Experimental and Numerical Study of Dynamics of Premixed Hydrogen-Air Flames Propagating in Ducts

162 Pages·2016·6.094 MB·English

by  Dr. Huahua Xiao (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Huahua Xiao

Experimental and
Numerical Study of
Dynamics of Premixed
Hydrogen-Air Flames
Propagating in Ducts
Springer Theses
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Huahua Xiao
Experimental and Numerical
Study of Dynamics
of Premixed Hydrogen-Air
Flames Propagating in Ducts
Doctoral Thesis accepted by
University of Science and Technology of China,
Hefei, China
123
Author Supervisor
Dr. Huahua Xiao Prof. Jinhua Sun
State Key Laboratoryof Fire Science University of Science andTechnology
University of Science andTechnology ofChina
ofChina Hefei
Hefei China
China
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-662-48377-0 ISBN978-3-662-48379-4 (eBook)
DOI 10.1007/978-3-662-48379-4
LibraryofCongressControlNumber:2015949445
SpringerHeidelbergNewYorkDordrechtLondon
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Parts of this thesis have been published in the following articles:
Xiao H, Sun J, Chen P (2014) Experimental and numerical study of premixed
hydrogen/air flame propagating in a combustion chamber. J Hazard Mater
268:132–139 (Reproduced with Permission).
XiaoH,WangQ,ShenX,AnW,DuanQ,SunJ(2014)Anexperimentalstudyof
premixed hydrogen/air flame propagation in a partially open duct. Int J Hydrogen
Energy 39:6233–6241 (Reproduced with Permission).
Xiao H, He X, Duan Q, Luo X, Sun J (2014) An investigation of premixed
flame propagation in a closed combustion duct with a 90° bend. Appl Energy
134:248–256.
XiaoH,WangQ,ShenX,GuoS,SunJ(2013)Anexperimentalstudyofdistorted
tulip flame formation in a closed duct. Combust Flame 160:1725–1728
(Reproduced with Permission).
XiaoH,AnW,DuanQ,SunJ(2013)Dynamicsofpremixedhydrogen/airflamein
a closed combustion vessel. Int J Hydrogen Energy 38:12856–12864 (Reproduced
with Permission).
Xiao H, He X, Wang Q, Sun Q (2013) Experimental and numerical study of
premixed flame propagation in a closed duct with a 90° curved section. Int J Heat
Mass Transfer 66:818–822.
Xiao H, Makarov D, Sun J, Molkov V (2012) Experimental and numerical
investigation of premixed flame propagation with distorted tulip shape in a closed
duct. Combust Flame 159:1523–1538 (Reproduced with Permission).
Xiao H, Shen X, Sun J (2012) Experimental study and three-dimensional simula-
tion of premixed hydrogen/air flame propagation in a closed duct. Int J Hydrogen
Energy 37:11466–11473 (Reproduced with Permission).
Xiao H, Wang Q, He X, Sun J (2011) Experimental study on the behaviors and
shape changes of premixed hydrogen-air flames propagating in horizontal duct.
Int J Hydrogen Energy 36:6325–6336 (Reproduced with Permission).
XiaoH,WangQ,SunJ,HeX,YaoL(2010)Experimentalandnumericalstudyon
premixed hydrogen/air flame propagation in a horizontal rectangular closed duct.
Int J Hydrogen Energy 35:1367–1376 (Reproduced with Permission).
’
Supervisor s Foreword
Understanding of the dynamics of premixed flames evolving in tubes is of great
importance in a broad range of practical combustion phenomena of scientific and
engineering interest, such as gas explosions in confined regions, and burning
processesininternalcombustionengines.Atransientpremixedflameinatubeisan
extremely complex, dynamic process involving chemical kinetics, heat and mass
transfer, and fluid dynamics. The complexity of the flame dynamics presents
enormous challenges which combustion scientists and engineers have to face.
Greatinterestinnewalternativefuelsisgeneratedassociatedwitheconomicand
environmental concerns in the use of fossil fuels, e.g., high fuel price, global
warming and environmental pollution. Hydrogen asan energy carrieris one ofthe
promising alternative fuels because of its potentially high efficiency and ultra-low
harmful emissions. However, there are serious problems to overcome when using
hydrogen as an energy carrier. The major issues in relation to combustion and
safety are the unique characteristics of hydrogen due to its high diffusivity and
reactivity, which can lead to leak, fire, and explosion hazards.
In the past eight years, Dr. Huahua Xiao has been devoted to premixed flame
propagation in confined regions. In the present work, dynamics of premixed
hydrogen–air flames propagating in ducts under a large variety of conditions are
experimentally and numerically studied. A subsequent theoretical analysis is per-
formed. Numerical methods and combustion models are suggested and validated
against experimental and theoretical results. Important knowledge of premixed
flame dynamics and combustion modeling is presented. Particularly, one out-
standing finding proposed by Dr. Xiao is the “distorted tulip flame”. Furthermore,
the interactions between the flames and various physical phenomena, e.g., the
combustion-generated flow, pressure wave and boundary layer, are examined to
elucidate the underlying mechanisms that control the combustion processes.
vii
viii Supervisor’sForeword
Overall, this work provides us with important new insights and deeper under-
standingofpremixedflamedynamics,andcombustionofhydrogen–airpremixtures
in ducts.
Hefei Prof. Jinhua Sun
July 2015
Abstract
Premixed combustion of chemically reactive gas mixture is a very fundamental
subject for a broad range of issues of scientific and engineering interest, e.g.,
accidental explosions and propulsion applications. The fundamental understanding
