RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF

Naud, Bertrand; Novella, Ricardo; Pastor, J.M.; Winklinger, Johannes Fritz

doi:10.1016/j.combustflame.2014.09.014

Cited by 41 publications

(38 citation statements)

References 46 publications

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“…Note that so-called unsteady flamelet/progress variable approaches have also been proposed where both ideas are combined. In that case, igniting and extinguishing flamelets are resolved for different scalar dissipation rates, as for instance presented recently in [27,40]. However, such approaches require one additional control parameter, and a 3D lookup table needs to be considered in (Z, χ , Y c )-space, with χ the scalar dissipation rate.…”

Section: Combustion Modelmentioning

confidence: 99%

Transported PDF Modeling of Ethanol Spray in Hot-Diluted Coflow Flame

Naud

Roekaerts

2015

Flow Turbulence Combust

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This paper presents a numerical modeling study of one ethanol spray flame from the Delft Spray-in-Hot-Coflow (DSHC) database, which has been used to study Moderate or Intense Low-oxygen Dilution (MILD) combustion of liquid fuels (Correia Rodrigues et al. Combust. Flame 162, 759-773, 2015). A "Lagrangian-Lagrangian" approach is adopted where both the joint velocity-scalar Probability Density Function (PDF) for the continuous phase and the joint PDF of droplet properties are modeled and solved. The evolution of the gas phase composition is described by a Flamelet Generated Manifold (FGM) and the interaction by exchange with the mean (IEM) micro-mixing model. Effects of finite conductivity on droplet heating and evaporation are accounted for. The inlet boundary conditions starting in the dilute spray region are obtained from the available experimental data together with the results of a calculation of the spray including the dense region using ANSYS Fluent 15. A method is developed to determine a good estimation for the initial droplet temperature. The inclusion of the "1/3" rule for droplet evaporation and dispersion models is shown to be very important. The current modeling approach is capable of accurately predicting main properties, including mean velocity, droplet mean diameter and number density. The gas temperature is under-predicted in the region where the enthalpy loss due to droplet evaporation is important. The flame structure analysis reveals the existence of two heat release regions, respectively having the characteristics of a premixed and a diffusion flame. The experimental and modeled temperature PDFs are compared, highlighting the capabilities and limitations of the proposed model.

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Section: Combustion Modelmentioning

confidence: 99%

Transported PDF Modeling of Ethanol Spray in Hot-Diluted Coflow Flame

Naud

Roekaerts

2015

Flow Turbulence Combust

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“…The TFPV library is based on unsteady diffusion flame calculations performed with the TRIF model, in a similar way as done in [13,10,11] with the so-called approximated diffusion flames approach. Generation of the TFPV library is shown in Fig.…”

Section: Tabulated Flamelet Progress Variable (Tfpv)mentioning

confidence: 99%

“…Purpose of this work is the extension of the previously proposed approach for tabulated kinetics to include an additional combustion model as well as the possibility to predict NO x emissions. The model presented here, called TFPV (tabulated flamelet progress variable) was proposed in past works [10,11,13] and is based on the tabulation of laminar diffusion flamelets for different scalar dissipation rate levels. Compared to the multiple representative interactive flamelet model, TFPV is expected to perform better since it takes into account the local flow conditions and also transport of progress variable allow a more realistic description of the combustion process originated by multiple injections.…”

Section: Introductionmentioning

confidence: 99%

“…Within this context, a possible alternative for the reduction of CPU time can be represented by tabulated kinetics: chemical species reaction rates are stored in a table according to a specified mechanism and flame structure; then they are retrieved as function of the state of the system. The most widely used approaches consider a progress variable to characterize the advancement of the fuel oxidation reactions, by solving a transport equation with a source term which depends on local thermodynamic conditions, the progress variable itself and parameters characterizing the assumed flame structure, like the mixture fraction variance or the scalar dissipation rate [7,8,9,10,11]. In a previous work [12], the authors have implemented different models for Diesel combustion into the Lib-ICE code based on tabulated kinetics, demonstrating its consistency with the approaches based on direct-integration following extensive validation against the spray-A experimental data-sets from the Engine Combustion Network.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Validation of Combustion Models for Diesel Engines Based on Tabulated Kinetics in a Wide Range of Operating Conditions

