Description of kerosene / air combustion with Hybrid Transported-Tabulated Chemistry (original) (raw)
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Simulating kerosene / air flames with hybrid transported-tabulated chemistry
2015
A strategy to introduce the detailed chemistry of kerosene combustion into direct numerical simulations of flames is reported. During the last decade, significant progress has been made to improve the chemical kinetic and turbulent combustion modeling as well as the high-performance computer power. However, a large-eddy simulation of an aeronautical combustion chamber using detailed chemistry mechanisms is still not possible because of the needed temporal resolution and the large number of species to be transported. The hybrid transported-tabulated chemistry method (HTTC) has been designed to overcome these obstacles and radically reduce the computational cost of such simulations, by transporting only a reduced set of major species and tabulating the intermediate species while making use of their selfsimilarity property to downsize the table. In this work, the application of HTTC to kerosene combustion is investigated. Although intermediate heavy species typical of kerosene combusti...
Flow, Turbulence and Combustion, 2014
ABSTRACT A strategy to introduce hydrocarbon combustion detailed chemistry into three-dimensional numerical simulation of flames is reported. Significant progress has been made recently in terms of accuracy and robustness in both chemical kinetics and flow computations. However, the highest resolution reached in simulation of practical burner does not yet ensure that the response of intermediate radical species is fully captured. In the method discussed, the full set of species and elementary reaction rates of the detailed mechanism are retained, but only species featuring non-zero concentration in fresh and burnt gases are transported with the flow. Intermediate chemical species, developing within thin flame layers, are expressed resorting to their self-similar properties observed in a series of canonical combustion problems, projected into an optimized progress variable defined from all transported species. The method is tested with success in various adiabatic and non-adiabatic laminar steady- and unsteady-strained premixed flames.
Hybrid transported-tabulated chemistry for partially premixed combustion
Computers & Fluids, 2019
The integration of combustion chemistry into a fully compressible numerical solver is presently achieved using the hybrid transported-tabulated chemistry (HTTC). With HTTC, the main species are transported while most minor species are tabulated, which means that differences with a fully transported chemistry (FTC) solver are limited and concern mainly table reading for minor species. The implementation steps of HTTC are given in detail and an optimization of the code is proposed by tabulating the properties of the pure species as well as the reaction rates of the elementary reactions as a function of the temperature to speed up simulations. The original version of HTTC, validated for premixed combustion, has been also extended to partially premixed combustion by adding a prolongation of the lookup table for minor species outside the flammability limits. Two strategies are proposed and evaluated on a methane / air edge flame featuring a very high mixing fraction gradient. The results agree favorably by comparison with a reference flame simulated with a detailed chemistry. As the minor species are no longer transported with the flow using HTTC, the calculation cost is found divided by about 5 compared to the FTC solver.
2008
The development of new fuels and combustion devices would be greatly accelerated if we could build and solve accurate predictive models of the combustion chemistry in these devices. This is the most important technical challenge facing the combustion community. Recent advances on several fronts suggest that this should soon be possible. Here we review some developments in automated mechanism construction, methods for estimating for the chemical parameters, numerical solution algorithms, and in procedures by which the entire combustion community can contribute to meeting this important technical challenge. 日本燃焼学会誌 第 50巻 151号(2008年)
Tabulation of complex chemistry based on self-similar behavior of laminar premixed flames
Combustion and Flame, 2006
Detailed mechanisms describing complex phenomena of combustion chemistry, such as flame propagation or pollutant formation, involve hundreds of species and thousands of elementary reactions and cannot be handled in practical simulations of turbulent combustion. A widely used way to reduce chemistry is to build look-up tables where chemical parameters such as reaction rates and/or species mass fractions are determined from a reduced set of coordinates (ILDM, FPI, or FGM methods). Nevertheless, these tables may require large memory spaces and nonnegligible access times, especially when running on massively parallel computers. In this work, the self-similarity behavior of laminar premixed flames is first put into evidence and then theoretically sustained. This property provides a way to reduce the size of chemical databases, especially for computations on massively parallel machines, under the FPI (flame prolongation of ILDM) framework. The database is reduced to similarity profiles for the species reaction rates (or the species mass fractions), stored together with scaling rules. This new formulation is then implemented in the PREMIX code and numerical simulations of laminar premixed flames successfully compare with full chemistry computation, validating this promising approach.
Computationally efficient implementation of combustion chemistry usingin situadaptive tabulation
Combustion Theory and Modelling, 1997
A computational technique is described and demonstrated that can decrease by three orders of magnitude the computer time required to treat detailed chemistry in reactive flow calculations. The method is based on the in situ adaptive tabulation (ISAT) of the accessed region of the composition space-the adaptation being to control the tabulation errors. Test calculations are performed for non-premixed methane-air combustion in a statisticallyhomogeneous turbulent reactor, using a kinetic mechanism with 16 species and 41 reactions. The results show excellent control of the tabulation errors with respect to a specified error tolerance; and a speed-up factor of about 1000 is obtained compared to the direct approach of numerically integrating the reaction equations. In the context of PDF methods, the ISAT technique makes feasible the use of detailed kinetic mechanisms in calculations of turbulent combustion. The technique can also be used with reduced mechanisms, and in other approaches for calculating reactive flows (e.g. finite difference methods).
