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Luc Vervisch - One of the best experts on this subject based on the ideXlab platform.
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Modeling subgrid scale mixture fraction variance in LES of evaporating spray
Combustion and Flame, 2006Co-Authors: Cécile Pera, Luc Vervisch, Julien Reveillon, P. DomingoAbstract:Simulations of a dilute spray evaporating in spatially decaying homogeneous turbulence are performed. An Eulerian description of the flow is adopted, while the behavior of the discrete liquid phase is captured using Lagrangian Modeling. Time and length scales of the continuous carrier phase are fully simulated and by varying the properties of the modeled spray, a database of spray carrier phase direct numerical simulation (CP-DNS) is obtained. The CP-DNS is then filtered on a coarse grid to conduct a priori tests of subgrid scale (SGS) closures. The objective is to provide methods for approximating the level of SGS mixture fraction variance in large eddy simulation (LES) of fuel spray turbulent Combustion. Direct estimation of the variance from the scales resolved in LES is first discussed. Then, the solving of a balance equation to get the variance is addressed, with closures for the scalar dissipation rate and the correlation between vapor source and mixture fraction. From the results, a procedure to couple spray evaporation with SGS turbulent Combustion Modeling emerges.
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Combustion of residual steel gases: Laminar flame analysis and turbulent flamelet Modeling
Fuel, 2003Co-Authors: Olivier Gicquel, Guillaume Joncquet, Bernard Labegorre, Luc Vervisch, Nasser DarabihaAbstract:In recovery Combustion systems operating in the steel industry, energy is provided by boilers burning residual gases of blast furnace and coke oven. To help understand Combustion of this particular type of fuels, a numerical study is conducted where the major chemical properties of steel gas flames are collected. The chemical composition of representative fuel and oxidizer steel gas is varied over a large range in calculations using detailed chemistry and complex transport properties. The chemical equilibrium compositions, premixed flame speeds and diffusion flame extinction strain rates are determined. The advantages and shortcomings of the use of vitiated air emerge, and its introduction into the boiler appears as an interesting alternative to reduce NOxemission. The detailed information obtained with laminar flame calculations is also introduced in flamelet turbulent Combustion Modeling. Reynolds Averaged Navier Stokes (RANS) simulations of a test case burner are performed and some comparisons between numerical predictions and experimental results are presented. © 2002 Elsevier Science Ltd. All rights reserved.
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Turbulent Combustion Modeling
Progress in Energy and Combustion Science, 2002Co-Authors: Denis Veynante, Luc VervischAbstract:Numerical simulation of flames is a growing field bringing important improvements to our understanding of Combustion. The main issues and related closures of turbulent Combustion Modeling are reviewed. Combustion problems involve strong coupling between chemistry, transport and fluid dynamics. The basic properties of laminar flames are first presented along with the major tools developed for Modeling turbulent Combustion. The links between the available closures are illuminated from a generic description of Modeling tools. Then, examples of numerical models for mean burning rates are discussed for premixed turbulent Combustion. The use of direct numerical simulation (DNS) as a research instrument is illustrated for turbulent transport occurring in premixed Combustion, gradient and counter-gradient Modeling of turbulent fluxes is addressed. Finally, a review of the models for non-premixed turbulent flames is given.
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Spray vaporization in nonpremixed turbulent Combustion Modeling: a single droplet model
Combustion and Flame, 2000Co-Authors: Luc Vervisch, J. ReveillonAbstract:The injection of liquid fuel is a common procedure in turbulent Combustion devices operating in the nonpremixed regime. Various numerical models may be found in the literature to calculate such turbulent flames, using either Reynolds averaged Navier-Stokes techniques (RANS) or large eddy simulation (LES). The typical inputs of nonpremixed turbulent Combustion Modeling are the mean and the fluctuations of the mixture fraction. In computational fluid dynamics codes, the mean source of mixture fraction may be provided by Euler-Lagrange spray Modeling. However, the sources of fluctuations of mixture fraction due to vaporization require more closures. Direct numerical simulation (DNS) provides a way of estimating these sources and, using DNS of droplets evaporating in a turbulent flow, it is described how they play an important role in the time evolution of fuel/air mixing in a dilute spray. The statistical properties of the spray and of the scalar field are analyzed to propose a single droplet model (SDM) to evaluate these sources. SDM calculates mean values of the Eulerian source of fuel conditioned on the mixture fraction.
