Simulating kerosene / air flames with hybrid transported-tabulated chemistry (original) (raw)
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Description of kerosene / air combustion with Hybrid Transported-Tabulated Chemistry
Fuel, 2018
A strategy to introduce the detailed chemistry of kerosene-air combustion into simulations of flames is reported. Despite the rise in computer power achieved during the last decade, simulations of combustion chambers using detailed chemistry mechanisms are still not possible because of 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, by transporting only a reduced set of major species and tabulating the intermediate species while making use of their self-similarity property to downsize the table. HTTC has already been validated for light hydrocarbons such as methane. In this work, HTTC is extended to kerosene-air combustion showing that the number of species to be transported is unchanged compared to methane/air and that the self-similarity can still be applied. The chemistry of nitrogen oxides is also addressed with HTTC. The method allows for a reduction of the computational cost by around four orders of magnitude when computing laminar premixed flames. HTTC appears as a flexible tool since its prediction capabilities are maintained even if the table for intermediate species is generated in different conditions than those encountered in the simulation.
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.
Modeling Combustion Chemistry in Large Eddy Simulation of Turbulent Flames
Flow, Turbulence and Combustion, 2014
Flame ignition, stabilization and extinction or pollutant predictions are crucial issues in Large Eddy Simulations (LES) of turbulent combustion. These phenomena are strongly influenced by complex chemical effects. Unfortunately, despite the rapid increase in computational power, performing turbulent simulations of industrial configurations including detailed chemical mechanisms will still remain out of reach for a long time. This article proposes a review of commonly-used approaches to address fluid/chemistry interactions at a reduced computational cost. Several chemistry modeling routes are first examined with a focus on tabulated chemistry techniques. The problem of coupling chemistry with LES is considered in a second step. Examples of turbulent combustion simulations are presented in the final part of the article. Three LES applications are analyzed: a lean swirled combustor, a non-adiabatic turbulent stratified flame and a combustion chamber where internal recirculations promote the dilution of fresh gases by burnt gases. Keywords Turbulent combustion • Large Eddy Simulation • Tabulated chemistry • Complex chemistry 1 Introduction Combustion accounts for about 90 % of the global consumption of primary energy [1]. Despite its environmental impact this share will probably not fall in the near future. Combustion delivers energy which is immediately available through the exothermic conversion of gaseous, liquid or solid fuels. There are no other way to provide energy which are as convenient and as effective. In automotive or aerospace applications, combustion provides
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
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).
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.
Including real fuel chemistry in Large-Eddy Simulations
2017
Large-eddy simulation (LES) is progressively becoming a crucial design tool for the next generation of aeronautical combustion chambers. However, further improvements of the capability of LES is required for predicting pollutant emissions. Indeed, the detailed description of fuel pyrolysis and oxidation requires to take into account hundreds of chemical species involved in the complex non-linear reaction process. The direct integration of such detailed chemistry in LES is not a viable path, because of excessive computational demands and numerical stiffness. Modeling real transportation fuel is further complicated by the fact that kerosenes are complex blends of a large number of hydrocarbon compounds; the exact composition of which is very difficult to determine. In this work, the real-fuel combustion chemistry is described by the Hybrid Chemistry (HyChem) approach; and an LES-compliant Analytically Reduced Chemistry (ARC) is used to allow a direct integration of the fuel chemistry ...
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)
53rd AIAA Aerospace Sciences Meeting, 2015
A new correlated dynamic adaptive chemistry (CO-DAC) method is developed and integrated with the hybrid multi-timescale (HMTS) method for computationally efficient modeling of ignition and unsteady flame propagation of real jet fuel surrogate mixtures with a detailed and comprehensively reduced kinetic mechanism. A concept of correlated dynamic adaptive chemistry (CO-DAC) method in both time and space coordinates is proposed by using a few key phase parameters which govern the low, intermediate, and high temperature chemistry, respectively. Correlated reduced mechanisms in time and space are generated dynamically on the fly from the detailed kinetic mechanism by specifying thresholds of phase parameters of correlation and using the multi-generation path flux analysis (PFA) method. The advantages of the CO-DAC methods are that it not only provides the flexibility and accuracy of kinetic model and chemistry integration but also avoids redundant model reduction in time and space when the chemistry is frequently correlated in phase space. To further increase the computational efficiency in chemistry integration, the hybrid multi-timescale (HMTS) method is integrated with the CO-DAC method to solve the stiff ordinary differential equations (ODEs) of the reduced chemistry generated on the fly by CO-DAC. The present algorithm is compared and validated against the conventional VODE solver, DAC and HMTS/DAC methods for simulating ignition and unsteady flame propagation of real jet fuel surrogate mixtures consisting of four component fuels, n-dodecane, iso-octane, n-propyl benzene, and 1,3,5-trimethyl benzene. The results show the present HMTS/CO-DAC algorithm is not only computationally efficient but also robust and accurate. Moreover, it is shown that compared to the DAC and HMTS/ DAC methods, the computation time of model reduction in CO-DAC is almost negligible even for a large kinetic mechanism involving hundreds of species. In addition, the results show that computation efficiency of CO-DAC increases from homogeneous ignition to one-dimensional flame propagation for both the first and second generation PFA reduction. Therefore, the present HMTS/CO-DAC method can enable high-order model reduction and achieve higher computation efficiency for multi-dimensional numerical modeling. Published by Elsevier Inc. on behalf of The Combustion Institute.