ofpremixedflamepropagationphenomenaisessentialforthedevelopmentofnovel
analyticalandnumericalcombustionmodels.Premixedflamedynamicsinconfined
vessels is of particular importance since it provides understanding of the burning
processestakingplaceininternalcombustionengines,andexplainsthemechanisms
behindflameaccelerationthatcanleadtotransitionfromdeflagrationtodetonation.
Inaddition,hydrogenisapromisingalternativeenergycarrierinthefuture,anditis
of great importance to characterize the combustion behavior of its blends with air.
Meantime,thedevelopmentandthevalidationofcontemporarycombustionmodels
ofwide applicabilityareimportant for both hydrogen combustionapplicationsand
explosion safety.
This study aims to provide fundamental and in-depth investigation of premixed
combustion and reliable prediction approaches for hydrogen combustion and
explosioninair.Twoprimaryaimsareplannedtobeachievedinthepresentwork.
The first objective is to study the premixed combustion dynamics in tubes, i.e.,
flame propagation and pressure build-up, and explain the mechanisms underlying
the dynamics of the premixed flame. Another important target of this study is to
investigate hydrogen gas explosions in tubes, and to develop and validate theo-
retical and numerical methods that could provide reasonable prediction of acci-
dental gas explosions inside tubes. Laboratory experiments and CFD numerical
simulations of premixed hydrogen–air flames in tubes are the basis of the thesis.
In the experiments, both the dynamics of premixed hydrogen–air flame propa-
gation and pressure build-up in half-open and closed horizontal ducts at various
equivalence ratios are investigated using high-speed schlieren photography and
pressurerecords.Thehigh-speedschlierendeviceisusedtorecordthechangesboth
intheflameshapeandpositionasafunctionoftimeduringthecombustionprocess.
The pressure transient in the duct during the nonsteady combustion is measured
usingapressuretransducer.Theinfluencesofgravity,openingratio,andequivalence
ratioontheflamedynamicsarealsoexaminedintheexperimentalinvestigation.
ix
x Abstract
In the numerical simulations, the premixed combustion wave is simulated as a
two-dimensional (2D) or three-dimensional (3D) chemically reacting flow.
Adynamicthickenedflame(TF)modelisemployedinthe2Dnumericalsimulation
toaccountforthepremixedcombustion.Thechemicalreactionofhydrogenandair
istakenintoaccountusinga19-stepdetailedchemistryscheme.The3Dnumerical
simulations are carried out using two numerical approaches. The first one is based
on the same combustion modeling technique as that in the 2D simulation, namely
thedynamicTFmethod.Thedifferenceinthe3Dcalculationsisthatadynamically
and locally adaptive mesh refinement is adopted, and tracks the location of the
flame front. Besides, the hydrogen–air chemical reactions are taken into account
using a seven-step chemistry scheme. The second one is a large eddy simulation
(LES) approach together with a turbulent burning velocity model. The LES pre-
mixed combustion model is applied to gain an insight into various phenomena of
flameandexplaintheexperimentalobservations.Themodelaccountsfortheeffects
offourdifferentphysicalmechanisms,i.e.,flowturbulence,turbulencegeneratedby
flame front itself, diffusive-thermal instability, and transient pressure and temper-
ature of unburned gas on the burning velocity.
The experiments show that premixed hydrogen–air flames propagating in ducts
undergo more complex shape changes and exhibit more distinct characteristics
comparedtothoseofothercommongaseousfuels.Oneoftheoutstandingfindings
is that significant distortions happen to classical tulip flame front after its full
formationwhenequivalenceratiorangesfrom0.84to4.22intheclosedduct.This
interestingphenomenonisnamedas“distortedtulipflame”.Adistortedtulipflame
is initiated as the distortions or indentations are created very near the leading tips
of the tulip lips after a well-pronounced classical tulip flame is produced. The
distorted tulip flame develops into a salient “triple tulip” shape as the secondary
tulip cusps approach the center of the primary tulip lips and appear comparable to
the primary cusp. A second distorted tulip flame appears with a cascade of
secondary cusps on the primary tulip lips just before the collapse of the first one.
The tulip flame distortions are specially scrutinized and distinguished from the
classical tulip. The dynamics of a distorted tulip flame is different from that of a
classical tulip flame. The distorted tulip flame experiences more complex shape
changes and more unstable combustion process than the classical tulip flame. The
normal tulip flame can be reproduced after the disappearance of the first distortion
followedbyanotherdistortion.Theschlierenimagesandthepressurerecordsshow
that the distorted tulip flame propagation can be divided into five stages of
dynamics,i.e.,sphericalflame,finger-shapeflame,flamewithitsskirttouchingthe
sidewalls, tulip flame, and distorted tulip flame. The initiation of flame shape
changescoincideswiththedecelerationbothofpressureriseandflamefrontspeed
forflameswithtulipdistortions.Andtheformationanddynamicsofbothtulipand
distortedtulip flamesdepend onthemixturecomposition. Gravityhasanoticeable
impacton thetulip flame and can lead the tulip flame tocollapsein different ways
between low and high equivalence ratios. The opening ratio can significantly
influence the flame dynamics in a partially open duct. When the opening ratio is
smaller than 0.4, a remarkable distorted tulip flame can be formed. The