Mohand Tazerout - One of the best experts on this subject based on the ideXlab platform.
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Biodiesel from Waste Cooking Oil: Elaboration and Combustion Modeling
2015Co-Authors: Sary Awad, Mohand TazeroutAbstract:Modern society is facing two major problems: energy sources depletion and environment degradation because of wastes accumulation. The waste to energy vector contributes to simultaneous solutions of both problems. In this chapter biodiesel production via alkali catalyzed process was produced from waste cooking oils having different acid values. It was concluded that the yield of reaction and final product purity were sensitive to free fatty acid content of raw material, this remark is also true for optimal conditions. Yield of reaction decreased from 105 to 83% reported to oil mass by using waste cooking oil having 0.8 and 6.5 mgKOH/goil acid values respectively. Biodiesel produced from waste cooking oils having acid values lower than 6 mgKOH/goil respects European Norm limits. Produced biodiesel resulted in a 5% energy output increase while used on a diesel engine and a 20% increase in its energy consumption at 1500 rpm. Produced biodiesel was tested over the whole functioning engine range and correlations between operating conditions and heat release parameters were elaborated. The prediction model was compared to biodiesel produced from animal fat residues and the results were very satisfactory.
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Single zone Combustion Modeling of biodiesel from wastes in diesel engine
Fuel, 2013Co-Authors: Sary Awad, Edwin Geo Varuvel, Khaled Loubar, Mohand TazeroutAbstract:Increasing interest in diesel engine technology and the continuous demand of finding alternate fuels and reducing emissions has motivated over the years for the development of numerical models, to provide qualitatively predictive tools for the designers. Among the alternative fuels, biodiesel is considered suitable and the most promising fuel for diesel engine. The properties of biodiesel from waste oils are found similar to that of diesel. In this present work, a unique single zone Combustion model for diesel fuel and biodiesel was implemented to predict the cylinder pressure for the better understanding of Combustion characteristics of different fuels tested in a diesel engine and also to predict the Combustion and performance characteristics of the same engine running on different fuels. The single zone model coupled with a triple-Wiebe function was performed to simulate heat release between the period of IVC (inlet valve close) and EVO (exhaust valve open). This model also includes the submodels of intake and exhaust gases through the valves, ignition delay, burned fuel during the cycle and heat losses through walls to simulate all phases of Combustion. The model calibration was performed using data from experiments on diesel fuel and biodiesel from waste cooking oil. Later the same model was used to simulate the Combustion and the cylinder pressure of engine running on biodiesel derived from animal fat residues. Finally, cylinder pressure traces predicted by using single-zone model are compared to experimental pressure traces obtained from a diesel engine fuelled with diesel fuel and biodiesel. (C) 2012 Elsevier Ltd. All rights reserved.
Denis Veynante - One of the best experts on this subject based on the ideXlab platform.
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Training convolutional neural networks to estimate turbulent sub-grid scale reaction rates
Combustion and Flame, 2019Co-Authors: Corentin J. Lapeyre, Denis Veynante, Antony Misdariis, Nicolas Cazard, Thierry PoinsotAbstract:This work presents a new approach for premixed turbulent Combustion Modeling based on convolutional neural networks (CNN).1 We first propose a framework to reformulate the problem of subgrid flame surface density estimation as a machine learning task. Data needed to train the CNN is produced by direct numerical simulations (DNS) of a premixed turbulent flame stabilized in a slot-burner configuration. A CNN inspired from a U-Net architecture is designed and trained on the DNS fields to estimate subgrid-scale wrinkling. It is then tested on an unsteady turbulent flame where the mean inlet velocity is increased for a short time and the flame must react to a varying turbulent incoming flow. The CNN is found to efficiently extract the topological nature of the flame and predict subgrid-scale wrinkling, outperforming classical algebraic models.
