Modelling of soot formation and aromatic growth in laminar flames and reactor systems

387 Pages·2015·7.28 MB·English

by  Bjorn Waldheim

Imperial College London
Department of Mechanical Engineering
Modelling of soot formation and
aromatic growth in laminar flames
and reactor systems
Civilingenjo¨r Bj¨orn Bengt Olof Waldheim
April 13, 2015
Supervised by Prof. Peter Lindstedt
Submitted in part fulfilment of the requirements for the degree of
Doctor of Philosophy in Mechanical Engineering of Imperial College
London
and the Diploma of Imperial College London
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Declaration
I certify that all material in this thesis which is not my work have been
properly acknowledged.
Bj¨orn Bengt Olof Waldheim
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Abstract
Soot particles formed and emitted from (e.g.) direct-injected diesel engines
aredangeroustohumanhealthandlegislativemeasuresusedtoreduceemis-
sionsposeatechnicalchallengeformanufacturers. Modelsofsootformation
and oxidation may therefore be useful tools for developing engines and con-
trolstrategies. Inthepresentwork,asectionalsootmodelabletoreproduce
thesootparticlesizedistribution(PSD)isappliedtolaminarpremixedand
di↵usion flames as well as a reactor system. The soot PSDs in laminar
premixed stagnation flow flames were found to be sensitive to the coagula-
tion collision e�ciency and a novel model was developed. The soot model
under-predictedsootvolumefractionlevelswhenappliedtoasetoflaminar
ethylene and propane counter-flow di↵usion flames and a sensitivity anal-
ysis suggested further assessment of the formation of poly-cyclic aromatic
hydrocarbons (PAH) was needed. The chemical reaction mechanism was
subsequently assessed using species measurements from a laminar premixed
benzene flame and selected parts of the reaction mechanism reviewed. Rea-
sonableagreementwasobtained,includingforformationofPAHs. However,
non-existing or insu�cient oxidation paths of some PAH species, including
pyrene, may contribute to over-predictions by the soot model during non-
sooting conditions. Formation of PAHs in a laminar ethylene counter-flow
di↵usion flame was investigated next. The agreement between calculations
and measurements was found to be reasonable for major, minor and single
ring aromatic species. However, the calculated concentrations of all PAH
species are under-predicted. The under-prediction of pyrene is comparable
to the under-prediction of the soot volume fraction in some of the di↵usion
flames previously investigated, making the uncertainty of the PAH chem-
istryapossibleexplanation. Futuresootmodellingresearchshouldtherefore
focus on investigating the PAH chemistry for di↵erent types of flames and
fuels.
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Acknowledgment
I am very grateful for and have enjoyed the guidance, support and su-
pervision of Prof. Peter Lindstedt. The co-supervision by Dr. Rolf Egnell
and Dr. Ola Stenl˚a˚as have also been a pleasure. I am a also very grate-
ful to Scania CV AB and the Swedish Energy Agency for their financial
support making this research possible. I would like to personally thank
Madelaine Nordqvist,Dr. Jonas Holmborn,Per St˚alhammar,Per Langeand
Dr. Raymond Reinmann at Scania CV AB for their support. The support
regarding calculations of thermodynamic data received from
Dr. Roger Robinson at Imperial College is gratefully acknowledged. The
management of references for the reaction mechanism by Peter Kraus,
Dr. Valentini Markaki and Dr. Mark Lee Potter have been of great help
and have been used in the current work. The structures of species drawn
by Dr. Valentini Markaki have also been used in the current work and is
gratefully acknowledged. I am grateful for the support and supervision
from Prof. Bengt Johansson, Prof. Xue-Song Bai, Prof. O¨vind Andersson
and Dr. Joakim Pagel at Lund University during my visit there. I wish
all luck to all present and former collueagues at Imperial College that I had
the pleasure to get to know and become friends with. I would also like to
thank all present and former colleagues at Scania CV AB for their interest
in my research and interesting discussions regarding mechanical engineer-
ing. I am grateful to colleagues and friends at Lund University for their
help regarding all kinds of matters.
My beloved parents Lars and Eva Waldheim have always encouraged my
curiosity and learning and together with my sisters
Ingrid and Johanna Waldheim and relatives have always stood by my side.
I also like to thank my friends in or from Stockholm, especially to those
I grew up with in S¨atra, for there appreciation and all the great times we
have had so far.
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