the production of the related thermochemical and kinetic parameters, and on the experimental techniques available to produce the data necessary to evaluate model predictions under well defined conditions. A IntroductionEven with the expected development of new and cleaner sources of energy, it is still believed that the combustion of liquid fuels will remain the main source of energy for transportation for the next 50 years 1 . It is therefore of the highest importance to limit the environmental impact of using these fuels during this transition period. As traditional fossil fuels are considered to be largely responsible for causing important atmospheric degradations 2 such as global warming 3 , acid rain, and tropospheric ozone increase, an important effort has been made by industry to develop both more efficient types of engines and cleaner types of fuels. A good example is the development of Homogeneous Charge Compression Ignition (HCCI) engines. The HCCI engine is characterised by the fact that the fuel and air are mixed before combustion starts and the mixture auto-ignites as a result of the temperature increase in the compression stroke 4 . This new type of engine has been proposed not only because of its high efficiency compared to that of diesel engines, but also because of its very low emissions compared to gasoline engines with a catalytic converter. With regard to fuels, there is an increasing interest to shift from hydrocarbon fossil fuels to biofuels (particularly bioethanol and biodiesel) 5,6,7,8,9 .While it is especially important to lower the emissions of CO 2 through the use of more efficient powertrains and through an increased biomass derivative content in traditional fuels, the emission reduction of other pollutants should certainly not be neglected. A paper of Wallington et al. 10 describes the parts of automotive engines which could be sources of

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“…Since all required input parameters (three representative frequencies and Lennard Jones parameters for each isomer(well), high-pressure rate constants for isomerization and product forming pathways, and a value for the average energy transferred in collisions ( E all )) can easily be found or estimated, the QRRK/MSC method is suitable for automated mechanism generating algorithms. The second program used in this work to calculate the falloff behavior is MultiWell by Barker et al [24][25][26][27], which implements the stochastic approach outlined by Gillespie [28][29][30]. MultiWell uses either RRKM theory to calculate energy-dependent microcanonical rate constants k(E) for all reaction channels or, alternatively, inverse Laplace transformations of high-pressure rate constants.…”

Section: Pressure-dependent Apparent Rate Constantsmentioning

confidence: 99%

A quantitative kinetic analysis of CO elimination from phenoxy radicals

Carstensen

Dean

2011

Int J of Chemical Kinetics

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Phenoxy radicals are expected to play an important role in the thermal decomposition of lignin. At high enough temperatures, the dissociation to cyclopentadienyl radicals plus carbon monoxide dominates over bimolecular channels. While earlier experimental and theoretical studies agree on the mechanism, the experimental data suggest a substantially lower overall barrier than that found in theoretical studies. To address this discrepancy, we performed electronic structure calculations at the CBS-QB3 level of theory and at a modified version of it to construct the relevant portion of the C 6 H 5 O potential energy surface (PES).The new results are in good agreement with previous studies. We then used the molecular information to calculate thermodynamic properties of the reactants and activated complexes, the high-pressure rate constants, and the pressure dependence. Three different methods were employed for the last step: the quantum version of the Rice-Ramsperger-Kassel/modified strong collision theory approach by Dean (J Phys Chem 1985, 89, 4600-4608), the stochastic treatment by Barker (Int J Chem Kinet 2001, 33, 232-245) using the MultiWell package, and the master equation program Unimol by Gilbert and coworkers. Theory of Unimolecular and Recombination Reactions. Oxford, Blackwell Scientific Publications. All methods predict the experimentally determined phenoxy decomposition rate constant to be in the falloff region. This explains the almost 10 kcal mol −1 difference between reported activation energies and calculated barriers. Both the Lin and Lin (J Phys Chem 1986, 90, 425-431) and Frank et al. (Proc Combust Inst 1994, 25, 833-840) data can be reproduced within the assumed uncertainty limits without any adjustments of the PES. We also report on falloff behavior in the CO elimination from methyl-, hydroxy-, and methoxy-substituted phenoxy radicals in the para position and compare it to that of the unsubstituted phenoxy radical.

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Pressure- and temperature-dependent combustion reactions

Cited by 41 publications

References 123 publications

Revisiting falloff curves of thermal unimolecular reactions

Revisiting falloff curves of thermal unimolecular reactions

Towards cleaner combustion engines through groundbreaking detailed chemical kinetic models

A quantitative kinetic analysis of CO elimination from phenoxy radicals

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