51-Varghese K George-CFD Simulation of Hydrogen Combustion-4

8/13/2019 51-Varghese K George-CFD Simulation of Hydrogen Combustion-4

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CFD SIMULATION OF HYDROGENCOMBUSTION

CHAPTER 1

INTRODUCTION

Over the past three decades there has been considerable effort in the world to develop andintrod ce alternative transportation f els to replace conventional f els s ch as !asolineand diesel" environ#ental iss es" #ost notabl$ air poll tion and li#ited availabilit$ ofconventional f els are a#on! the principle drivin! forces behind this #ove#ent%

If one tries to find for the definition of perfect f el" h$dro!en probabl$ satisfies #ost ofthe desirable characteristics of s ch a f el% Plentif l and clean b rnin!" h$dro!en has ver$hi!h ener!$ content%

D e to diffic lties in cond ctin! spatiall$ resolved #eas re#ents of co#b stioncharacteristics in devices" the n #erical si# lation can be cost effective approach tost d$ the co#b stion #echanis#% In this wor&" Co#p tational 'l id D$na#ics (C'D) based n #erical si# lations have

been perfor#ed to st d$ the co#b stion of non*pre#i+ed h$dro!en*air #i+t re inc$lindrical cha#ber%

The perfor#ance of the co#b stor is eval ated b$ sin! C'D pac&a!e ',UENT -%.nder adiabatic wall condition at vario s e/ ivalence ratios and #ass flow rates ofh$dro!en 0 air%

1%1 Ob ectives and 2cope

The ob ective of this wor& is to st d$ the f nda#entals of Co#p tational 'l id D$na#ics(C'D)" N #erical #odelin!" co#b stion pheno#enon and vario s aspects in order to sethe# for solvin! the realistic proble#s% The ob ectives of this research effort are3

The nderstandin! of the basics of H$dro!en*o+$!en reaction #echanis#" itsco#b stion and the !eo#etr$ of the c$lindrical cha#ber sed in this st d$ is ver$i#portant for si# latin! h$dro!en*air co#b stion s$ste#%

To develop a two di#ensional n #erical #esh and flow #odel which ade/ atel$and acc ratel$ represent the ph$sical #odel of co#b stion cha#ber and is si#ple

eno !h to li#it the a#o nt of co#p tational ti#e for obtainin! a sol tion% To prepare a #athe#atical #odel for h$dro!en*air co#b stion s$ste#% The ob ective of this st d$ is to find and appl$ appropriate #odel that i#prove the

si# lation of co#b stion with the co##ercial C'D*pac&a!e ',UENT%

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4enerate n #erical data6sol tions which correlate as # ch as possible with thee+peri#ental data for vario s conditions incl din! e/ ivalence ratios" #ass flowrates of h$dro!en*air #i+t re%

The #ain ob ective of the research presented in this se#inar" is the develop#ent of an #erical infrastr ct re for the # ltidi#ensional n #erical si# lation of co#b stion

processes with the #a+i# # level of acc rac$%

CHAPTER 7

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H8DRO4EN A2 A 'UE,

'i! re 13 Periodic Table

H$dro!en is a colorless" odorless" tasteless" and nonpoisono s !as nder nor#alconditions on Earth% It t$picall$ e+ists as a diato#ic #olec le% H$dro!en is the #ostab ndant ele#ent in the niverse" acco ntin! for 9. percent of the niverse b$ wei!ht%However" it is not co##onl$ fo nd in its p re for#%

7%1 Properties of H$dro!en as a f el

H$dro!en has several i#portant che#ical properties that affect its se as a f el3 It readil$ co#bines with o+$!en to for# water" which is absol tel$ necessar$ for

life on this planet% It has a hi!h*ener!$ content per wei!ht (nearl$ : ti#es as # ch as !asoline)" b t

the ener!$ densit$ per vol #e is / ite low at standard te#perat re and press re%;ol #etric ener!$ densit$ can be increased b$ storin! the h$dro!en nderincreased press re or storin! it at e+tre#el$ low te#perat res as a li/ id%H$dro!en can also be adsorbed into #etal h$drides%

H$dro!en is hi!hl$ fla##able< it onl$ ta&es a s#all a#o nt of ener!$ to i!nite itand #a&e it b rn% It also has a wide fla##abilit$ ran!e" #eanin! it can b rn whenit #a&es p = to >= percent of the air b$ vol #e%

