# Chemical kinetic modeling of hydrocarbon combustion (2023)

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• Cited by (1324)
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## Progress in Energy and Combustion Science

Volume 10, Issue 1,

1984

, Pages 1-57

Author links open overlay panelCharles K.Westbrook∗Frederick L.Dryer†

## Abstract

Chemical kinetic modeling of high temperature hydrocarbon oxidation in combustion is reviewed. First, reaction mechanisms for specific fuels are discussed, with emphasis on the hierarchical structure of reaction mechanisms for complex fuels. The concept of a comprehensive mechanism is developed, requiring model validation by comparison with data from a wide range of experimental regimes. Fuels of increasing complexity from hydrogen to n-butane are described in detail, and further extensions of the general approach to other fuels are discussed.

(Video) Chemical Kinetic Modeling for Combustion, Curran, Day 3, Part 1

Kinetic modification to fuel oxidation kinetics is considered, including both inhibition and promotion of combustion. Simplified kinetic models are then described by comparing their features with those of detailed kinetic models. Finally, application of kinetic models to study real combustions systems are presented, beginning with purely kinetic-thermodynamic applications, in which transport effects such as diffusion of heat and mass can be neglected, such as shock tubes, detonations, plug flow reactors, and stirred reactors. Laminar flames and the coupling between diffusive transport and chemical kinetics are then described, together with applications of laminar flame models to practical combustion problems.

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(Video) Chemical Kinetic Modeling for Combustion, Curran, Day 1, Part 1

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• ## Cited by (1324)

• Impact of PODE<inf>3</inf> on soot oxidation reactivity at different stages in n-heptane/toluene diffusion flames

2023, Fuel

PODE3, with the molecular formula of CH3O(CH2O)3CH3, is considered a highly competitive alternative fuel due to the absence of CC bond and its high oxygen content, and have been shown to significantly reduce soot emission when applied as a diesel fuel additive. However, the effect of PODE3 addition on the oxidation reactivity of soot generated in the flame remains unclear which is of great importance for the optimal design of the post-treatment devices during its application. In this work, the impact of PODE3 (0%, 10%, and 20% by volumetric fraction) addition on the oxidation reactivity of soot at different maturity and oxidation degrees in n-heptane/toluene co-flow diffusion flames was specially investigated combining information on thermogravimetric analysis, high-resolution transmission electron microscope, and Raman spectroscopy. Results showed that PODE3 substitution significantly shrank soot generation region, and increased the flame temperatures before height above burner (HAB)<45mm. The addition of PODE3 improved the soot oxidation reactivity, which had a strong ability to hinder the growth of the microcrystalline carbon layers and resulted in a high content of amorphous carbon in soot particles. Specifically, it had more significant impacts on the soot in the oxidation stage than the surface growth stage. These can be explained that with PODE3 addition, on the one hand, the “reliable carbon atom” for soot formation is significantly reduced and the amount of oxidizing species is increased, resulting in a smaller particle size and a higher content of disordered and amorphous carbon in soot particles. On the other hand, the flame temperatures increased where HAB<45mm, which would promote the soot formation reactions. The combined effects of these factors make PODE3 have more significant inhibitory impacts in reactivity of soot sampled at oxidation stage than that at surface growth stage. Therefore, the impact of PODE3 addition on soot nanostructures and oxidation reactivity is not only reflected in its chemical effect but also in temperature effect.

• Optimization of a gas turbine model combustor due to variations in geometrical characteristics of stabilizing air jets

