Modeling of injection-rate shaping in diesel engine combustion [Elektronische Ressource] / vorgelegt von Vivak Luckhchoura

Vivak Luckhchoura

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2010
• Nombre de lectures: 27
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Modeling of Injection-Rate Shaping
in Diesel Engine Combustion
Vivak LuckhchouraModeling of Injection-Rate Shaping
in Diesel Engine Combustion
Von der Fakult¨at fu¨r Maschinenwesen der
Rheinisch-Westf¨alischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades eines Doktors der
Ingenieurwissenschaften genehmigte Dissertation
vorgelegt von
Vivak Luckhchoura
Berichter: Univ.-Prof. Dr.-Ing. Dr. h.c. Dr.-Ing. E.h. N. Peters
Univ.-Prof. Dr.-Ing. (USA) S. Pischinger
Tag der mu¨ndlichen Pru¨fung: 07. Juli 2010
Diese Dissertation ist auf den Internetseiten
der Hochschulbibliothek online verfu¨gbar.Acknowledgements
This dissertation is the outcome of my work at the Institute for Combustion Tech-
nology of the RWTH Aachen University in Germany.
First and foremost I owe my deepest gratitude to my supervisor, Prof. Norbert
Peters, who supported, encouraged and guided me throughout my thesis. He
allowed me freedom to work on my own way, and he always found time for my
questions. He has been a source of inspiration to my work.
I am heartily thankful to Prof. Stefan Pischinger for his interest in my work and
being the co-examiner of my doctoral examination committee, and to Prof. Andr´e
Bardow for serving as chair of my doctoral examination committee.
IamgratefultoGeneralMotors(GM)Companyforprovidingthefinancialsupport
within the framework of the Collaborative Research Laboratory (CRL) which is
collaboration between GM and RWTH Aachen University. It was a great pleasure
to work with the people from the Powertrain Systems Research Laboratory of
the GM R&D Center in Warren in Michigan, who were always ready to help
and support my research work. Especially, I am indebted to Dr. Ramachandra
Diwakar for many fruitful discussions and his critical comments on my work. I
would also like to thank my colleagues in the CRL from the University for their
wonderful cooperation. A special thanks goes to Mr. Michael Rottmann from the
Institute of Combustion Engines of the RWTH Aachen University for providing
the experimental data.
MysincerethankstoFranc¸ois-XavierRobert,AbhinavSharma,ChristopherKupiek,
Aitor Chivite and Rahul Pardeshi for supporting my research work through their
Mini or Master thesis.
I would like to extend my thanks to all my current and former colleagues from my
institute for their kind supports and the great time. Especially, I thank to Stefan
Vogel, Frank Freikamp, Jost Weber, Sylvie Honnet, Christian Felsch, Olaf R¨ohl,
Jens Henrik G¨obbert, Rainer Dahms, Michael Gauding, Bernhard Jochim, Hyun
Woo Won and Anyelo Vanegas.
vI owe a lot to Gu¨nter Paczko, with whom I not only enjoyed my lunch breaks and
discussions abouteverything, buthealsocontributed inmanywaystomyresearch
work. His way of thinking has left a permanent impression on me. I would also
like to thank him and Sonja Engels for their readiness and patience in correcting
my German grammar mistakes.
I thank my parents for educating me, for their unconditional support and encour-
aging me to follow my own path. Thanks to my sister and brother for their love
and care.
To Ewelina Sobierska goes the greatest “thank you” for believing in me and her
continuing support. She has been a constant reminder to me that there are other
more important things in life, through her I learnt to have joy in small things and
she took care that I do not work on weekends.