H$dro!en b rns with a pale*bl e" al#ost*invisible fla#e" #a&in! h$dro!en firesdiffic lt to see%

The co#b stion of h$dro!en does not prod ce carbon dio+ide (CO 7)" partic late"or s lf r e#issions% It can prod ce nitro s o+ide (NO ? ) e#issions nder so#econditions%

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H$dro!en can be prod ced fro# renewable reso rces" s ch as b$ refor#in!ethanol (this process e#its so#e carbon dio+ide) and b$ the electrol$sis of water(electrol$sis is ver$ e+pensive)%

Ener!$ Content for 1 &! (7%7 lb) of H$dro!en @ =7= 2tandard C bic 'eet(Reactin! with o+$!en to for# water)%

Hi!her Heatin! ;al e ,ower Heatin! ;al e1=1"-.. B 119"-.. B

Table 13 Heatin! ;al es of H 7

Properties of H$dro!en as a f el

The properties of h$dro!en are listed in table 7% alon! with conventional f elsi%e%4asoline 0 Diesel and other alternative f els s ch as CN4" ,P4" and io!as%

Properties CN4 H$dro!en 4asoline ,P4 io!as

,ower Heatin! ;al e( B6 !)

.... 17... =7... =-... ...

Densit$ ( !6# : ) .%-9 .%.9 >7.*> . 7%7= 1%1

'la#e 2peed (c#6sec) :=%. 7- *:7 : %7 7 %.

2toichio#etric A6'( !6 !)

1>%: :=%: 1=%- 1 % -

'la##abilit$ li#it (Fvol of air)

%:*1 =*> 1%=*>%- 7%1 *9%- >% *1=

Octane No% 1:. 1:.G -*9= 1.:*1. 17.

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A to I!nition Te#p%(. C)

>:. 777 =7 >..

,atent Heat of;apori ations( B6# : )

.9 :> =7 =9:* =9

5olec lar ei!ht 1 % *1>%. 1.. *-.

2pecific 4ravit$ .%=7= .%.> .%>7*.%>

oilin! Te#p% (') *7 9 *=7: .*=:>

Table 73 Properties of f els

7%1%1 ,i#its of 'la##abilit$

The li#its of fla##abilit$ are one of the #ost i#portant properties of a f el% These para#eters are a #eas re of the ran!e of the f el6air ratios over which an en!ine canoperate% H$dro!en has wide ran!e of fla##abilit$ in co#parison with other f els% One ofthe si!nificant advanta!es is that h$dro!en en!ine can r n on a lean #i+t re% hen en!ineis r n on sli!htl$ lean #i+t res f el econo#$ is !reater and the co#b stion reaction is#ore co#plete% Additionall$" the final co#b stion te#perat re can be lowered b$ sin!ltra*lean #i+t res" red cin! the a#o nt of NO + e#issions%

7%1%7 5ini# # I!nition Ener!$

The #ini# # ener!$ re/ ired for i!nition for h$dro!en is abo t an order of #a!nit deless than that re/ ired for !asoline% This enables h$dro!en en!ines to r n well on lean#i+t res and ens res pro#pt i!nition% Unfort natel$" since ver$ little ener!$ is necessar$to i!nite a h$dro!en co#b stion reaction" and al#ost an$ h$dro!en6air #i+t re can be

i!nited d e to wide li#its of fla##abilit$ of h$dro!en" hot !ases and hot spots on thec$linder can serve as so rces of i!nition" creatin! proble#s of pre#at re i!nition andflashbac&%

7%1%: J enchin! 4ap or Distance

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In the co#b stion cha#ber" the co#b stion fla#e is t$picall$ e+tin! ished at certaindistance fro# the c$linder wall d e to heat losses called as / enchin! distance% 'orh$dro!en" the / enchin! distance is less than that of !asoline" so that fla#e co#es closerto the wall before it is e+tin! ished% Th s it is #ore diffic lt to / ench a h$dro!en fla#ethan a !asoline fla#e%

7%1%= 2elf I!nition Te#perat re

The self i!nition te#perat re is the te#perat re that a co#b stible #i+t re # st reach before it will be i!nited witho t an e+ternal so rce of ener!$% 'or h$dro!en" the selfi!nition te#perat re is relativel$ hi!h% The hi!h self*i!nition te#perat re of h$dro!enallows lar!er co#pression ratios to be sed in h$dro!en en!ine witho t increasin! thefinal co#b stion te#perat re be$ond the self i!nition te#perat re and ca sin! pre#at re

i!nition% The h$dro!en is diffic lt to i!nite in a co#pression i!nition or dieselconfi! ration" beca se the te#perat res needed for this t$pe of i!nition relativel$ hi!h%