2022, Applied Thermal Engineering

The main purpose of this paper is to optimize the objective parameters in a gas turbine model combustor. These parameters include ${\mathrm{N}\mathrm{O}}_{\mathrm{x}}$ and $\mathrm{C}\mathrm{O}$ pollutants as well as pattern factor. $\mathrm{C}\mathrm{O}$ is based on a maximum produced value in the model combustor. To optimize the objective parameters, the input characteristics (such as diameter, angle, and position of the stabilizing air jets) are varied. Simulation of the combustion process comprises turbulent flow, combustion, radiative heat transfer, and fuel injection modeling. The models employed for this simulation, based on RANS approach, are realizable $\phantom{\rule{0ex}{0ex}}\mathrm{k}-\mathrm{\epsilon }$ for flow turbulence, steady flamelet model for combustion, discrete ordinates model for radiative heat transfer, and Eulerian-Lagrangian approach for fuel injection. A diesel fuel (C10H22) is used in the model combustor and ${\mathrm{N}\mathrm{O}}_{\mathrm{x}}$ modeling is conducted via post-processing. Artificial neural network is applied to gain an approximated trained function based on results and input geometrical characteristics. Data for training the artificial neural network is generated by means of design of experiments. For finding the optimum point, genetic algorithm is utilized. The obtained neural network function is applied to genetic algorithm so as to extract the optimum points. Since there is more than one objective parameter a set of optimum points is obtained which is called the Pareto front. Using multiple-criteria decision making method (LINMAP model), the final optimum point is achieved. The optimum point shows that the amounts of ${\mathrm{N}\mathrm{O}}_{\mathrm{x}}$, $\mathrm{C}\mathrm{O}$, and pattern factor are improved by up to 11.31%, 2.88%, and 21.07%, respectively. The value of soot which is not a part of optimization is also improved by up to 24.46%.

• Further insights into the core mechanism of H<inf>2</inf>/CO/NO<inf>x</inf> reaction system

2022, Combustion and Flame

The core H2/CO/NOx mechanism is important in understanding the mechanism of NOx formation during combustion as it forms the base model in developing kinetic models of larger hydrocarbons/NOx systems. Recently, the Goldsmith group at Brown University performed high-level ab-initio calculations of the chemistry of HONO and HNO2 and proposed that the thermal rate constant of isomerization of HONO to HNO2 is orders of magnitude lower than that used in all previous models. This discrepancy may lead to a deviation in understanding the formation mechanism of NOx. With this in mind, coupling with the latest rate constants obtained by experimental measurements and high-level quantum chemistry calculations, the H2/CO/NOx model was circularly updated and re-verified against multi-type datasets over a wide range of initial conditions and experimental devices. The proposed model (XJTUNO-2021) can accurately reproduce almost all of the fundamental combustion data including 156 shock tube datasets, 87 JSR datasets, 114 flow reactor datasets and six laminar flame speed datasets in the literature from 1959 to 2021. Moreover, this study clarifies the shortcomings of the Zhang mechanism of CO/NOx systems. Finally, the updated model has been used to simulate the formation of NO at practical gas-turbine conditions to give more kinetically information of NO control technologies.

• Optimized two-step (OTS) chemistry model for the description of partially premixed combustion

2022, Combustion and Flame

Once properly optimized, single-step chemistry models are able to recover essential characteristics of flames such as burned gases temperature, flame propagation velocity and thickness. Ignition delay values can be reproduced as well. However, an improved description of either the premixed flame inner structure or the ignition process requires the consideration of the multi-step nature of chemical kinetics. Indeed, single-step chemistry models can neither describe properly the internal structure of laminar premixed flames nor the development of ignition processes. These limitations arise because single-step chemistry does not take into account intermediate species, the importance of which is essential. Thus, the present work is aimed at extending the recently-proposed optimized single-step (OSS) framework to multi-step chemistry. To this purpose an unbranched chain reaction with only two consecutive steps relevant to chain initiation and chain termination is considered. The corresponding kinetics model does involve two fictive species, the characteristics of which are optimized together with the two-step chemical scheme parameters,e.g.,pre-exponential factors and activation energies. One of this fictive species is relevant to combustion products while the other represents the whole pool of radicals. The chemistry optimization procedure makes use of a well-defined in-house genetic algorithm and the resulting optimized two-step (OTS) model is assessed through comparisons made with data obtained from detailed chemistry computations used as reference. For similar (and even lower) CPU costs, the computations performed with the OTS model put into evidence significant improvements compared to the results obtained with the OSS description.