Lucchini¹,

D’Errico²,

Cerri³

et al. 2017

SAE Technical Paper Series

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Computational fluid dynamics represents a useful tool to support the design and development of Heavy Duty Engines, making possible to test the effects of injection strategies and combustion chamber design for a wide range of operating conditions. Predictive models are required to ensure accurate estimations of heat release and the main pollutant emissions within a limited amount of time. For this reason, both detailed chemistry and turbulence chemistry interaction need to be included. In this work, the authors intend to apply combustion models based on tabulated kinetics for the prediction of Diesel combustion in Heavy Duty Engines. Four different approaches were considered: wellmixed model, presumed PDF, representative interactive flamelets and flamelet progress variable. Tabulated kinetics was also used for the estimation of N O x emissions. The proposed numerical methodology was implemented into the Lib-ICE code, based on the OpenFOAM R technology, and validated against experimental data from a light-duty FPT engine. Ten points were considered at different loads and speeds where the engine operates under both conventional Diesel combustion and PCCI mode. A detailed comparison between computed and experimental data was performed in terms of in-cylinder pressure and NO x emissions.

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“…Mixture fraction PDF is defined by the mean mixture fraction, Z, and its variance, Z 2 , parametrized with the segregation factor S determined by S = Z 2 /((Zsat − Z) Z). The variance of ln(χ), σ 2 , is assumed to be constant and equal to 2 [16].…”

Section: Model Descriptionmentioning

confidence: 99%

Influence of the chemical mechanism in the frame of diesel-like CFD reacting spray simulations using a presumed PDF flamelet-based combustion model

González

Oliver

Novella

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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The ability of a computational fluid dynamics (CFD) simulation to reproduce the diesel-like reacting spray ignition process and its corresponding flame structure strongly depends on both the fidelity of the chemical mechanism for reproducing the oxidation of the fuel and also on how the turbulence-chemistry interaction (TCI) is modeled. Therefore, investigating the performance of different chemical mechanisms not only in perfect stirred reactors but directly in the diesel-like spray itself is of great interest in order to evaluate their suitability for being further applied to CFD engine simulations. This research work focuses on applying a presumed probability density function (PDF) unsteady flamelet combustion model to the well-known spray A from the Engine Combustion Network (ECN), using three chemical mechanisms widely accepted by the scientific community as a way to figure out the influence of chemistry in the key characteristics of the combustion process in the frame of diesel-like spray simulations. Results confirm that in spite of providing all of them correct trends for ignition delays (ID) and lift-off lengths (LOL), when comparing with experimental results, the structure of the flame presents noticeable differences, especially in the low and intermediate temperatures and high equivalence ratio regions. Consequently, the selection of the chemical mechanism has an impact on the zones of influence of key species as observed in both spatial coordinates and also in the equivalence ratio-temperature maps. These differences are expected to be relevant considering the implications when coupling pollutant emissions models. The analysis of temperature and oxygen concentration parametric studies evidences how the observed differences are consistent and moderately dependent on the ambient conditions. KeywordsCombustion modeling, Chemical mechanism, Spray A, Flamelet IntroductionThe improvement of the combustion technologies in industrial devices, such as diesel engines, in terms of efficiency and pollutant emissions, evidence that a comprehensive knowledge of the processes involved is mandatory. Between the different processes that concur in the energetic transformation, turbulent non-premixed combustion appears as one of the most relevant. Nevertheless, its modeling is a complex issue due to the different length and time scales of the turbulence, the fuel oxidation and the interaction between them [1]. These considerations point out that for a proper modeling of the turbulent non-premixed combustion two main aspects are essential. The first one is the chemical mechanism, that determines the fuel oxidation, while the second one is the turbulence-chemistry interaction (TCI). Promoted by the need of gaining a very detailed knowledge in these issues in diesel spray conditions, the Engine Combustion Network (ECN) has proposed a set of experiments in controlled conditions that shed light for these concerns by means of experiments and numerical simulations. More particularly, the well-known spray A models a die...

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RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF

Cited by 41 publications

References 46 publications

Transported PDF Modeling of Ethanol Spray in Hot-Diluted Coflow Flame

Transported PDF Modeling of Ethanol Spray in Hot-Diluted Coflow Flame

Experimental Validation of Combustion Models for Diesel Engines Based on Tabulated Kinetics in a Wide Range of Operating Conditions

Influence of the chemical mechanism in the frame of diesel-like CFD reacting spray simulations using a presumed PDF flamelet-based combustion model

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