Publications
141 results found
Lindstedt RP, Maurice LQ, 2000, Detailed chemical-kinetic model for aviation fuels, Pages: 187-195, ISSN: 0748-4658
The introduction of detailed chemical reaction mechanisms for aviation fuels into complex multidimensional fluid dynamics problems is not practical at the present time. Simplified reaction mechanisms that have been thoroughly evaluated must be developed to address specific issues arising in realistic combustor configurations. The latter should be firmly based on detailed mechanisms carefully evaluated against a wide range of experimental data. A detailed kinetic mechanism for hydrocarbon combustion is formulated to address the gas-phase chemistry of endothermic and conventional aviation fuels. Reaction paths are analysed for n-decane and kerosene premixed flames, and the ability of the mechanism to predict various premixed flame features is assessed by comparison with experimental species profiles. Finally, the level of success achieved by the present kinetic model in the context of practical problems is discussed.
Lindstedt RP, Skevis G, 2000, Molecular growth and oxygenated species formation in laminar ethylene flames, Proceedings of the Combustion Institute, Vol: 28, Pages: 1801-1807, ISSN: 1540-7489
Ethylene constitutes a key intermediate in the oxidation of practical hydrocarbon fuels. Past studies of ethylene oxidation in shock tubes, flow/stirred reactors, and flames have provided an understanding of several key aspects of the fuel oxidation chemistry. However, the current trend toward leaner premixed combustion in practical devices results in significant changes in the combustion regime, and studies under fuel-lean flame conditions have become essential. The changes in the main reaction channels are significant, and the chemistry of oxygenated species comes to the fore. The present work compares the main reaction paths in fuel-rich and fuel-lean ethylene flames, with particular emphasis on the relative importance of addition, abstraction, and isomerization paths in the context of the formation of oxygenated and aromatic species. It is shown that in the fuel-lean flame, ethylene is mainly consumed by addition reactions, while in the rich flame environment, abstraction reactions leading to vinyl radical formation dominate. The balancing of the destruction chemistry of the latter and the importance of the rate and product distribution of the molecular oxygen attack are discussed in detail. It is noted that the channel C2H4 + O = CH2CHO + H is the dominant route to vinoxy under lean flame conditions, and the present work supports the acetyl channel (CH2CHO → CH3CO → CH3 + CO) for vinoxy destruction at elevated temperatures. Potential benzene formation paths are assessed, and it is concluded that vinyl radical addition to vinylacetylene and propargyl radical recombination constitute the major benzene formation paths in rich ethylene flames. The present work thus further emphasises the need to consider multiple benzene formation channels.
Lindstedt RP, Váos EM, 2000, Modeling of mixing processes in non-isothermal and combusting flows, 8th European Turbulence Conference, Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 493-496
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- Citations: 3
Lindstedt RP, Skevis G, 2000, Molecular growth and oxygenated species formation in laminar ethylene flames, PROCEEDINGS OF THE COMBUSTION INSTITUTE, Vol: 28, Pages: 1801-1807, ISSN: 1540-7489
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- Citations: 27
Lindstedt RP, 2000, The modelling of direct chemical kinetic effects in turbulent flames, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING, Vol: 214, Pages: 177-189, ISSN: 0954-4100
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- Citations: 6
Lindstedt RP, Vaos EM, 2000, Modelling of mixing processes in non-isothermal and combusting flows, Advances in Turbulence, Pages: 493-496, ISBN: 9788489925656
Lindstedt RP, Váos EM, 1999, Modeling of premixed turbulent flames with second moment methods, Combustion and Flame, Vol: 116, Pages: 461-485, ISSN: 0010-2180
Turbulent premixed flames feature complex interactions between turbulent transport of scalars and chemical reaction as well as a strong coupling between velocity and scalar turbulence. The present work concerns the modeling of such flames at the second moment closure level and mainly focuses on the critical role of pressure redistribution/scrambling. It is shown that the common and exclusive practice of past work in this area, which involves a density weighted rewriting of models derived on a constant density basis, is insufficient. To resolve this issue a class of model extensions is proposed to account for variable density effects. The accuracy of the proposed approach is illustrated by consideration of incompressible premixed turbulent flames in the laminar flamelet regime of combustion. However, the proposed approach is general and does not preclude the consideration of other combustion regimes or the use of sophisticated closures for reaction related terms. The full closure is here applied to the simulation of transient one- dimensional flames and fully two-dimensional flames stabilized in counterflow geometries. The obtained level of agreement with experimental data proves most encouraging and constitutes a significant advance over past modeling efforts.