• Ethanol as a renewable biofuel: Combustion characteristics and application in engines

2022, Energy

The present review article aims to study different aspects involving ethanol combustion and utilization. The review deals with the production and sustainability of corn-based and sugarcane-based ethanol as a starting point to present ethanol as a renewable and sustainable biofuel. The second step is to present the current understanding of ethanol combustion, regarding the application of thermodynamic theory and detailed chemical kinetic mechanisms to model the combustion processes. The utilization of ethanol implies consideration of safety parameters related to its combustion. Therefore, a section was dedicated to discussing the flammability limits and detonability limits of ethanol and their experimental determination. The application of gasoline-ethanol blends in spark ignition engines and diesel-ethanol blends in compression ignition engines is also addressed. New techniques (as dual injection) are being considered to improve the combustion efficiency. Also, the use of biodiesel in diesel-ethanol-biodiesel blends has shown to be a promising possibility. The greenhouse gas emissions obtained in different experimental works with internal combustion engines running on different fuel blends involving ethanol were also reviewed. Ethanol potentially increases the thermal efficiency of internal combustion engines and reduces the NOx emissions. Finally, the possibility of integrating internal combustion engines and ethanol fuel cells is also considered.

• The dimensional design of a laboratory-scale fluidized bed gasifier using machine learning based on a kinetic method

2022, Energy Conversion and Management

Gasification provides various environmental and technological advantages, and the efficiency of the gasification system is affected by several factors, including the kind of fuel and gasification agent used, the gasifier's length and diameter, the operating pressure and temperature, etc. Experimental optimization approaches are more realistic, but they are time demanding; also, a reactor operating at high temperatures and pressures could be dangerous and expensive. Thus, researchers use a variety of modeling techniques, including the process simulators. Additionally, artificial neural network (ANN) as a machine learning approach, which is one of the process modeling methods, is a remarkable approach, and several papers have been published in which it has been utilized in combination with other modeling techniques. On the other hand, a combined process simulator/ANN model that considers gasifier design/operational parameters for the kinetic modeling of gasification process has not been reported.

In this study, after kinetic modeling and validation of seven different circulating fluidized gasifiers using Aspen Plus, parametric studies were performed. Parametric analysis was used to examine the impacts of gasifier diameter, length, gasifier temperature, air/fuel ratio, and fuel type, and a dataset was created for ANN training. The syngas composition and thermal value were predicted using the ANN model. Therefore, a model was developed that takes into consideration both design and operating variables. The investigations revealed that heterogeneous reactions were the most critical factor in defining syngas characteristics. Although design factors have a considerable impact on syngas characteristics, the gasifier temperature is a key factor in the whole process. Furthermore, the ANN model estimates syngas specifications with great accuracy (R2>0.99 and MAPE<3%) based on fuel attributes and gasifier design/operating parameters. Hence, ANN models can be used to analyze the effectiveness of systems including a complex combination of reactions and thermochemical processes.

View all citing articles on Scopus
(Video) Chemical Kinetic Modeling for Combustion, Curran, Day 5, Part 1

## Recommended articles (6)

• Research article

Pressure-dependent kinetics on the C4H7 potential energy surface and its effect on combustion model predictions

Combustion and Flame, Volume 181, 2017, pp. 100-109

(Video) Chemical Kinetic Modeling for Combustion, Curran, Day 1, Part 2

Butene (C4H8), the smallest alkene possessing both branched and straight-chain isomers, is usually an important intermediate with relatively high concentration in the combustion of hydrocarbons and oxygenated fuels. In the present study, the kinetics of thermal isomerization, decomposition and chemical activation reactions of three typical butenyl isomers, i.e. nC4H7 (CH2=CHCH2ĊH2), saxC4H7 (CH2=CHĊHCH3) and iC4H7 (CH2=C(CH3)ĊH2), were systematically investigated by theoretical calculations. High-level ab initio calculations coupled with the RRKM/master equation method were used to compute the temperature and pressure dependent rate coefficients. The results show that the existence of vinylic CC bond in iC4H7 largely impedes its decomposition rate. The transformation from iC4H7 to straight-chain C4H7 is kinetically unfavorable due to the high strain energy of the 3-membered ring structure of the isomerization transition state. Furthermore, the calculated rate coefficients were incorporated into USC Mech II and Aramco Mech 2.0 to examine the impact of our computed pressure-dependent kinetics on model predictions. Although the simulation results demonstrate limited improvement on ignition delay time and laminar flame speed of butene, substantial changes are observed for the mole fractions of important intermediate species, e.g., allene and 1,3-butediene, in butene pyrolysis. Modified Arrhenius representations of the calculated rate constants are given and should be used in combustion modeling.