viContents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Purpose of the Research . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Outline of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Literature Survey 5
2.1 Combustion in Direct Injection Diesel Engines . . . . . . . . . . . . 5
2.2 Studies of Injection-Rate Shaping . . . . . . . . . . . . . . . . . . . 7
3 Description of Turbulent Flow and Mixing Field 13
3.1 Gas Phase Governing Equations . . . . . . . . . . . . . . . . . . . . 13
3.2 Turbulent Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.1 Scales of Turbulent Motion . . . . . . . . . . . . . . . . . . . 15
3.2.2 Averaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.3 Turbulent Flow and Mixing Field . . . . . . . . . . . . . . . 17
3.3 CFD Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4 Liquid Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 Combustion Model 25
4.1 Laminar Flamelet Concept . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.1 Definition of the Mixture Fraction . . . . . . . . . . . . . . . 26
4.1.2 Flamelet Equations . . . . . . . . . . . . . . . . . . . . . . . 28
4.2 The Preassumed Shape PDF Approach . . . . . . . . . . . . . . . . 32
4.3 RIF Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.4 Chemical Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.5 Flamelet Approach to Soot Modeling . . . . . . . . . . . . . . . . . 35
4.6 Alternative Flamelet Equations for Soot Moments . . . . . . . . . . 38
4.7 Transport Equation for Soot Moments in Physical Space . . . . . . 39
5 Pollutant Formation 41
5.1 Soot Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.1.1 Formation of Benzene . . . . . . . . . . . . . . . . . . . . . 41
5.1.2 Growth of PAHs . . . . . . . . . . . . . . . . . . . . . . . . 43
5.1.3 Formation, Growth and Oxidation of Soot Particles . . . . . 44
viiContents
5.2 NO Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54x
6 Effect of Physical Parameters on Soot Formation 57
6.1 Scalar Dissipation Rate . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2 Oxidizer Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.3 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7 Experimental and Numerical Setup 63
7.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.1.1 Injection System . . . . . . . . . . . . . . . . . . . . . . . . 64
7.2 Numerical Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7.3 Post-Processing Methods . . . . . . . . . . . . . . . . . . . . . . . . 67
8 Characterization of the Baseline Rate Shapes 71
8.1 Flow and Mixing Field . . . . . . . . . . . . . . . . . . . . . . . . . 73
8.2 Global Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
8.3 Detailed Analysis of Soot Formation and Oxidation . . . . . . . . . 80
8.4 Two-Part Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
8.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
9 Transient Effect of the Boot-Shaped Injection Rates 87
9.1 Multiple-Flamelet Model . . . . . . . . . . . . . . . . . . . . . . . . 88
9.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 91
9.2.1 Effect of the Oxidizer Temperature and the Scalar Dissipa-
tion Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
9.2.2 Comparison of the RIF Model with the M-RIF Model . . . . 93
9.2.3 Transient Effect of the Rate Shapes . . . . . . . . . . . . . . 96
9.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
10 Effect of Soot Modeling Approaches 111
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
10.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 112
10.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
11 Summary 117
Bibliography 119
Appendix A PSDF from Moments 129
Appendix B Calculation of Knudsen number 131
viiiContents
Appendix C Abbreviations 133
ix1 Introduction
1.1 Motivation
Lowest emissions with highest engine performance: namely, power output, low
noise levels, low fuel consumption and low engine-out emissions are the targets for
the success of future diesel engines. Highly refined and robust technical advance-
ments are required to meet the above targets. Solutions leading to these technical
advancements are of particular interest. Moreover, engine development strategies
leading to the low engine-out raw emissions are attractive with respect to keeping
the costs low for exhaust gas after-treatments.
Theinjectionsystem, theexhaustgasrecirculation(EGR)rate,thecompression
ratio, the shape of the combustion chamber, the air motion, the new exhaust gas
after-treatment techniques, the intake boost pressure are some of the important
measures to improve the combustion process and to achieve a significant reduction
of engine raw emissions. Besides these measures, a systematic control of mix-
ture formation could enable considerable improvements in mixture formation and
combustion process (and engine-out emissions). In this regard, the capability and
the flexibility of injection-rate shaping are important, which results in a specific
temporal distribution of fuel for a given injection duration. Thus, a multitude of
injectionrateshapesarepossiblebesidestheconventionaltop-hatshape. Itiswell-
known from the literature that, a low rate at the beginning of injection and a high
rate at the end of injection lead to a relatively lower fuel quantity at the premixed
combustion phase (lower combustion noise) and a high spray energy near the e