7%1% 'la#e 2peed

The fla#e speed of h$dro!en is nearl$ an order of #a!nit de hi!her than that of !asoline%'or stoichio#etric #i+t res" h$dro!en en!ines can #ore closel$ approach thether#od$na#icall$ ideal en!ine c$cle% At leaner #i+t res" the fla#e velocit$ decreasessi!nificantl$%

7%1%- Diff sivit$

H$dro!en diff sivit$" or its abilit$ to disperse in air" is considerabl$ !reater than that of!asoline%The hi!h diff sivit$ is advanta!eo s for two #ain reasons% 'irst" it facilitates thefor#ation of nifor# #i+t re of f el and air% 2econdl$" if a h$dro!en lea& does develop"the h$dro!en will disperse rapidl$% Th s nsafe conditions can either be avoided or#ini#i ed%

7%1%> Densit$

H$dro!en has e+tre#el$ low densit$% This creates two proble#s3 (1) a ver$ lar!e vol #e

is necessar$ to store eno !h h$dro!en to !ive a vehicle an ade/ ate drivin! ran!e" (7) theener!$ densit$ of h$dro!en air char!e and hence the power o tp t is red ced%

7%1% 'la#e characteristics

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H$dro!en fla#es are ver$ pale bl e and are al#ost invisible in da$li!ht d e to theabsence of soot% ;isibilit$ is enhanced b$ the presence of #oist re or i#p rities (s ch ass lf r) in the air% H$dro!en fla#es are readil$ visible in the dar& or s bd ed li!ht%

'i! re 73 Invisible H$dro!en 'la#e I!nitin! roo#

H$dro!en fla#es are al#ost invisible in da$li!ht%H$dro!en fires can onl$ e+ist in there!ion of a lea& where p re h$dro!en #i+es with air at s fficient concentrations% 'ort rb lent lea&s" air reaches the centerline of the lea&a!e et within abo t five dia#eters ofa lea&a!e hole" and the h$dro!en is dil ted to nearl$ the co#position of air withinro !hl$ .. to 1... dia#eters% This rapid dil tion i#plies that if the t rb lent lea& wereinto open air" the fla##abilit$ one wo ld e+ist relativel$ close to the lea&% Therefore"when the et is i!nited" the fla#e len!th is less than .. dia#eters fro# the hole (fore+a#ple" for a .%.:9 in61 ## dia#eter lea&" the fla#e len!th will be less than 19%> in6.%#)% In #an$ respects" h$dro!en fires are safer than !asoline fires% H$dro!en !as rises / ic&l$d e to its hi!h b o$anc$ and diff sivit$% Conse/ entl$ h$dro!en fires are vertical andhi!hl$ locali ed% hen a car h$dro!en c$linder r pt res and is i!nited" the fire b rnsawa$ fro# the car and the interior t$picall$ does not !et ver$ hot% 4asoline for#s a pool"spreads laterall$" and the vapors for# a lin!erin! clo d" so that !asoline fires are broadand en*co#pass a wide area%

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'i! re :3 H$dro!en 'la#e fro# R pt red ' el C$linder

7%7 enefits of H$dro!en Econo#$

idespread se of h$dro!en as an ener!$ so rce in this co ntr$ co ld help addressconcerns abo t ener!$ sec rit$" !lobal cli#ate chan!e" and air / alit$% ' el cells are ani#portant enablin! technolo!$ for the H$dro!en ' t re and have the potential to

revol tioni e the wa$ we power o r nation" offerin! cleaner" #ore*efficient alternativesto the co#b stion of !asoline and other fossil f els% These benefits are3* 2tren!then National Ener!$ 2ec rit$ Red ce 4reenho se 4as E#issions Red ce Air Poll tion I#prove Ener!$ Efficienc$

7%: H$dro!en 2tora!e and Deliver$

In en!ine applications the stora!e and portabilit$ of ade/ ate #ass of h$dro!en for

practical applications re#ain one of the #ost diffic lt proble#s $et to be overco#e%H$dro!en can be stored as a co#pressed !as in s itabl$ desi!ned hi!h*press re vessels%However" the ver$ low densit$ of h$dro!en in co#parison to other !aseo s f els" dictatesthat e+tre#el$ hi!h*press re c$linders that are s fficientl$ li!ht in wei!ht and co#pact invol #e need to be devised and sed% The co#pression of the !as to s ch hi!h press resre/ ires the e+pendit re of # ch e+pensive co#pression wor& and the provision of thenecessar$ infra str ct re% Also" these h$dro!en !as c$linders wo ld add si!nificantl$ tothe total wei!ht" cost and b l&iness of the f el installation%