• Research article

Uncertainty of the rate parameters of several important elementary reactions of the H2 and syngas combustion systems

Combustion and Flame, Volume 162, Issue 5, 2015, pp. 2059-2076

Re-evaluation of the temperature-dependent uncertainty parameter f(T) of elementary reactions is proposed by considering all available direct measurements and theoretical calculations. A procedure is presented for making f(T) consistent with the form of the recommended Arrhenius expression. The corresponding uncertainty domain of the transformed Arrhenius parameters (ln A, n, E/R) is convex and centrally symmetric around the mean parameter set. The f(T) function can be stored efficiently using the covariance matrix of the transformed Arrhenius parameters. The calculation of the uncertainty of a backward rate coefficient from the uncertainty of the forward rate coefficient and thermodynamic data is discussed. For many rate coefficients, a large number of experimental and theoretical determinations are available, and a normal distribution can be assumed for the uncertainty of ln k. If little information is available for the rate coefficient, equal probability of the transformed Arrhenius parameters within their domain of uncertainty (i.e. uniform distribution) can be assumed. Algorithms are provided for sampling the transformed Arrhenius parameters with either normal or uniform distributions. A suite of computer codes is presented that allows the straightforward application of these methods. For 22 important elementary reactions of the H2 and syngas (wet CO) combustion systems, the Arrhenius parameters and 3rd body collision efficiencies were collected from experimental, theoretical and review publications. For each elementary reaction, kmin and kmax limits were determined at several temperatures within a defined range of temperature. These rate coefficient limits were used to obtain a consistent uncertainty function f(T) and to calculate the covariance matrix of the transformed Arrhenius parameters.

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Algorithmic determination of the mechanism through which H2O-dilution affects autoignition dynamics and NO formation in CH4/air mixtures

Fuel, Volume 183, 2016, pp. 90-98

The Computational Singular Perturbation (CSP) algorithm is employed in order to determine how ${\text{H}}_{2}\text{O}$-dilution influences ignition delay and chemical paths that generate NO during isochoric homogenous lean ${\text{CH}}_{4}$/air autoignition. Regarding the ignition delay, it is shown that ${\text{H}}_{2}\text{O}$-dilution enhances reactivity, mainly due to the increased OH production throughout the explosive stage via reaction ${\text{H}}_{2}{\text{O}}_{2}\left(+{\text{H}}_{2}\text{O}\right)\to \text{OH}+\text{OH}\left(+{\text{H}}_{2}\text{O}\right)$. With regard to NO generation, the relative importance of thermal and chemical effects are examined and it is concluded that both are important. The thermal effects result in a lower temperature at the end of the explosive stage, while the most notable chemical effect is the lower level of O after this stage, mainly due to the effect of ${\text{H}}_{2}\text{O}$-dilution on the equilibrium of the reaction $\text{O}+{\text{H}}_{2}\text{O}↔\text{OH}+\text{OH}$. The depletion of O, together with the thermal effect, causes a substantial decrease in final NO generation.

• Research article

The oxidation of 2-butene: A high pressure ignition delay, kinetic modeling study and reactivity comparison with isobutene and 1-butene

