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Tampere University of Technology Modelling of Spray Combustion, Emission Formation and Heat Transfer in Medium Speed Diesel Engine Citation Taskinen, P (2005) Modelling of Spray Combustion, Emission Formation and Heat Transfer in Medium Speed Diesel Engine (Tampere University of Technology Publication; Vol 562) Tampere University of Technology Year 2005 Version Publisher's PDF (version of record) Link to publication TUTCRIS Portal (http://www.tut.fi/tutcris) Take down policy If you believe that this document breaches copyright, please contact tutcris@tut.fi, and we will remove access to the work immediately and investigate your claim Download date:05.05.2018 Julkaisu 562 Publication 562 Pertti Taskinen Modelling of Spray Combustion, Emission Formation and Heat Transfer in Medium Speed Diesel Engine Tampere 2005 Tampereen teknillinen yliopisto Julkaisu 562 Tampere University of Technology Publication 562 Pertti Taskinen Modelling of Spray Combustion, Emission Formation and Heat Transfer in Medium Speed Diesel Engine Thesis for the degree of Doctor of Technology to be presented with due permission for public examination and criticism in Konetalo Building, Auditorium K1702, at Tampere University of Technology, on the 2nd of December 2005, at 12 noon Tampereen teknillinen yliopisto - Tampere University of Technology Tampere 2005 ISBN 952-15-1476-0 (printed) ISBN 952-15-1498-1 (PDF) ISSN 1459-2045 i ABSTRACT This thesis deals with the spray combustion, emissions (NOx and soot) formation and heat transfer theories of phenomena and their modelling related to medium speed diesel engines The modelling work was done with the Marintek A/S version of the open source code KIVA-II program by implementing new sub-models or by modifying old models of the phenomena into the code The aim of the work has been to develop a simulation tool for medium speed diesel engines that can be applied later in the optimisation process of the engine economy with the allowed pollution level by computing different cases with the different engine parameters such as compression ratio, fuel injection timing, injection rate shaping, direction of injection, diameter of the nozzle hole etc In developing work of the KIVA-II code main attention was focused on the following phenomena: the drop vaporisation under a high-pressure environment, the soot formation modelling by the Hiroyasu TM models and the or the oxidation by the NSC model, the soot radiation modelling by the simplified model (pure emission) or the DOM, the convective heat transfer modelling and the spray turbulence modelling by the RNG/STD k-e turbulence models The high pressure drop vaporisation model was developed based on the equality of the fugacity of the fuel in liquid and the vapour phase on the drop surface The mass fraction of fuel vapour in the drop surface is much larger with the high pressure model than with the original low-pressure model yielding a more realistic ignition of the fuel vapour and air mixture and the combustion The original TM soot formation model of the code was a failure and this was rectified The Hiroyasu soot formation and the NSC soot oxidation model were added into the code and formulated into the source term form using either the computational cell average or the EDCweighted values of the cell quantities in the soot transport equation The soot emissions after modifications were a more realistic level than in the case of the original formulation and the models Also the lack of an NSC soot oxidation model able to predict the soot oxidation rate correctly was taken into account by the extra constant in the model The soot radiation was taken into account in the internal energy transport equation by the simplified model (optically thin radiant media), i.e pure emission from the radiant media or the RTE solved by the DOM The radiant heat flux to piston top becomes the more realistic level with the DOM than with the simplified model compared to the experimental values of the slightly other type diesel ii engine than the modelled medium speed diesel engine This shows that the absorption