Pickenacker VO, Trimis D, Brenner G, et al., 1999, Numerical studies of airbag gas generators with organic propellants, ATZ automobiltechnische zeitschrift, Vol: 101, Pages: 9-11, ISSN: 0001-2785
Lindstedt RP, Sakthitharan V, 1999, Parallel processing and direct simulation of transient premixed laminar flames with detailed chemical kinetics, High Performance Computing, Editors: Allen, Publisher: Kluwer, ISBN: 9780306460340
Maurice LQ, Blust JW, Leung KM, et al., 1999, Emissions from combustion of hydrocarbons in a well stirred reactor, 37th AIAA Aerospace Sciences Meeting and Exhibit (Nevada)
Lindstedt P, Leung K, 1998, Molecular growth processes in the gas phase, Publisher: AMER CHEMICAL SOC, Pages: U615-U615, ISSN: 0065-7727
Lindstedt RP, Sakthitharan V, 1998, Time resolved velocity and turbulence measurements in turbulent gaseous explosions, COMBUSTION AND FLAME, Vol: 114, Pages: 469-483, ISSN: 0010-2180
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- Citations: 25
Lindstedt RP, Váos EM, 1998, Second moment modeling of premixed turbulent flames stabilized in impinging jet geometries, Symposium (International) on Combustion, Vol: 27, Pages: 957-962, ISSN: 0082-0784
The present work comprises a computational study of premixed turbulent flames stabilized in a stagnation point flow geometry. Past work in this area has focused mainly on the closure of the mean reaction rate and exclusively featured gradient diffusion-type approximations for the turbulent transport of momentum and scalars. The shortcomings of gradient diffusion-based closures in such flows are well established, and turbulent transport has been shown to exert a significant influence on the evolution of global and local flame properties. Thus, the present study comprises a full second moment closure for both velocity and scalar turbulent transport and includes extended variable density forms for the pressure redistribution, pressure scrambling, and dissipation generation terms. The proposed extensions are general and independent of the combustion regime considered. The accuracy of the approach is illustrated by the application of the resulting equations to the simulation of a stoichiometric ethylene and air premixed turbulent flame stabilized in an impinging jet geometry. Comparisons with available experimental data are highly encouraging and reveal excellent agreement for predictions of both mean and turbulent quantities. Furthermore, the generality and superiority of second moment methods over gradient diffusion closures is clearly established. The present study has fundamental implications for the development of turbulent transport and reaction rate models.
Sick V, Hildenbrand F, Lindstedt P, 1998, Quantitative laser-based measurements and detailed chemical kinetic modeling of nitric oxide concentrations in methane-air counterflow diffusion flames, Symposium (International) on Combustion, Vol: 27, Pages: 1401-1409, ISSN: 0082-0784
The formation and destruction of nitric oxide in diffusion flames remains a topic of particular relevance to practical applications. In the present work, the chemistry of NO in atmospheric methane-air counterflow diffusion flames is investigated by quantitative laser spectroscopic measurements and detailed chemical kinetic modeling. Highly resolved spatial NO concentration profiles have been obtained using laser-induced fluorescence (LIF), and the influence of temperature and collisions on the quantitative interpretation of LIF signals is described. Experimental nitric oxide profiles obtained in pure CH 4-air flames and CH4-air flames seeded with NO and NH 3 are presented. Comparisons are made with computations featuring a detailed chemical kinetic mechanism with 74 species and 506 reactions. It is shown that acceptable agreement is obtained, and the main areas of uncertainty are outlined. Thus, three current recommendations (GRI Mech. 2.11, Dean et al., and Lindackers et al.) for the "prompt" NO formation channel CH + N2 are assessed. In apparent agreement with the theoretical study of Miller and Walch, the present work tentatively supports the determination of Dean et al., and it is suggested that the computer-optimized rate used in GRI-Mech. 2.11 is significantly (∼250%) too slow. It is further shown that methane diffusion flames differ from their premixed counterparts and that reaction channels such as CH with H2O and NO with HCCO exert a primary influence on computed results.
