| 1. |
- Golovitchev, Valeri, 1945, et al.
(författare)
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Ignition: New Application to combustion Studies
- 2010
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Ingår i: Handbook of Combustion Vol.1: Fundamentals and Safety. - 9783527324491 ; , s. 85-106
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Kärrholm Peng, Fabian, 1980, et al.
(författare)
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MODELLING INJECTOR FLOW INCLUDING CAVITATION EFFECTS FOR DIESEL APPLICATIONS
- 2007
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Ingår i: ASME Fluids Engineering Conference.
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Konferensbidrag (refereegranskat)abstract
- In this paper, cavitation and pressure parameters measuredin a model diesel injector are compared to data acquired by numericalsimulations using a new code developed for the Open-FOAM platform, which uses a barotropic equation of state togetherwith the homogeneous equilibrium assumption. It is aviscid code, allowing both compressible liquid and vapour tobe modelled. The mass flow and cavitation probabilities obtainedfrom the simulations are compared to data obtained inexperiments performed at AVL’s laboratories, in which the flowthrough an almost two-dimensional nozzle was examined. Theexperimental data used include pressure profiles and cavitationimages. The model proved to be able to predict cavitation probabilities,mass flows, and the occurrence of super-cavitation inthe channel. In addition, it proved to be stable in its dependencyon physical parameters, and grid independent.
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| 3. |
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| 4. |
- Kärrholm Peng, Fabian, 1980
(författare)
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Numerical Modelling of Diesel Spray Injection and Turbulence Interaction
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It has been established by many authors that numerical simulations ofDiesel sprays, using a Lagrangian description for the liquid phase,are particularly sensitive to the scale of the computational cellscompromising the mesh. There have been many suggestions regardingmeans to reduce the dependency on the mesh by improving the componentsubmodels, but few have addressed the gas phase turbulence modelling. This thesis covers two main topics. The first is the application ofcavitation models in order to develop a new primary atomization modelfor Diesel spray. The second is to investigate the effect of modifyingthe length scale used in turbulent dispersion models for particles inturbulent flows. The goal of the nozzle flow calculations is to develop a newatomization model, that does not have the drawback of requiring eithernon-physical parameters or information derived from specificexperiments. To validate the cavitation simulations, comparisons withexperimental data obtained at AVL were made. The experiments showvelocity profiles and pressure contour, and are practically2D. The results of the cavitaiton simulations do notrepresent reality to a satisfactory degree yet. Therefore, a newatomization model has not been developed. Since most industrial applications are based on eddy viscosityk-epsilon type models, the spray investigations were limitedto this kind of turbulence model. Three versions were tested, the goalwas to evalute their effect on the spray behaviour and sensitivity tomesh resolution. This thesis shows that the turbulence model plays a significant rolein the sprays' behaviour on grids of different spatial resolution, anda simple and efficient way to reduce the dependency of the meshresolution, by limiting the turbulent length scale in the liquid coreregion, is proposed. It is shown that this constraint has a positiveeffect on the spray behaviour, and reduces grid dependence.
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| 5. |
- Kärrholm Peng, Fabian, 1980
(författare)
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Numerical Modelling of Diesel Spray Injection, Turbulence Interaction and Combustion
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis covers two main topics. The first is numerical modelling ofcavitating diesel injector flows, focusing on describing suchflows using asingle-phase cavitation model based on a barotropic equation of statetogetherwith a homogenous equilibrium assumption. The second topic isEuler-Lagrangian simulations of diesel sprays, focusing on attempts to reducethe high grid/timestep dependencies in numerical simulations of dieselsprays.In addition, the ability of two CFD codes to predict flamelift-off length andignition delay time, and the advection scheme’s influence on fueldistributions,are considered.A long-term goal was to develop a new atomization model based on calculatedflows in injector nozzles, which did not have the drawback ofrequiring eithernon-physical parameters or information derived from specificexperiments. Tovalidate the cavitation simulations, comparisons were made with experimentaldata obtained at AVL. The experimental data (which are practically 2D)provide information on velocity profiles and pressure contours.These datawere used to validate the code. However, since the code is not stable fordiesel-type pressures, no atomization model was developed.The main part of the thesis describes how diesel sprays were simulated usingthe discrete droplet model (DDM), in which the liquid is described byLagrangian coordinates and the vapour by an Eulerian approach. Thesimulations have been used to investigate how the k-ε family ofturbulencemodels influence spray behaviour, and a simple but efficientway to reduce thedependency of the mesh resolution, by limiting the turbulence length scale inthe liquid core region, is proposed. This constraint is shown to have apositiveeffect on the spray behaviour, and to reduce both grid and timestepdependencies.In addition, the ignition delay time and flame lift-offlengths have beeninvestigated, since these two properties are believed to be important foremissions formation. The simulations used a complex chemical mechanisminvolving 83 species and 338 reactions. The effects of the numericalscheme,the turbulence model and physical parameters (like ambient temperature andoxygen content) on these variables have also been investigated.