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Towards the understanding of cyclic variability in a spark ignited engine using multi-cycle LES
Combustion and Flame, 2009Co-Authors: Olivier Vermorel, Stéphane Richard, Olivier Colin, Christian Angelberger, A. Benkenida, Denis VeynanteAbstract:Abstract Large-Eddy Simulation (LES) has been used to analyze the occurrence and the causes of cycle-to-cycle Combustion variations in a spark ignited four-valve single cylinder engine fueled with a homogeneous propane–air mixture. The Combustion Modeling combines an Eulerian model derived from the RANS AKTIM model that mimics the spark ignition and the Extended Coherent Flame Model (ECFM-LES) that describes the flame propagation. The motion of piston and valves is accounted for using an Arbitrary Eulerian Lagrangian (ALE) technique with body-fitted meshes. The computation covers nine consecutive complete four-stroke cycles following an initialization cycle. The obtained LES results are compared with experimental measurements. Although the number of computed cycles is fairly low, LES is shown to be able to reproduce both quantitatively and qualitatively the cyclic variability observed experimentally. The investigation of the possible causes of variability illustrates the unprecedented possibility LES offers for understanding cycle-to-cycle variations.
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Turbulent Combustion Modeling
Progress in Energy and Combustion Science, 2002Co-Authors: Denis Veynante, Luc VervischAbstract:Numerical simulation of flames is a growing field bringing important improvements to our understanding of Combustion. The main issues and related closures of turbulent Combustion Modeling are reviewed. Combustion problems involve strong coupling between chemistry, transport and fluid dynamics. The basic properties of laminar flames are first presented along with the major tools developed for Modeling turbulent Combustion. The links between the available closures are illuminated from a generic description of Modeling tools. Then, examples of numerical models for mean burning rates are discussed for premixed turbulent Combustion. The use of direct numerical simulation (DNS) as a research instrument is illustrated for turbulent transport occurring in premixed Combustion, gradient and counter-gradient Modeling of turbulent fluxes is addressed. Finally, a review of the models for non-premixed turbulent flames is given.
Andreas M Lippert - One of the best experts on this subject based on the ideXlab platform.
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stratified charge Combustion Modeling and imaging of a spray guided direct injection spark ignition engine
Proceedings of the Combustion Institute, 2005Co-Authors: Michael C Drake, Todd D Fansler, Andreas M LippertAbstract:Abstract Spray-guided spark-ignited direct-injection (SG-SIDI) engines are likely to be the next generation of gasoline engines. Compared to current wall-guided (WG-SIDI) engines, they offer improved fuel economy and substantially reduced hydrocarbon and soot emissions. Two stages of stratified Combustion (partially premixed flame propagation and mixing-controlled Combustion of rich products left from partial Combustion of initially fuel-rich mixtures) are investigated here in an experimental SG-SIDI engine using detailed CFD Modeling, high-speed spectrally resolved Combustion luminosity imaging, and cylinder pressure analysis. The CFD model reproduces the spatial and temporal distribution of both Combustion stages. Correlation of CFD calculations and experimental Combustion measurements demonstrates that optimum ignition timing occurs for somewhat rich equivalence ratios (0.9–1.6) and relatively low flow velocities (
P. Domingo - One of the best experts on this subject based on the ideXlab platform.
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Modeling subgrid scale mixture fraction variance in LES of evaporating spray
Combustion and Flame, 2006Co-Authors: Cécile Pera, Luc Vervisch, Julien Reveillon, P. DomingoAbstract:Simulations of a dilute spray evaporating in spatially decaying homogeneous turbulence are performed. An Eulerian description of the flow is adopted, while the behavior of the discrete liquid phase is captured using Lagrangian Modeling. Time and length scales of the continuous carrier phase are fully simulated and by varying the properties of the modeled spray, a database of spray carrier phase direct numerical simulation (CP-DNS) is obtained. The CP-DNS is then filtered on a coarse grid to conduct a priori tests of subgrid scale (SGS) closures. The objective is to provide methods for approximating the level of SGS mixture fraction variance in large eddy simulation (LES) of fuel spray turbulent Combustion. Direct estimation of the variance from the scales resolved in LES is first discussed. Then, the solving of a balance equation to get the variance is addressed, with closures for the scalar dissipation rate and the correlation between vapor source and mixture fraction. From the results, a procedure to couple spray evaporation with SGS turbulent Combustion Modeling emerges.