Lindstedt P, 1998, Modeling of the chemical complexities of flames, Symposium (International) on Combustion, Vol: 27, Pages: 269-285, ISSN: 0082-0784
One of the notable successes of combustion research is the increasing ability to model detailed flame structures of practical fuels accurately. The progress made has to a significant extent been motivated by socioeconomic and political pressures to increase burning efficiency and to reduce environmental impact. Combustion technology influences practically every aspect of life, and increasingly a comprehensive knowledge of flame chemistry is a prerequisite for the ability to design effective fuels and combustion devices. Furthermore, the introduction of chemistry into design computations currently requires the application of rigorous simplification procedures to reduce the number of independent scalars. The ultimate goal is automatic mechanism generation/reduction enabling the direct incorporation of combustion chemistry into design procedures. At present, detailed kinetic mechanisms are in many cases sufficiently mature to aid designers in solving chemistry-related problems from a fundamental scientific perspective. However, progress is required for higher hydrocarbons, which account for around two-thirds of the total power generation worldwide. These practical fuels typically feature complex mixtures of alkanes and aromatics with alkenes and alkynes playing a key role in the overall oxidation chemistry. Based on a review of the progress made in the understanding of the chemical complexities of such flames, it is argued that characterization of the high-temperature combustion chemistry into traditional reaction classes suchas abstraction, addition, and isomerization provides useful consistency checks and constitutes a step toward automatic mechanism generation. The relative importance of such reaction classes is shown to depend largely on the specific fuel and burning conditions. Progress in this truly multidisciplinary area remains dependent upon continued advances in chemical and mathematical modeling, computing power, procurement of kinetic data, and the developm
Juchmann W, Latzel H, Shin DI, et al., 1998, Absolute radical concentration measurements and modeling of low-pressure CH<inf>4</inf>/O<inf>2</inf>/NO flames, Symposium (International) on Combustion, Vol: 27, Pages: 469-476, ISSN: 0082-0784
An experimental and theoretical investigation of CH and CN radical formation and destruction in a low-pressure 13.3-hPa (10 Torr) premixed stoichiometric CH4/O2 flame seeded with NO is presented. Relative concentration profiles of CH and CN are measured by linear unsaturated laser-induced fluorescence(LIF). An absolute calibration of the relative profiles is obtained by Rayleigh scattering. A computational study is performed to identify key uncertainties in the formation and destruction chemistry of the CH and CN radicals. It is shown that the reaction of the CH radical with molecular oxygen is of particular importance in the present flame. Prevailing uncertainties in the reactions of 3CH2 with hydrogen atoms and molecular oxygen are also discussed. The present quantitative measurements of the CN radical also indicate that further attention should be given to the formation and oxidation chemistry of HCN. Nevertheless, computational results are encouraging and reasonable agreement is obtained for both the CH and CN radicals. It is further shown that the effects on CH concentration levels of introducing NO dopants may be reproduced. Comparisons of absolute concentration profiles of CH3, OH, and CH radicals as well as NO are also made with computed results obtained using GRI Mech. 2.11 and a reaction mechanism developed by Warnatz. The computations highlight significant differences in reaction paths and rate selection. The major areas of uncertainty are outlined and tentative recommendations are made in relation to the key reaction paths.