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H$dro!en also can be carried on board vehicles and en!ine installations in the for# ofvario s #etallic h$drides that wo ld per#it the controlled release of h$dro!en thro !hthe s ppl$ of heat" often fro# the en!ine e+ha st !as or its coolin! water% These #ethodsare of li#ited sef lness as the$ add # ch cost and wei!ht while red cin! the fle+ibilit$of the f el s$ste# and contrib tin! to an increase in ndesirable e#issions% The carr$in!of h$dro!en as a cr$o!enic li/ id has its serio s li#itations also% The wor& andinfrastr ct re re/ ired to li/ ef$ h$dro!en are # ch too e+pensive and ener!$ intensiveto beco#e widel$ sable% The ener!$ cons #ed in the li/ efaction process can be p toaro nd :.F of the heatin! val e of the h$dro!en% Also" the cr$o!enic tan&s needed tocarr$ the li/ id h$dro!en" despite the ver$ s bstantial pro!ress #ade in recent $ears intheir desi!n" safet$ and #an fact re" re#ain relativel$ e+pensive and b l&$% 7%:%1 H$dro!en Deliver$ 5ethods

The h$dro!en c rrentl$ in the #ar&etplace for ind strial se is transported as a !as at low(1..*:.. psi!) or hi!h (:...* ... psi!) press re or as a cr$o!enic li/ id via !as

pipelines" !as or cr$o!enic li/ id tr c&s" t be trailers" bar!e" or rail cars% At hi!hvol #es" h$dro!en deliver$ b$ pipeline is c rrentl$ the lowest cost option% ,i/ efactionis often cost*effective in sit ations where lower vol #es are needed%

Co#pressed 4as and Cr$o!enic ,i/ id 2tora!eH$dro!en can be ph$sicall$ stored as either a !as or a li/ id% 2tora!e as a !as t$picall$re/ ires hi!h*press re tan&s ( ...*1."... psi tan& press re)% 2tora!e of h$dro!en as ali/ id re/ ires cr$o!enic te#perat res" since the boilin! point of h$dro!en at one

at#osphere press re is *7 7% . C% 5aterials*based H$dro!en 2tora!e

H$dro!en can also be stored on the s rfaces of solids (b$ adsorption) or within solids (b$absorption)% In adsorption" h$dro!en is attached to the s rface of a #aterial either ash$dro!en #olec les or as h$dro!en ato#s% In absorption" h$dro!en is dissociated into H*ato#s and then the h$dro!en ato#s are incorporated into the solid lattice fra#e wor&%H$dro!en stora!e in solids #a$ #a&e it possible to store lar!er / antities of h$dro!en ins#aller vol #es at low press re and at te#perat res close to roo# te#perat re% It is also

possible to achieve vol #etric stora!e densities !reater than li/ id h$dro!en beca se theh$dro!en #olec le is dissociated into ato#ic h$dro!en within the #etal h$dride latticestr ct re%

C rrent Technolo!$C rrent on*board h$dro!en stora!e approaches involve co#pressed h$dro!en !as tan&s"li/ id h$dro!en tan&s" #etal h$drides" carbon*based #aterials6hi!h s rface area sorbents"and che#ical h$dro!en stora!e% 2tora!e as a !as or li/ id or stora!e in #etal h$drides orhi!h s rface area sorbents constit te reversible on*board h$dro!en stora!e s$ste#s" since



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h$dro!en re!eneration or refill can ta&e place on*board the vehicle% 'or che#icalh$dro!en stora!e approaches (s ch as a che#ical reaction on board the vehicle to

prod ce h$dro!en)" h$dro!en re!eneration is not possible on*board the vehicle and th sthese spent #aterials # st be re#oved fro# the vehicle and re!enerated off board%

CHAPTER :

CO5 U2TION

:%1 Co#b stion Pheno#ena

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Co#b stion is a &e$ ele#ent of #an$ of #odern societ$Ks critical technolo!ies%Co#b stion acco nts for appro+i#atel$ percent of the worldKs ener!$ sa!e and isvital to o r c rrent wa$ of life% 2pacecraft and aircraft prop lsion" electric power

prod ction" ho#e heatin!" !ro nd transportation" and #aterials processin! all seco#b stion to convert che#ical ener!$ to ther#al ener!$ or prop lsive force%E+a#ples of co#b stion applications3