Impact of detailed chemistry and transport models on turbulent combustion simulations
Progress in Energy and Combustion Science, 2004
More and more publications can be found in recent years where detailed models are employed to describe the chemical and molecular transport processes controlling flame structure. Up to a recent past, such studies were restricted to simple zero-or one-dimensional laminar computations, like ignition in a fully premixed mode, freely propagating laminar premixed flames or counter-flow flames. Since such models are now often used to investigate turbulent flames in multi-dimensional computations, we feel it is useful to review the literature on this subject and give a synthesis of the obtained results. To be more specific, we consider only in this review publications where (1) chemical processes are modeled with a multi-step reaction scheme, taking at least an intermediate species into account; or (2) molecular diffusion processes of the individual species are represented by a more elaborate model than assuming unity Lewis numbers; and (3) the retained configuration leads to unsteady strain-rate and curvature (or stretch-rate) variations in the reaction zone. Over 200 recent publications have been found to respect these criteria. Summarizing the results, one can say that there appears to be a growing need for simulations relying on detailed models for chemistry and transport processes, probably due to the fact that restrictions concerning pollutant emissions motivate a request for more accurate, quantitative results. Progress must still be accomplished concerning the identification of chemical pathways, the accurate determination of rate constants, and the development of reliable but efficient chemistry reduction techniques. The impact of the retained molecular diffusion model is higher than expected at the beginning of this study. Even for turbulent configurations, the global impact of these models can be comparable to switching between two different detailed chemical schemes. Concerning local flame structure, the transport models play an essential role, in particular for high flame curvatures and far from stoichiometry. As a whole, the need for matching the accuracy level of the chosen chemical and transport models is emphasized, since describing a physical phenomenon in great detail while, at the same time, representing another phenomenon of comparable importance with a very rough model, prevents really quantitative (and even perhaps qualitative) predictions. Specific difficulties concerning validation are also identified. q
Fuel, 2012
Chemistry tabulation has been widely used in the literature to introduce some of the major subtleties of detailed chemistry in turbulent flame simulations. In the case of combustion systems featuring numerous degrees of freedom-such as progress of reaction, equivalence ratio, pressure, enthalpy, dilution by burnt gases-the rapidly growing size of the lookup-table file becomes one of the factor limiting chemistry introduction in high performance computing, because the database needs to be loaded on every processor whose memory is limited. A multi-zone self-similar chemistry tabulation technique is proposed to overcome this limitation, in both the cool-flame and the high-temperature flame regimes. A formalism is first developed for seeking self-similar behavior in auto-ignition. The resulting tabulation strategy is limited to the storage of a few profiles, to which algebraic relations are added. In the case of auto-igniting mixture, it is shown that major species of n-heptane-air and methane-air combustion can be captured by a single-set of self-similar profiles, opening perspectives for chemistry tabulation of multi-component liquid fuels.
Improved Chemical Kinetics Numerics for the Efficient Simulation of Advanced Combustion Strategies
SAE Int. J. Engines 7(1):2014, doi:10.4271/2014-01-1113
The incorporation of detailed chemistry models in internal combustion engine simulations is becoming mandatory as local, globally lean, low-temperature combustion strategies are setting the path towards a more efficient and environmentally sustainable use of energy resources in transportation. In this paper, we assessed the computational efficiency of a recently developed sparse analytical Jacobian chemistry solver, namely ‘SpeedCHEM’, that features both direct and Krylov-subspace solution methods for maximum efficiency for both small and large mechanism sizes. The code was coupled with a high-dimensional clustering algorithm for grouping homogeneous reactors into clusters with similar states and reactivities, to speed-up the chemical kinetics solution in multi-dimensional combustion simulations. The methodology was validated within the KIVA-ERC code, and the computational efficiency of both methods was evaluated for different, challenging engine combustion modeling cases, including dual fuel, dual direct-injection and low-load, multiple-injection RCCI, direct injection gasoline compression ignition (GDICI), and HCCI engine operation using semi-detailed chemistry representations. Reaction mechanisms of practical applicability in internal combustion engine CFD simulations were used, ranging from about 50 up to about 200 species. Computational performance for both methods was observed to reduce the computational time for the chemistry solution by up to more than one order of magnitude in comparison to a traditional, dense solution approach, even when employing the same high-efficiency internal sparse algebra and analytical formulations. This confirms that consideration of detailed chemistry is not a bottleneck anymore, allowing use of larger and more refined meshes. Further research that focused on algorithms for fast and efficient advection with a large number of species is suggested.
Computers & Fluids, 2012
This paper presents a dimension reduction technique for turbulent non-premixed flames based on a chemical equilibrium method combined with a reaction calculation. An advantage of the proposed technique is that it simplifies the process of building a reduced chemical mechanism according to the accuracy requirement for the chemical species. The proposed technique reduces the computational time for the combustion simulation. In this technique, chemical species are roughly divided into two groups: The first includes fuels and intermediate species; the intermediate species include only those necessary for high accuracy. The second group comprises the rest of the species, and their mass fractions are obtained from a look-up table prepared using chemical equilibrium calculations conducted prior to the combustion simulation. The obtained results were compared with the experimental data of a CO-H 2air turbulent non-premixed flame and computational data obtained using the eddy dissipation concept (EDC) model. The major mass fractions of CO, H 2 , and H 2 O, as well as the temperature and mixture fraction obtained using the proposed technique, were in good agreement with these reference data. Furthermore, compared with the EDC model, the minor mass fractions of OH, O, and NO obtained using the proposed technique were close and the computational time was 75% lower.