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- Huang, Chen, 1981, et al.
(författare)
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A Numerical Study on Stratified Turbulent Combustion in a Direct-Injection Spark-Ignition Gasoline Engine Using an Open-Source Code
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, a free, open source CFD software package called OpenFOAM has been attracting increasing amounts of attention as a promising, inexpensive, and efficient CFD tool for the numerical simulation of processes such as fuel injection and evaporation, turbulent mixing and burning. Here, we describe the further development of OpenFOAM to enable its use in simulating stratified turbulent combustion in DI SI engines. Advanced models of various phenomena relevant to partially premixed turbulent flames were implemented into the code, and the effects of these implementations were investigated by performing unsteady 3D RANS simulations of stratified turbulent burning in a DI SI engine. First, the Flame Speed Closure (FSC) model of premixed turbulent combustion was implemented. Second, a method for evaluating the mean density in premixed turbulent flames that is available in the standard OpenFOAM library was improved. Third, a semi-detailed chemical mechanism was introduced to describe the influence of the equivalence ratio, pressure, and temperature of the unburned gas on the burning rate and flame temperature. The flame temperature and laminar flame speed are computed, approximated and further implemented into the OpenFOAM library. Fourth, to address the influence of turbulent fluctuations in mixture composition on mean variables, a presumed Favre beta-PDF for the mixture fraction was implemented. Fifth, the implementation of the balance equation for mixture fraction variance was improved with the consideration for the evaporation source term. Finally, the mean burning rates computed with and without the aforementioned models were compared to assess the importance of the studied effects.
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| 2. |
- Huang, Chen, 1981, et al.
(författare)
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Application of Flame Speed Closure Model to RANS Simulations of Stratified Turbulent Combustion in a Gasoline Direct-Injection Spark-Ignition Engine
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:1, s. 98-131
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Taylor & Francis. The present work aims at development and validation of a tool for numerically modeling stratified turbulent combustion in a gasoline direct injection (GDI) engine. For this purpose, an open source code called OpenFOAM ® , which has been attracting growing interests from both industries and academies due to an opportunity to access the source code and to test new models without paying license fees, is further developed by implementing advanced models relevant to stratified turbulent burning. In particular, first, the Flame Speed Closure model of premixed turbulent combustion is implemented in order to simulate flame propagation through inhomogeneously premixed reactants. Second, a newly calculated approximation of the laminar flame speed of gasoline-air mixtures as a function of the equivalence ratio, pressure, and temperature is implemented in order to simulate dependence of burning rate on the local mixture composition. Third, a newly calculated approximation of the combustion temperature of gasoline-air mixtures as a function of the equivalence ratio, pressure, and product enthalpy is implemented in order to allow for dissociation of combustion products and heat losses. Fourth, a presumed mixture-fraction probability density function (PDF) approach is implemented in order to simulate the influence of turbulent fluctuations in the mixture fraction on the local burning rate. In addition to commonly used mass-weighted mixture-fraction PDF, a more consistent model that deals also with the canonical mixture-fraction PDF is developed and the two approaches are compared. Numerical results that show the influence of the aforementioned implementations on computed global characteristics of stratified combustion in a research GDI engine are discussed. The developed numerical tool is quantitatively validated by comparing computed pressure traces in the GDI engine with experimental data obtained in three different cases associated with two different loads, late injection timings, and short time intervals between the injection and spark ignition.
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| 5. |
- Yasari, Ehsan, 1983, et al.
(författare)
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Assessment of a Recent Model of Turbulent Scalar Flux in RANS Simulations of Premixed Bunsen Flames (short paper)
- 2015
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Ingår i: Turbulence Heat and Mass Transfer 8, Proceedings of the Eight International Symposium on Turbulence, Heat and Mass Transfer 8, Sarajevo, Bosnia and Herzegovina, 15-18 September, 2015, Eds. by K. Hanjalic, T. Miyauchi, D. Borello, M. Hadziabdic, and P. Venturini, Begel House Inc., New York. - 2377-2816. ; , s. 533-536
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Konferensbidrag (refereegranskat)
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| 6. |
- Yasari, Ehsan, 1983
(författare)
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Extension of OpenFOAM Library for RANS Simulation of Premixed Turbulent Combustion
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unsteady multi-dimensional numerical simulation of turbulent flames is a well recognized tool for research and development of future internal combustion engines capable for satisfying stringent requirements for ultra-low emission and highly efficient energy conversion. To attain success, such simulations need, in particular, well elaborated Computational Fluid Dynamics (CFD) software, as well as advanced predictive models of turbulent burning. As far as the software is concerned, a free, open source CFD software package called OpenFOAM (Open Field Operation And Manipulation) library has attracted increasing amounts of attention from both commercial and academic organizations over the past years. While the number of problems that have been studied using the package grows fast, applications of the code to Reynolds-Averaged Navier-Stokes (RANS) simulations of premixed turbulent flames are still rare and the standard version of OpenFOAM does not contain implementation of premixed turbulent combustion models with well documented predictive capabilities. Therefore, one goal of the present work was to further develop the code for multi-dimensional RANS simulations of premixed turbulent flames. As far as models are concerned, a number of models of turbulent burning have been proposed to be used, but they strongly need straightforward quantitative testing against a wide and representative set of experimental data obtained in well defined simple cases under substantially different conditions. Therefore, another goal of the present work was to further validate two advanced models of the influence of turbulence on premixed combustion, i.e. the so-called Turbulent Flame Closure (TFC) and Flame Speed Closure (FSC) models. The two models were implemented into OpenFOAM library and the so-extended code was successfully applied to simulate two widely recognized sets of experiments with two substantially different, well-defined, simple, laboratory premixed turbulent flames, i.e. (i) oblique, confined, preheated, highly turbulent, methane-air flames experimentally studied by Moreau and (ii) V-shaped, open, weakly turbulent, lean methane-air flames investigated by Dinkelacker and Hölzler under the room conditions. The obtained numerical results agree both qualitatively and quantitatively with the aforementioned experimental data, thus, validatingboth the implemented combustion models and the extended code. It is worth stressing that the influence of variations in the equivalence ratio on the measured data was quantitatively predicted without tuning. The capabilities of the TFC and FSC models and the extended code to well predict turbulent burning rates for various equivalence ratios make these two models and the code particularly interesting for multi-dimensional unsteady RANS simulations of turbulent combustionin Direct Injection Stratified Charge (DISC) Spark Ignition (SI) engines.