of soot radiation in the radiant region must also be taken into consideration Effect of the soot radiation on temperature of the gas appears only in the soot region, not in the fuel vapour reaction zone where the soot is not found Therefore the soot radiation does not reduce maximum temperatures of the gas in the fuel vapour reaction zone or in the nitrogen oxide (NOx) formation regions near the reaction zone and so influence in the NOx emissions from the engine The original temperature wall function of the KIVA-II based on the modified Reynolds analogy under-predicts the heat flux to wall considerably The model was replaced by the model which was based on the use of a one-dimensional energy equation and the correlation of dimensionless temperature including an increasing turbulent Prandtl number near the wall The heat flux to piston top with the new model was a more realistic level than with the original model of the code compared to the experimental values of the other type diesel engine The modified RNG k-epsilon model was developed based on the results obtained with the STD and the basic RNG k-e models According to the results mentioned above the STD model is too diffusive while the basic RNG is too less diffusive in the high rate of the strain region (spray region) and therefore the fuel vapour mixing (combustion) occurs in an un-satisfactorily way In the turbulence model developed the additional term of the epsilon equation was modified suitably and therefore the spray spreading and the combustion occur more realistically compared to either the basic RNG or the STD k-e turbulence model cases The gas turbulence intensity was reduced in the early phase of combustion and emphasized in the later phase of combustion compared to the situation with the STD model The cylinder pressure curve becomes by far the closest with the new turbulence model than either of both the models mentioned above In the work the failure of the basic RNG turbulence model of the KIVA-3V was found and rectified iii PREFACE This work has been carried out at the Institute of Energy and Process Engineering, Tampere University of Technology (TUT) The work has been funded by the PROMOTOR program (Mastering the Diesel Process (MDP)) of the National Technology Agency of Finland (Tekes) and the CFD Graduate school program of the Aerodynamic Laboratory of Helsinki University of Technology (HUT) I wish to express my gratitude to Professor Reijo Karvinen, advisor of my dissertation for his guidance during this work I would also like to thank all the staff at the Institute of Energy and Process Engineering Furthermore, I wish to extend my thanks to Dr Eilif Pedersen at the Marintek A/S Research Centre of the Sintef Group, Trondheim, Norway for his unique guidance with the KIVA-II code and to Professor Martti Larmi at the Internal Combustion Engine Laboratory (ICEL) of Helsinki University of Technology for the discussions and meetings on the MDP project I would also like to thank Mr Gösta Liljenfeldt at the Wartsila Diesel Company in Vaasa for the support during the entire co-operation time of the medium speed diesel engine process modelling and Mr James Rowland for the high quality reviewing the English of the manuscript Finally, I must thank to my roommate Licentiate of Technology Vesa Wallen, for the interesting and inspiring discussions on the work Tampere, May 2005 Pertti Taskinen iv v CONTENTS ABSTRACT i PREFACE iii CONTENTS v NOMENCLATURE ix INTRODUCTION 1.1 General aspects 1.2 Diesel process modelling 1.3 Goal and outline of this thesis THEORY OF DIESEL PROCESS MODELLING 2.1 Governing field equations 2.2 Main sub-models in diesel process modelling 2.2.1 Turbulence modelling 2.2.2 Fuel spray modelling 12 2.2.2.1 General aspects 12 2.2.2.2 Fuel jet break-up/atomisation regimes 13 2.2.2.3 Short review of the fuel spray models 15 2.2.3 Drop dynamics 21 2.2.4 Drop vaporisation 23 2.2.5 Fuel vapour combustion 27 2.2.5.1 General aspects 27 2.2.5.2 Premixed combustion 29 2.2.5.3 Diffusion combustion 30 2.2.6 Emissions modelling 39 2.2.6.1 Nitrogen oxide emissions 40 2.2.6.2 Soot emissions 41 2.2.6.2.1 Soot formation 