4as t rbines and et en!ines Roc&et prop lsion Piston en!ines 4 ns and e+plosives ' rnaces and boilers 'la#e s$nthesis of #aterials (f llerenes" nano*#aterials) Che#ical processin! (e%!% carbon blac& prod ction) 'or#in! of #aterials 'ire ha ards and safet$

Co#b stion is a co#ple+ interaction of ph$sical (fl id d$na#ics" heat and #ass transfer)"and che#ical processes (ther#od$na#ics" and che#ical &inetics)% Practical applicationsof the co#b stion pheno#ena also involve applied sciences s ch as aerod$na#ics" f eltechnolo!$" and #echanical en!ineerin!%The transport of ener!$" #ass" and #o#ent #are the ph$sical processes involved in co#b stion% The cond ction of ther#al ener!$" thediff sion of che#ical species" and the flow of !ases all follow fro# the release ofche#ical ener!$ in the e+other#ic reaction% The s b ect areas #ost relevant toco#b stion in the fields of ther#od$na#ics" transport pheno#ena" and che#ical &ineticscan be s ##ari ed as follows3

Ther#od$na#ics3 2toichio#etr$ Properties of !ases and !as #i+t res Heat of for#ation Heat of reaction E/ ilibri # Adiabatic fla#e te#perat re

Heat and 5ass Transfer3

Heat transfer b$ cond ction Heat transfer b$ convection Heat transfer b$ radiation 5ass transfer

'l id D$na#ics3 ,a#inar flows T rb lence



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Effects of inertia and viscosit$ Co#b stion aerod$na#ics

Che#ical inetics3

Application of ther#od$na#ics to a reactin! s$ste# !ives s the e/ ilibri #co#position of the co#b stion prod cts and #a+i# # te#perat re correspondin! to thisco#position" i%e% the adiabatic fla#e te#perat re% However" ther#od$na#ics alone is notcapable of tellin! s whether a reactive s$ste# will reach e/ ilibri #% If the ti#e scalesof che#ical reactions involved in a co#b stion process are co#parable to the ti#e scalesof ph$sical processes (e%!% diff sion" fl id flow) ta&in! place si# ltaneo sl$< the s$ste##a$ never reach e/ ilibri #% Then" we need the rate of che#ical reactions involved inco#b stion% Co#b stion processes can be s b*divided based on #i+in! as pre#i+ed"non* pre#i+ed and partiall$ pre#i+ed% Co#b stion in ho#o!eneo s*char!e spar&*i!nition en!ines and lean b rn t rbines is nder pre#i+ed conditions% Contrastin!l$"co#b stion in Diesel en!ines or ind strial f rnaces is nder non*pre#i+ed conditions% In

the nonpre#i+ed cases" f el is in ected into the co#b stion cha#ber alon! with air"where it is i!nited d e to pre*e+istin! hot !ases or a to*i!nites d e to hi!h te#perat ressecond criterion for s bdividin! the t rb lent co#b stion relates to the ratio oft rb lence to che#ical reaction ti#e scales% Above a certain cross*over te#perat re"h$drocarbon o+idation occ rs b$ chain*branchin!% Chain*branchin! ceases when thete#perat re falls below this li#it" th s ca sin! e+tinction of fla#e% This crossoverte#perat re increases with press re% hile the fast che#ical processes can be si# latedsin! e/ ilibri # approach" slow che#ical reactions re/ ire bein! #odeled sin! &inetice+pressions% Presence of slow and ver$ fast reactions in the sa#e reaction #echanis# can

pose proble#s in n #erical sol tions d e to stiffness of the e/ ations% 5ost ind strialco#b stion processes involve t rb lent flows% ,a#inar flows are enco ntered in few

ind strial cases and a lar!e n #ber of acade#ic cases% 'low si# lations re/ ire thesol tions of balance e/ ations (of #ass" ener!$ and #o#ent #)% These e/ ations are#ostl$ of partial differential for#% ,a#inar flow cases are # ch si#pler andstrai!htforward and can often be appro+i#ated with one di#ensional treat#ent% Presenceof t rb lence in the flow re/ ires special treat#ent to acco nt for the co#ple+ nat re oft rb lence% Co#b stion re/ ires that f el and o+idi er be #i+ed at the #olec lar leveland in t rb lent flows< this #i+in! is done not onl$ b$ #olec lar (ther#al) processes" b talso b$ the t rb lent fl ct ations% 5olec lar #i+in! ta&es place at the interface of thes#allest eddies%

