LES of Gas Exchange in IC Engines

Mittal, Varun; Kang, Seongwon; Doran, Eric; Cook, David; Pitsch, Heinz

doi:10.2516/ogst/2013122

Cited by 16 publications

(9 citation statements)

References 22 publications

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“…All scalars are discretized by Weighted Essentially NonOscillatory (WENO) schemes ensuring bounded solutions [23]. A more detailed description of the flow solver is given in Desjardins et al [24] and Mittal et al [25].…”

Section: Numerical Frameworkmentioning

confidence: 99%

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Davidovic

Falkenstein

Bode

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-A single-hole n-dodecane spray flame is studied in a Large-Eddy Simulation (LES) framework under Diesel-relevant conditions using a Multiple Representative Interactive Flamelets (MRIF) combustion model. Diesel spray combustion is strongly affected by the mixture formation process, which is dominated by several physical processes such as the flow within the injector, break-up of the liquid fuel jet, evaporation and turbulent mixing with the surrounding gas. While the effects of nozzle-internal flow and primary breakup are captured within tuned model parameters in traditional Lagrangian spray models, an alternative approach is applied in this study, where the initial droplet conditions and primary fuel jet breakup are modeled based on results from highly resolved multiphase simulations with resolved interface. A highly reduced chemical mechanism consisting of 57 species and 217 reactions has been developed for n-dodecane achiving a good computational performance at solving the chemical reactions. The MRIF model, which has demonstrated its capability of capturing combustion and pollutant formation under typical Diesel conditions in Reynolds-Averaged Navier-Stokes (RANS) simulations is extended for the application in LES. In the standard RIF combustion model, representative chemistry conditioned on mixture fraction is solved interactively with the flow. Subfilter-scale mixing is modeled by the scalar dissipation rate. While the standard RIF model only includes temporal changes of the scalar dissipation rate, the spatial distribution can be accounted for by extending the model to multiple flamelets, which also enables the possibility of capturing different fuel residence times. Overall, the model shows good agreement with experimental data regarding both, low and high temperature combustion characteristics. It is shown that the ignition process and pollutant formation are affected by turbulent mixing. First, a cool flame is initiated at approximately stoichiometric mixture and propagates towards the rich side. Hence, heat and radicals are transported away from the most reactive mixture and thus the ignition is delayed. At the same time, the transported heat and radicals increase the reactivity of rich mixtures, which strongly affects the CO formation. NO was found to increase compared to the no transport case due to enhanced mixing, which is related to a broader high-temperature zone and the additional transport of oxygen from lean into high-temperature regions.

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Section: Numerical Frameworkmentioning

confidence: 99%

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Davidovic

Falkenstein

Bode

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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“…During the pre-processing step, inter-grid coupling boundaries are defined as requested by the user. Finally, the parallel block decomposition as presented in [7], can be applied to all overset grids independently for different numbers of processors to conclude the pre-processing step.…”

Section: Overset Grid Methodsmentioning

confidence: 99%

“…However, meshing efforts are usually non-trivial. On the other hand, some engine LES studies have been performed based on structured Cartesian grids [6][7][8]. Major advantages of this approach are applicability of higher order numerical methods, reduced uncertainty with respect to LES mesh quality, insignificant meshing effort and computational performance.…”

Section: Introductionmentioning

confidence: 99%

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LES of Internal Combustion Engine Flows Using Cartesian Overset Grids

Falkenstein

Kang

Davidovic

et al. 2017

Oil & Gas Science and Technology - Rev. IFP Energies nouvel

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Accurate computations of turbulent flows using the Large-Eddy Simulation (LES) technique with an appropriate SubFilter Scale (SFS) model require low artificial dissipation such that the physical energy cascade process is not perturbed by numerical artifacts. To realize this in practical simulations, energy-conserving numerical schemes and high-quality computational grids are needed. If unstructured meshes are used, the latter requirement often makes grid generation for complex geometries very difficult. Structured Cartesian grids offer the advantage that uncertainties in mesh quality are reduced to choosing appropriate resolution. However, two intrinsic challenges of the structured approach are local mesh refinement and representation of complex geometries. In this work, the effectiveness of numerical methods which can be expected to reduce both drawbacks is assessed in engine flows, using a multi-physics inhouse code. The overset grid approach is utilized to arbitrarily combine grid patches of different spacing to a flow domain of complex shape during mesh generation. Walls are handled by an Immersed Boundary (IB) method, which is combined with a wall function to treat underresolved boundary layers. A statistically stationary Spark Ignition (SI) engine port flow is simulated at Reynolds numbers typical for engine operation. Good agreement of computed and measured integral flow quantities like overall pressure loss and tumble number is found. A comparison of simulated velocity fields to Particle Image Velocimetry (PIV) measurement data concludes the validation of the enhanced numerical framework for both mean velocity and turbulent fluctuations. The performance of two SFS models, the dynamic Smagorinsky model with Lagrangian averaging along pathlines and the coherent structure model, is tested on different grids. Sensitivity of pressure loss and tumble ratio to the wall treatment and mesh refinement is presented. It is shown that increased wall friction introduced by applying a wall model is overcompensated by some secondary effects, which lead to an overall reduction of pressure loss in the investigated engine geometry. Finally, dynamics of the statistically stationary valve jets are analyzed using Proper Orthogonal Decomposition (POD). Two distinct flow patterns are identified and the relevance for Cycle-to-Cycle Variations (CCV) is discussed.

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“…Modeling the flow behavior inside the combustion chamber using different numerical method is an important issue in the physical (aerospace and mechanical engineering) and mathematical (algebra and numerical methods of complex and bluff‐body) [1–28] contexts. Current problem concerns with a steady‐state two‐dimensional reaction between fuel and oxygen that enters from two different parallel locations openings (inlets) through combustion process that was modeled by coupled flow field and mass distribution subjected to the influence of a local discrete vortex.…”

Section: Introductionmentioning

confidence: 99%

Numerical conformal mapping method vs. geometrical separation attitude: Combustion motor chamber internal flow simulation

Nagler

2020

Z Angew Math Mech

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This paper describes the numerical solution of flow analysis in a two‐dimensional combustion chamber with two parallel inlets aided for propellants entrance, addressing a number of different problems that depend on each other: the flow affected by a discrete point in‐cell vortex, the velocity affected by the flow regime in the cell, and the combustion problem affected by the oxygen and fuel entries from the cell walls. The shape geometry of the combustion chamber is made from a square section connected with a semi‐circular one. The mathematical model of the problem consists of an inhomogeneous stream function Laplace equation coupled to partial differential mass conservation equation subjected to a wall non‐intrusion condition and known mass values in the wall openings. Algebraic conformal mapping transformation has been used for modeling the complex cell geometry. The solution was obtained by using the iterative Gauss–Seidel method for both the current function and the mass calculation. Comparison with another modeling method for calibration purpose was performed; considering each geometrical component separately whereas continuous conditions were applied between the two sections. The grid types are: (1) a uniform grid in Cartesian coordinates in the square part, and (2) a uniform circular grid in polar coordinates. It was found that different initial guesses have not effect on the final solution, but an informed initial guess affects the solution time convergence iterations number to solve the problem. Finally, the effect of the mixing vortex on the location of the flame front in the chamber was investigated.

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LES of Gas Exchange in IC Engines

Cited by 16 publications

References 22 publications

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

LES of Internal Combustion Engine Flows Using Cartesian Overset Grids

Numerical conformal mapping method vs. geometrical separation attitude: Combustion motor chamber internal flow simulation

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