41 2.2.6.2.2 Soot oxidation 45 2.2.6.3 Soot modelling by EDC-model formulation 47 vi 2.2.7 Heat transfer 49 2.2.7.1 Convective heat transfer 49 2.2.7.2 Heat transfer by radiation 51 AUTHOR’S IMPLEMENTED/DEVELOPED SUBMODELS AND THEIR CONTRIBUTION TO THE MODELLING TOOL FOR DIESEL PROCESS ANALYSIS 57 3.1 Sub-models in baseline Marintek KIVA-II 57 3.2 Sub-models used in current KIVA-II 57 3.3 List of author’s publications related to this work 59 MODELLING RESULTS AND THEIR EXPERIMENTAL VERIFICATION 4.1 Turbulence results with the STD, basic RNG and modified RNG k-e models 61 61 4.1.1 Turbulence intensity 61 4.1.2 Turbulence kinetic energy distribution 64 4.1.3 Turbulence viscosity 66 4.1.4 Spray spreading 67 4.2 Results of drops high/low-pressure vaporisation formulation 69 4.2.1 Amount of fuel vapour in combustion chamber 70 4.2.2 Pressure of cylinder gas 71 4.2.3 Cumulative heat release 71 4.3 Effect of turbulence model on combustion results 72 4.3.1 Pressure of cylinder gas 73 4.3.2 Cumulative heat release 74 4.3.3 Temperature of gas 75 4.4 Nitrogen oxide emissions 78 4.5 Soot emissions 82 4.6 Heat transfer 88 CONCLUSIONS 93 REFERENCES 97 96 97 REFERENCES Abraham, J., and Magi, V (1997a):”Computations of Transient Jets: RNG k-e Model Versus Standard k-e Model”, SAE Technical paper 970885 Abraham, J., and Magi, V (1997b): Application of the Discrete Ordinates Method to Compute Radiant Heat Loss in a Diesel Engine, Numerical Heat Transfer, Part A, 31:597-610 Abramzon, B., and Sirignano, W A (1989): “Droplet Vaporization Model for Spray Combustion Calculations”, Int J Heat Mass Transfer 32(9), pp.1605-1618 Amsden, A A., O' Rourke, P J., and Butler, T D (1989): "KIVA-II: A Computer Program for 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S., Gatski, T B and Speziale C G (1992): Development of Turbulence Models for Shear Flows by a Double Expansion Technique Phys Fluid A, 4, 1510 Yan, J D., and Borman, G L (1988): Analysis and in-cylinder measurement of particulate radiant emissions and temperature in a direct injection diesel engine, SAE technical paper 881315 103 Younis, B (1997): Lecture Notes for Course on Applied Turbulence Modelling, Helsinki University of Technology, 19-25 May APPENDIX A Modelled engine specifications: Details of the modelled Wärtsilä W46 medium speed diesel engine are listed in Table A1 Cylinder bore 460 mm Stroke 580 mm Compression ratio 14.0 Running speed 500.0 rpm Number & size of nozzle holes 10 x 0.78 mm Start of injection 10.deg BTDC Fuel injection duration 26.5 deg Total injected fuel mass/cycle 12.3 g Fuel Heavy fuel (Neste Mastera) Start of ignition 7.0deg BTDC Simulation begins 40.deg BTDC Air temperature at 20 deg BTDC 654.0 K Air pressure at 40 deg BTDC 33.5 bar Swirl ratio 0.2 Table A1 Initial conditions and operating/construction parameters of the modelled diesel engine Computational mesh of modelled engine The computational mesh consists of 45 non-equally spaced cells in the radial, 21 in the azimuthally and 46 equally spaced cells in the axial direction Due to piston travel the minimum number of cells at TDC is 17 The rate change of length of cell in the radial direction is about % The angle of the computational sector is 36 degrees The grid is shown in Fig A1 Figure A1 Computational grid of modelled engine at TDC APPENDIX B Flow chart of the updated KIVA-II modelling tool: Figure B1 Flow chart of the KIVA-II modelling code Tampereen teknillinen yliopisto PL 527 33101 Tampere Tampere University of Technology P.O Box 527 FIN-33101 Tampere, Finland ... average n At time step n Comb Combustion Htr Heat transfer Liq Liquid Spray Interaction with the spray Vap Vapour Acronyms AS Abramzon and Sirignano CHTC Characteristic time combustion model CL Cliffe-Lever... diesel engines can nowadays be done by a sophisticated numerical simulation tool and/or experimentally The numerical simulation of the spray combustion process of a medium speed diesel engine. .. µ ∂Y ρ u Yl = − t Sct ∂xi ' i ' (8) ~ ~ ~ The source terms S mSpray , S USpray and S ISpray in Equations (1), (2) and (3) due to spray have been j ~ ~ described in KIVA-II manual (Amsden et al.,