:%7 H$dro!en Co#b stion

One the reasons for which we are interested in h$dro!en is beca se its che#istr$ isconsidered a startin! point for the #ore co#ple+ h$drocarbon che#istr$% It is i#portantto stress that in the a to i!nition sta!es of an$ fla#e" the f el air #i+t re #a$ follow alow te#perat re reaction #echanis# and in the latter sta!es" an e+plosive reaction d e tothe increase in te#perat re and6or press re ca sin! the operatin! point to shift between



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the re!ions of the !raph of fi! re =% This point is especiall$ si!nificant in h$drocarbonche#istr$" beca se it is in the low*te#perat re re!i#e that partic lar poll tantco#po nds are for#ed% 'i! re = depicts the e+plosion li#its of a stoichio#etric #i+t re"

b t e/ ivalent plots can be obtained for #an$ different #i+t re co#positions%

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'i! re =3 E+plosion ,i#its of 2toichio#etric H$dro!en*O+$!en 5i+t re

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The !eneral characteristics are3 The first and second li#its are ones that correspond to conditions of ver$ low

press res ( p to an absol te press re of abo t .%: bar) and will not be considered%O r lowest wor&in! press re is at#ospheric press re" 1 bar%

The third li#it follows the trend that one wo ld e+pect fro# si#ple densit$considerations% As the press re increases" the initial densities of the reactantsincrease and a lower te#perat re is necessar$ for the reactions to beco#e fasteno !h for e+plosion% ' rther#ore" notin! the lo!arith#ic a+is" we can see thatthe effect of te#perat re is # ch stron!er than that of press re" a trend one wo ld

e+pect and correctl$ capt red b$ the considerations of si#plified one*stepArrheni s che#istr$%



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CHAPTER =

4RID 4ENERATION AND 5ATHE5ATICA, 5ODE,IN4

=%1 5odel !eo#etr$ and #esh

The !eo#etr$ of the c$lindrical cha#ber sed in this st d$ is shown in fi! re %The non pre#i+ed h$dro!en and air are in ected into the c$lindrical cha#ber fro# inlets located atone a+ial end as shown in fi! re % A s#all no le in the center of the co#b stor

introd ces h$dro!en at 9.#6s and air enters the co#b stor coa+iall$% eca se of the a+ials$##etr$ of the co#b stion cha#ber" the !eo#etr$ is #odeled as a two*di#ensionala+i*s$##etric #odel%

'i! re 3 2che#atic Dia!ra# of the Co#b stion Cha#ber for H$dro!en Co#b stion5odelin!

=%1%1 4rid 4eneration

5esh or !rid !eneration consists of creatin! a set of !rid points alon! the bo ndaries andthro !ho t the do#ain of interest% The n #erical si# lation of Navier*2to&es e/ ationre/ ires the !en*eration of !rids in the flow do#ain% As the h$dro!en in ected centrall$and air enters co*a+iall$ in the co#b stion cha#ber #ore variation in the properties will

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be seen alon! the central a+is as well as at the inlet% 2o cl sterin! is done fro#co#b stion wall s rface towards central a+is and fro# inlet towards e+it%

'or the scenarios anal$ ed in this st d$" the n #ber of nodes and n #ber of / adrilateralcells are 1>. and 1-1 respectivel$ sed to #esh the #odel for the C'D si# lations%This fine #esh si e will be able to provide !ood spatial resol tion for the distrib tion of#ost variables within the co#b stion cha#ber%

'i! re -3 Co#b stion Cha#ber 4rid

=%7 5athe#atical 5odelin!

5odelin! is the representation of a ph$sical s$ste# b$ a set of #athe#atical relationshipsthat allow the response of the s$ste# to vario s alternative inp ts to be predicted% InCo#p tational 'l id D$na#ics" we #odel the ph$sical s$ste# involvin! fl id flowwithin the definite bo ndaries b$ the set of #athe#atical e/ ations s all$ in differentialfor# and obtain the n #erical sol tion of these !overnin! e/ ations describin! the fl id

flow b$ the se of co#p tational #ethods% The !overnin! e/ ations #a$ incl de3 the setof the Navier*2to&es e/ ations" contin it$ e/ ation" and an$ additional conservatione/ ations" s ch as ener!$ or species concentrations% The fl id flow is #odeled b$ the!overnin! e/ ations" which show the effect of the !overnin! pheno#ena on the fl idflow% These !overnin! pheno#ena #a$ incl de3 cond ction" convection" diff sion"t rb lence" radiation and co#b stion% The followin! is brief description of the !overnin!e/ ations%

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=%: 4overnin! E/ ations=%:%1 Contin it$ E/ ationConsiderin! the law of conservation of #ass the contin it$ e/ ation"

G %div ( ) G %div ( ) @ .