Hůlek T, Lindstedt RP, 1998, Joint Scalar-velocity pdf Modelling of Finite Rate Chemistry in a Scalar Mixing Layer, Combustion Science and Technology, Vol: 136, Pages: 303-331, ISSN: 0010-2202
The joint scalar-velocity probability density function (pdf) modelling approach is here applied to the problem of mixing and chemical reaction in a scalar mixing layer. The cases considered are of direct relevance to the modelling of turbulent combustion applications and the main objectives of the work are: (i) To assess the applicability of joint scalar-velocity pdf solution methods in the context of realistic low Damköhler number turbulent reacting flows. (ii) To investigate a multi-scalar extension of a modified binomial Langevin scalar mixing model of Valiño and Dopazo. The latter is here used in conjunction with the generalised Langevin model for velocity statistics of Haworth and Pope. The experimental data sets by Bilger et al., obtained in chemically reacting flows with Damköhler numbers of the order unity have been used to validate the approach. The excellent agreement obtained for both conserved and reacting scalars indicates that the reaction diffusion coupling is accurately represented by the binomial Langevin mixing model for this flow. Comparisons with linear-eddy model results of Kerstein are also presented.
Lindstedt RP, Meyer MP, Sakthitharan V, 1998, Direct simulation of transient spherical laminar flame structures, Eurotherm Seminar 61 on Detailed Studies of Combustion Phenomena, Pages: 53-74, ISBN: 9789038608105
Hulek T, Lindstedt RP, 1998, Joint scalar-velocity pdf modelling of finite rate chemistry in a scalar mixing layer, COMBUSTION SCIENCE AND TECHNOLOGY, Vol: 136, Pages: 303-331, ISSN: 0010-2202
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- Citations: 15
Lindstedt RP, 1998, Reduced chemistry submodels, International Flame Research Foundation (Guernsey)
Lindstedt RP, Leung K, 1998, Molecular growth processes in the gas phase, Preprints - American Chemical Society Division of Petroleum Chemistry, Vol: 43, Pages: 445-449, ISSN: 0569-3799
Perrin M, Garnaud A, Lasagni F, et al., 1998, TOPDEC Project: New tools and methodologies for the design of natural gas domestic burners and boilers, International Gas Research Conference (San Diego), Pages: 35-45, ISSN: 0736-5721
Toipadi AK, Danis AM, Mongla HC, et al., 1997, Soot modeling in gas turbine combustors
A method is presented for predicting soot in gas turbine combustors. A soot formation/oxidationmodel due to Fairweather et al [1992] has been employed. This model has been implemented in the CONCERT code which is a fully elliptic three-dimensional (3-D) body-fitted computational fluid dynamics (CFD) code based on pressure correction techniques. The combustion model used here is based' on an assumed probability density function (PDF) parameterized by the mean and variance of the mixture fraction and a β-PDF shape. In the soot modeling, two additional transport equations corresponding to the soot mass fraction and the soot number density are solved. As an initial validation, calculations were performed in a simple propane jet diffusion flame for which experimental soot concentration measurements along the center line and along the radius at various axial downstream stations were available from the literature. Soot predictions were compared with measured data which showed reasonable agreement Next, soot predictions were made in a 3-D model of a CF6-80LEC engine single annular combustor over a range of operating pressures and temperatures. Although the fuel in the combustor is Jet-A, the soot computations assumed propane to be the surrogate fuel. To account for this fuel change, the soot production term was increasedby a factor of 10X. In addition, theoxi dation term was increased by a factor of 4X to account for uncertainties in the assumed collision frequencies. The soot model w as also tested against two other combustors, a CF6-80C and a CFM56-5B. Comparison of the predicted soot concentrations with measured smoke numbers showed fairly good correlation within the range of the soot model parameters studied. More work has to be performed to address several modeling issues including sensitivity to oxidation rate coefficients and scalar diffusion.