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| 7. |
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| 8. |
- Yasari, Ehsan, 1983
(författare)
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RANS Simulations of Interaction between Premixed Flame and Turbulence using OpenFOAM Library
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unsteady multi-dimensional numerical simulation of turbulent flames is a widely recognized tool for research and development of future internal combustion engines capable of satisfying stringent requirements for ultra-low emission and highly efficient energy conversion. To attain success, such simulations need, in particular, elaborated CFD software and predictive models of turbulent burning. Accordingly, the present work aimed at implementing advanced models of flame turbulence interaction into an open-source CFD package called OpenFOAM, which has been attracting increasing amounts of attention from both commercial and academic organizations, but has yet been rarely assessed in CFD studies of premixed turbulent flames. Subsequently, the extended code was applied to RANS simulations of various experiments with premixed turbulent flames in order to validate the code and the models implemented into it.More specifically, first, the influence of turbulence on combustion was addressed using the so-called Turbulent Flame Closure (TFC) and Flame Speed Closure (FSC) models. The former model has already been tested against a wide range of targets, whereas its extension known as the FSC model has yet been mainly validated against experimental data obtained from expanding flames. In the present study, the two modelswere implemented into OpenFOAM and the so-extended code was successfully applied to RANS simulations of four widely recognized sets of experiments with substantially different laboratory premixed turbulent flames. Simulations of these four experiments provided detail assessment of the TFC and FSC models by varying flame configuration, turbulence intensity, ambient temperature, mixture composition, etc. Moreover, because all the simulated flames were statistically stationary, the performed tests substantially extended the domain of validation of the FSC model. Numerical results obtained using the FSC model agree both qualitatively and quantitatively with the experimental data,thus, validating both the model and its implementation into OpenFOAM. Second, in order to address the influence of combustion on turbulent transport, a recent simple model of turbulent scalar flux in premixed flames was extended and implemented into OpenFOAM. Subsequently, the so-extended code was applied to RANS simulations of two widely recognized sets of experiments in that countergradient turbulent scalar flux was documented. Obtained numerical results indicate that the model is capable of predicting the countergradient turbulent scalar transport in weakly turbulent flames, as well as transition to gradient scalar transport with an increase in a ratio of the rms turbulent velocity to the laminar flame speed. These results are encouraging and justify further joint applications of (i) the FSC model of the influence of turbulence on combustion and (ii) the simple model of turbulent transport in flames to RANS simulations of burning in engines. The joint use of the two models allows researchers to evaluate the mean rate of product creation on a post-processing stage and, subsequently, to use this rate for simulating emissions.
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| 10. |
- Yasari, Ehsan, 1983, et al.
(författare)
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RANS simulations of statistically stationary premixed turbulent combustion using Flame Speed Closure model
- 2015
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Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 94:2, s. 381-414
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent Flame Closure (TFC) and Flame Speed Closure (FSC) models of the influence of turbulence on premixed combustion are applied to RANS simulations of five sets of experiments with (i) highly turbulent, oblique, confined ONERA flames under elevated temperatures, (ii) highly turbulent, conical, confined PSI flames under elevated temperatures and pressures, (iii) open V-shaped flames, and weakly turbulent Bunsen (iv) Erlangen and (v) Orl,ans flames under the room conditions. Besides flame geometry, pressure, and initial temperature, bulk flow velocities, turbulence characteristics, and mixture compositions are different in these five sets of flames, with the equivalence ratio being varied in each set. Turbulence is modeled invoking either the standard or RNG k - epsilon model. The same standard value A = 0.5 of a single constant of the TFC or FSC model is used in all these simulations, but certain input parameters of the turbulence model are tuned by investigating a single reference case for each set of flames. The TFC and FSC combustion models yield similar results when simulating the PSI flames, but the FSC model shows better performance in predicting burning rate for four other sets of flames. All in all, results computed using the FSC model agree reasonably well with the majority of the experimental data utilized to test the model, with a few exceptions discussed in the paper.
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