In the !iven e/ ation the first ter# is the rate of chan!e of densit$% In the second and thethird ter#s the diver!ence div is the fl + densit$ or fl +6vol #e% The first two ter#sshow the two wa$s the densit$ of the fl id ele#ent chan!es% If we ass #e the

inco#pressibilit$ condition i%e% densit$ of the fl id is constant" the above e/ ationred ces to" div ( ) @.%

=%:%7 5o#ent # E/ ationsAlso &nown as Navier and 2to&es e/ ations" these are derived for a visco s flow and !ivethe relationships between the nor#al6shear stresses and the rate of defor#ation (velocit$field variation)% e can obtain these e/ ations b$ #a&in! a si#ple ass #ption that thestresses are linearl$ related to the rate of defor#ation (Newtonian fl id)" the constant of

proportionalit$ for the relation bein! the d$na#ic viscosit$ of the fl id% 'ollowin! isstated the Navier and 2to&es e/ ation for i*th coordinate direction"

G @ * G G 'i

here is the visco s force tensor and ' represents a bod$ force in the *th coordinate

direction% In practical sit ations of co#b stion" all fl ids are ass #ed to be Newtonianand the visco s stress tensor is3

@ L M G * L M

here L is the #olec lar viscosit$ which depends on the fl id% The ronec&er delta is

@1"if i @ " . otherwise%

=%:%: 2pecies



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G @ * G ( @1" 7" : n)

here n is the n #ber of species" is the #olec lar diff sivit$ fl + of the species inthe *th coordinate direction" is the #ass reaction rate of this species per nit vol #e"

and is the #ass fraction of species %

The diff sive fl +" "can be appro+i#ated b$3

@ * @ *

where is the 2ch#idt n #ber of the species " defined as3

@

here D is the #olec lar diff sivit$ of the species relative to the other species%

=%:%= 2tandard &*Q t rb lence #odelIn this si#ple #odel" two additional transport e/ ation are solved for the two t rb lence/ antities vi % the t rb lent &inetic ener!$ & and the ener!$ dissipation rate Q% These two/ antities are related to the pri#ar$ variables and can !ive a len!th scale and ti#e scaleto for# a / antit$ with di#ension of " th s #a&in! the #odel co#plete (no #ore

flow*dependent specifications are re/ ired)% This is a widel$ sed #odel in C'Dsi# lations%

@

The balance e/ ation for & is3

G ) @ *(76:) G 3 G M * G

=%= o ndar$ conditions



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The inlet te#perat re of h$dro!en and air is considered to be nifor# at :.. % A fi+ed"nifor# velocit$ 9. #6s is specified at the h$dro!en inlet%A+is*s$##etric bo ndar$conditions are applied alon! the central a+is of the co#b stion cha#ber% At the e+it" a

press re o tlet bo ndar$ condition is specified with a fi+ed press re of 1%.1:7 S 1. Pa%At the cha#ber wall" no*slip bo ndar$ condition and no species fl + nor#al to the walls rface are applied% The ther#al bo ndar$ condition on the cha#ber wall is ta&en asadiabatic wall condition%

CHAPTER

C'D 2I5U,ATION

A n #ber of n #erical si# lations have been perfor#ed to st d$ the co#b stion

pheno#ena nder adiabatic wall conditions when h$dro!en air #i+t re chan!es fro#lean to rich and also at different #ass flow rate of #i+t re% 'i! re% > shows the conto rsof te#perat re ( ) on the cross section alon! central a+is of co#b stion cha#ber atstoichio#etric air f el ratio i%e% at @1% And 'i! re shows the !as te#perat redistrib tion alon! the central a+is% It can be seen fro# 'i! res > and that the hi!hestte#perat re is obtained at the e+it of co#b stion cha#ber% The fla#e te#perat re can beas hi!h as 7:- which is al#ost the sa#e as the adiabatic fla#e te#perat re of theCo#b stion of non pre#i+ed stoichio#etric h$dro!en*air #i+t re% 'i! res 9 to show theconto rs of #olec lar species on the cross*section alon! the central a+is at @1 nderadiabatic wall condition%