Lindstedt RP, Skevis G, 1997, Chemistry of acetylene flames, Combustion Science and Technology, Vol: 125, Pages: 72-137, ISSN: 0010-2202
Acetylene constitutes one of the major intermediates in hydrocarbon flames and is important through its links to soot inception and mass growth processes. In the present study a detailed kinetic mechanism is developed and tested against experimental data for six lean (φ = 0.12) to sooting (φ = 2.50) laminar, premixed, low-pressure acetylene flames. Generally the agreement between computations and experiments is acceptable. It is suggested that OH attack competes with O attack as the major acetylene breakdown path in rich flames. It is further shown that the balancing of the ketyl radical destruction chemistry to a significant extent determines important flame features such as CO/CO2 ratio and H radical concentrations. The balancing of the methylene and methyne radical chemistry in both lean and rich environments is discussed in detail and the importance of molecular oxygen attack on 3CH2 is outlined. It is further shown that the present mechanism accurately predicts the qualitative evolution of methylene and methyne radical levels as a fucntion of stoichiometry. The present study incorporates the benzene oxidation mechanism by Lindstedt and Skevis (1994) and the benzene formation steps, involving isometrization reactions between linear and cyclic C6 intermediates, reported by Leung and Lindstedt (1995). The results obtained show that for rich acetylene flames the primary path for benzene formation passes via propargyl radical recombination and that benzene levels are generally satisfactorily predicted. However, computations also indicate that for leaner flames paths involving acetylene addition to n-C4H3 and 1,3-C3H5 radicals become increasingly important. This study also identifies reactions where further experimental investigations are required.
Lindstedt RP, Maurice LQ, 1997, Detailed chemical-kinetic model for aviation fuels, JOURNAL OF PROPULSION AND POWER, Vol: 16, Pages: 187-195, ISSN: 0748-4658
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- Citations: 107
Lindstedt RP, 1997, Systematically reduced kinetic models: A European perspective, 33rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference
Lindstedt RP, Skevis G, 1997, Chemistry of acetylene flames, COMBUSTION SCIENCE AND TECHNOLOGY, Vol: 125, Pages: 73-137, ISSN: 0010-2202
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- Citations: 112
Lindstedt RP, Vaos EM, 1997, Modelling of variable density effect in the second moment and dissipation equation for premixed turbulent flames, 11th Symposium on Turbulent Shear Flows, Pages: 36-41
Thomas SD, Bhargava A, Westmoreland PR, et al., 1996, Propene oxidation chemistry in laminar premixed flames, B SOC CHIM BELG, Vol: 105, Pages: 501-512
Computations have been performed in a lean (phi = 0.229), low pressure (p = 30 Torr) laminar premixed C3H6/O-2/Ar flame and comparisons with experiment made in order to assess existing uncertainties in the propene oxidation chemistry. It is shown that propene is mainly consumed by O atom addition reactions. However, reactions involving the OH radical remain important and a tentative branching ratio between abstraction and addition channels for the OH attack on C3H6 is also proposed. Furthermore, it has been shown that computed allyl radical levels are sensitive to the choice of rate for the molecular oxygen attack and a tentative product distribution for the latter is also proposed. Generally good agreement is obtained between computations and measurements for major flame features and key combustion intermediates. Moreover, allyl radical and total C3H4 levels are successfully reproduced. A tentative reaction mechanism for C-3 oxygenated species has also been formulated and validated against experimental data. Finally, the study identifies specific aspects of the propene oxidation chemistry where further theoretical and experimental work is required.
Lindstedt RP, Maurice LQ, 1996, Detailed kinetic modelling of toluene combustion, Combustion Science and Technology, Vol: 120, Pages: 119-167, ISSN: 0010-2202
A detailed chemical kinetic mechanism for the combustion of toluene has been assembled and evaluated for a wide range of combustion regimes. The latter include counterflow diffusion flames, plug flow reactors, shock tubes and premixed flames. The reaction mechanism features 743 elementary reactions and 141 species and represents an attempt to develop a chemical kinetic mechanism applicable to intermediate and high temperature oxidation. Toluene thermal decomposition and radical attack reactions leading to oxygenated species are given particular attention. The benzyl radical sub-mechanism is expanded to include izomerization and thermal decomposition reactions, which are important at flame temperatures, and a molecular oxygen attack path to form the benzylperoxy radical, which is found to be relevant at lower temperatures. The final toluene kinetic model results in excellent fuel consumption profiles in both flames and plug flow reactors and sensible predictions of the temporal evolution of the hydrogen radical and pyrolysis products in shock tube experiments. The structures of toluene/n-heptane, toluene/n-heptane/methanol and toluene/methanol diffusion flames are predicted with reasonable quantitative agreement for major and minor species profiles. Furthermore, the evolution of major and intermediate species in plug flow reactors is well modelled and excellent laminar burning velocity predictions have also been achieved.
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