Proceedings of the Combustion Institute, Volume 36, Issue 1, 2017, pp. 403-411

Butenes are intermediates ubiquitously formed by decomposition and oxidation of larger hydrocarbons (e.g. alkanes) or alcohols present in conventional or reformulated fuels. In this study, a series of novel ignition delay time (IDT) experiments of trans-2-butene were performed in a high-pressure shock tube (HPST) and in a rapid compression machine (RCM) under conditions of relevance to practical combustors. This is the first IDT data of trans-2-butene taken at engine relevant conditions, and the combination of HPST and RCM results greatly expands the range of data available for the oxidation of trans-2-butene to higher pressures (10–50atm), lower temperatures (670–1350K) and a wide range of equivalence ratios (0.5–2.0). A comprehensive chemical kinetic mechanism has simultaneously been developed to describe the combustion of trans-2-butene. It has been validated using the IDT data measured here in addition to a large variety of literature data: jet-stirred reactor (JSR) speciation data, premixed flame speciation data, flow reactor speciation data and laminar flame speed data. Moreover, the reactivity of trans-2-butene is compared to that of the other two isomers, 1-butene and isobutene, and these comparisons are discussed. Important reactions are highlighted via flux and sensitivity analyses and help explain the differences in reactivity among the butene isomers.

• Research article

Direct measurements of channel specific rate constants in OH + C3H8 illuminates prompt dissociations of propyl radicals

Proceedings of the Combustion Institute, Volume 37, Issue 1, 2019, pp. 231-238

OH + molecules are an important class of reactions in combustion and atmospheric chemistry. Consequently, numerous studies have measured rate constants for these processes over an extended temperature range. A large majority of these experimental studies have utilized the decay of [OH] profiles (monitored either by absorption or laser-induced fluorescence) to obtain total rate constants. However, there are limited direct measurements of channel specific rate constants in this important class of reactions, particularly at combustion relevant temperatures. In the present experiments, we have directly measured site-specific rate constants for abstraction of the secondary CH bond in OH + C3H8 at high temperatures. Atomic resonance absorption spectrometry (ARAS) was used to monitor the formation of H-atoms from shock-heated mixtures of tert-butylhydroperoxide and C3H8 at high temperatures. Simulations for the experimental H-atom profiles are sensitive only to abstraction of the secondary CH bond leading to unambiguous measurements of the rate constants for this reaction. Over the T-range, 921 K < T < 1146 K, rate constants from the present experiments for OH + C3H8 → H2O + i-C3H7 can be represented by the Arrhenius expression,

$k=\left(3.935±1.387\right)×{10}^{-11}\phantom{\rule{0ex}{0ex}}\text{exp}\left(-1681±362\phantom{\rule{0ex}{0ex}}\mathrm{K}/T\right)\mathrm{c}{\mathrm{m}}^{3}\text{molecul}{\mathrm{e}}^{-1}{\mathrm{s}}^{-1}$

Simulations of the lower temperature data (T < 1000 K) indicate that the H-atom profiles are also influenced to a minor extent by the thermal dissociation of iso-propyl, i-C3H7 → H + C3H6, at short time-scales. Direct dynamics calculations were performed to examine in greater detail the potential role of prompt dissociations of i-C3H7 and n-C3H7 (formed from the title reaction) in interpreting the lower temperature (< 1000 K) data from the present work. These simulations suggest that prompt dissociation of propyl radicals does not influence the present experimental observations but has a minor influence on higher temperature combustion simulations.

• Research article

Investigation on the oxidation chemistry of methanol in laminar premixed flames

Combustion and Flame, Volume 180, 2017, pp. 20-31

In this work, oxidation chemistry of methanol was investigated in laminar premixed flames. Laminar burning velocities of methanol/air mixtures at 423K and 1–10atm were measured in a spherical combustion vessel, extending the range of equivalence ratio up to 2.1. A stoichiometric premixed flat flame of methanol/O2/Ar at 0.04atm was also conducted using synchrotron VUV photoionization mass spectrometry (SVUV-PIMS) to obtain more detailed kinetic information. Particularly, fuel-derived radicals including methoxy radical and hydroxymethyl radical were observed, while formaldehyde (CH2O) and formic acid (HOCHO) were identified as the abundantly produced intermediates in methanol flame. A methanol model was developed and validated against the experimental data obtained in this work, as well as in literature. In the predictions of laminar burning velocities, HO2 radical plays an important role under very rich conditions. Besides, the measurement of formaldehyde and formic acid in methanol flame is helpful to constrain the rate constant of CH2OH+O2=CH2O+HO2, which presents large uncertainties at high temperatures.

(Video) Chemical Kinetic Modeling for Combustion, Curran, Day 4, Part 2

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