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'i! re 3 Conto rs of 5ole fraction of

'i! re 93 Conto rs of 5ole fraction of N 7



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'i! re 1.3 Conto rs of 5ole fraction of O 7

'i! re 113 Conto rs of 5ole fraction of H 7

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CHAPTER -

CONC,U2ION

In this wor&" the C'D based co#b stion si# lations have been applied to anal$ e theco#b stion characteristics of non*pre#i+ed h$dro!en*air in a 7D co#b stor% The C'Dsi# lations" ta&in! in to acco nt the co plin! of fl id d$na#ics" heat transfer anddetailed che#ical &inetics" are sed to investi!ate the effects of vario s operatin!conditions% The co#b stor perfor#ance is eval ated b$ predictin! the te#perat res ofe+it !as of the co#b stor and o ter wall of the co#b stor% To #a&e the co#b storoperable" the heat o tp t sho ld #eet the desi!n criteria" the wall te#perat re sho ld belower than the #aterial allowable te#perat re and the e+it !as te#perat re sho ld behi!h eno !h%



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CHAPTER >

RE'ERENCE21% Das ,%5%" H$dro!en*o+$!en reaction #echanis# and its i#plication to h$dro!enen!ine co#b stion" 713>.:*>1 International Bo rnal of H$dro!en Ener!$" 199-%7% Bin!son! H a" 5en! " richi #ar" N #erical si# lation of the co#b stion ofh$dro!enair #i+t re in #icro*scaled cha#bers% Part II3 C'D anal$sis for a #icro*co#b stor -.3: .>*: 1 " che#ical en!ineerin! science" 7.. %:% D 2paldin! (19 >) VAnalo! e for hi!h*intensit$ stead$*flow co#b stion

pheno#enaV" Proc% I 5ech E ,ondon" vol 1>1" no 1." pp: :*=11%=% H Chesters" R2 Howes" I5D Hallida$ 0 AR Philip (19=9)" B Iron 0 2teel Inst vol 1-7"no =" pp : " :97" =.1%% Bones" % P%" and ,a nder" % E% B% Heat 5ass Transfer" 1 3:.1 (19>7)%-% ,a nder" % E%" and 2paldin!" D% % Co#p% 5ethods Appl% 5ech% En!in% :37-9 (19>=)%>% in! RO" Rand 5% The h$dro!en en!ine% Canad B Technol 19 < ::3== -9%% 4ha i A% ari# H$dro!en as a spar& i!nition en!ine f el" 7 3 -9 >>InternationalBo rnalof H$dro!en Ener!$" 7..:%9% N%5%5arinov" C% % estbroo& and %B%Pit Detailed And 4lobal Che#ical inetics5odel 'or H$dro!en U%2 Depart#ent Of Ener!$" ,awrence ,iver#ore National,aborator$%1.% No#an ,%Bohnson and Anthon$ A% A#sden N #erical 5odelin! Of H$dro!en*' eled Internal Co#b stion En!ines%11% Binson! H a" 5en! " richi" N #erical si# lation of the co#b stion ofh$dro!en air #i+t re in #icro*scaled cha#bers% Part I3 ' nda#ental st d$ -.3:=9>*: .-"che#ical en!ineerin! science" 7.. %17% arlow" R% 2%" and Carter" C% D%" Co#b st% 'la#e 9>37-1 (199=)%1:% l r$" 5%" and 2chlatter" 5% (199>)% Technical report"http366www%ltnt%eth %ch6co#b stion6no+" ETH W rich%1=% A% Obie!lo" B% 4ass" D% Po li&a&os" Co#parative 2t d$ of 5odelin! a H$dro!en

Nonpre#i+ed T rb lent 'la#e" 17731>-19=" Co#b stion And 'la#e" 7...%1 % 4lass#an" I%" 199-%Co#b stion% Acade#ic Press" California%1-% 2% ;erhelst" R% 2ierens" H$dro!en en!ine*specific properties" International Bo rnal ofH$dro!en Ener!$ 7- (7..1) 9 >99.%

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2 N $ 4 & l # C ll ! Of E !i i ! D # Of 5 h i l E !i i !

51-Varghese K George-CFD Simulation of Hydrogen Combustion-4

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