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| 6. |
- Kärrholm Peng, Fabian, 1980, et al.
(författare)
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On Performance of Advection Schemes in the Prediction of Diesel Spray and Fuel Vapour Distributions
- 2008
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Ingår i: ILASS 2008, Como Lake.
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Konferensbidrag (refereegranskat)abstract
- We have investigated the performance of advection schemes (focusing mainlyon Total Variation Diminishing, TVD, schemes)applied in modelling diesel sprays, and assessed their influence on liquidspray penetration and fuel vapour distribution. Here,we compare sprays simulated using several types of TVD schemes (Superbee,MUSCL, limited Linear, and UMIST) – andstandard upwind and linear schemes as references – in conjunction withthree different turbulence models (standard, RNG andLaunder-Sharma k-ε models), to non-reacting diesel sprays observed inthe Sandia high-pressure, high-temperature constant-volume vessel. The OpenFOAM CFD code was used for all of the simulationsdescribed. In addition to comparing thesimulations to experimental data, we provide overall assessments of theperformance and utility of the TVD schemes in multi-dimensional diesel modelling.
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| 7. |
- Kärrholm Peng, Fabian, 1980, et al.
(författare)
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Three-Dimensional Simulation of Diesel Spray Ignition and Flame Lift-Off Using OpenFOAM and KIVA-3V CFD Codes
- 2008
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional simulations of ignition and combustion of a dieselspray were conducted. The primary goal of the work was to compare twodifferent CFD codes: OpenFOAM, an object-oriented C++ based code, andKIVA-3V. The spray is modelled by the Eulerian-Lagrangian approach inboth codes, with several common submodels. Some important sub-modelsimplemented include \emph{inter alia} aKelvin-Helmholtz/Rayleigh-Taylor (KH/RT) model for spray break-up, animproved spray collision model, and a Partially Stirred Reactor (PaSR)model for turbulence-chemistry interaction. Both CFD codes solve thechemical reaction equations in a fully coupled manner. A cubic-shaped Cartesianmesh was used in the KIVA-3V simulations, while a polyhedral meshincluding a combination of hexagonal and prism-shaped cells wasconstructed for the OpenFOAM computations.The effects of high EGR and ambient temperature on the ignition and flamelift-off processes of a diesel spray were investigated. Sandia experimentsconducted in a high-pressure and high-temperature constant-volume vessel werechosen for the simulations and validations. A single spray was injected intothe vessel, and EGR was mimicked by reducing the oxygen concentration. Thediesel reference fuel (n-heptane) was considered. For the study, a medium-sizemechanism involving 83 species and 338 reactions was employed. The mechanismwas validated using the CHEMKIN II package and the reaction rate constantswere adjusted on the basis of measurements of auto-ignition delays ofn-heptane/air mixtures in shock-tube experiments (with equivalence ratiosranging from 0.2 to 0.4 at 50 bar, and from 0.5 to 2.0 at 13.5 bar and 41.0bar), laminar flame speeds (1 atm and 3 atm), and flame structure inburner-stabilized premixed flames (1 atm).The simulations demonstrate that both CFD codes are capable of spray ignitionand combustion studies, though both show stronggrid-dependence. The numerical results show that the ignition delay,flame lift-off and combustion temperature of the spray are stronglyinfluenced by EGR and ambient gas temperature. These predictions arein agreement with measurements. Nevertheless, differences are observedbetween the results predicted by OpenFOAM and those from KIVA-3V, forexample, the flame predicted by the former is thinner and longer than that by thelatter, which requires further investigation.
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