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Peak gas temperature is about 2500 K
Heat flux from gases to combustion chamber walls can reach10 MWm2
!ombustion chamber surface temperatures must be less than
"00#! for cast iron an$ %00#! for aluminum allo&s to pre'entfatigue cracking
(as)si$e surface of the c&lin$er wall must be kept below1*0#! to pre'ent $eterioration of the lubricating oil film
+park plugs an$ 'al'es must be kept cool to a'oi$ knock an$preignition
,n general- heat transfer affects engine performance- efficienc&an$ emission
Importance of engine heat transferImportance of engine heat transfer
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Heat transfer and engine energy balanceHeat transfer and engine energy balance
( )f f a a b cool misc f a em h m h P Q Q m m h+ = + + + +& && & & &
, ,b cool misc e ic e s f LHV P Q Q H mh m Q+ + + + =& & & & &
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Heat transfer and engine energy balanceHeat transfer and engine energy balance
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Modes of heat transferModes of heat transfer
Conduction
Convection
Radiation
. k T= &
( )c wq h T T = &
( )" "1 2q T T= &
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(as si$e
Wall
!oolant si$e
( ) ( )" ", , ,CV R c g g w g g w g q q q h T T T T = + = + & & &
( ), ,w g w cCN
w
k T Tq q
t
= =& &
( ), ,CV c c w c cq q h T T = = & &
Overall heat transfer processOverall heat transfer process
Heat flow across cylinder wall
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Convective heat transferConvective heat transfer
Diensional analysisDiensional analysis
!unctional for of relationships which govern the gas"side heat transfer
coefficient is of the for
!orulas for calculation heat transfer coefficient are based on relationship
1 1 0, , , , , , , , ..., , , , ...,p pc ch
c m n
p
S B ch B qBF r R ! !k k L c NT
=
&
Nu Re Prm na=
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Heat transfer correlationsHeat transfer correlations
Heat transfer correlations fall into three t&pes inten$e$ topre$ict
/ time)a'erage$ heat flux to combustion chamber walls
/ instantaneous spatiall& a'erage$ heat flux to walls
/ instantaneous local heat fluxes
Main parameters use$ are
/ 'elocit& to calculate e&nol$s number
/ gas temperature at which gas properties are calculate$
/ gas temperature use$ in con'ecti'e heat transfer e.uation
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Correlations for tie"averaged heat flu#Correlations for tie"averaged heat flu#
Taylor and Toong$ Data fro %& different engines
'ssuptions( coolant and wall teperatures vary little between designs and
effects of geoetry is sall
Thus) at a given fuel*air ratio) convective part of heat flu# correlate with Re
'verage effective gas teperature +governing teperature,
-usselt
Reynolds
( ) 0,c g a"h T T # =
( )( ) ( )2"
" ,,
Nu
g g a cg a c g
QB Q
Bk T TB T T k = =
& &
( )2
"
"
Re
g
mB m
BB
= =
& &
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Correlations for instantaneous spatialCorrelations for instantaneous spatial
averaged coefficientsaveraged coefficients
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Correlations for instantaneous spatialCorrelations for instantaneous spatial
averaged coefficientsaveraged coefficients
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Correlations for instantaneous spatialCorrelations for instantaneous spatial
averaged coefficientsaveraged coefficients
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Correlations for instantaneous spatialCorrelations for instantaneous spatial
averaged coefficientsaveraged coefficients
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Correlations for instantaneous localCorrelations for instantaneous local
coefficientscoefficients
.e!euvre) Dent and /ulaian$ 'pplied to DI diesel with swirl$
correlation forula
heat flu# at radius r
'lternative approach is to use 0onal odeling$ 1onal odels are ore accurate
than global ones
0 %%%0 *
0 0%
..
. pc
ch l $l
k k
=
( ) ( ) ( )
0 *2
0 02%
.
. g wk r
q r T r T r r
=
&
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Radiative heat transferRadiative heat transfer
wo sources of ra$iati'e heat transfer are/ high)temperature burne$ gases
/ soot particles in the $iesel engine flame
a$iation from soot particles in the $iesel engine flame is
about fi'e times the ra$iation from gaseous combustionpro$ucts
a$iati'e heat transfer in con'entional +, engines can beneglecte$
,n $iesel engines ra$iati'e heat transfer is 20 to %5 percent ofthe total heat transfer
a$iati'e heat transfer term is usuall& incorporate$ intocorrelations for con'ecti'e heat transfer
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Theral loading and coponent teperaturesTheral loading and coponent teperatures
Heat flux to combustion chamber walls 'aries with engine$esign an$ operating con$itions
Heat flux to 'arious parts of combustion chamber is not thesame
3onuniform heat flux an$ the $ifferent thermal resistancesbetween locations on the combustion chamber surface an$cooling flui$ result in nonuniform temperature $istribution
within engine components
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Coponent teperature distributionCoponent teperature distribution
3ormall& heat flux is the highest
/ in the center of the c&lin$er hea$
/ in the exhaust 'al'e seat region
/ to the center of the piston
Heat flux is lowest to the c&lin$er walls
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Piston teperature distributionPiston teperature distribution
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Cylinder head teperature distributionCylinder head teperature distribution
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Cylinder liner teperature and heat flu#Cylinder liner teperature and heat flu#
distributiondistribution
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2#haust valve teperature distribution2#haust valve teperature distribution
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+pee$- loa$- e.ui'alence ratio- compression ratio- spark orin4ection timing- charge motion- mixture inlet temperature-coolant temperature an$ composition- wall material- wall$eposits effect the magnitu$e of heat flux an$ temperature
$istribution in the engine components Woshni correlation an$ relation for heat transfer flux ma& be
use$ for pre$icting tren$s
2ffect of engine variables2ffect of engine variables
( ) ( ) ( ) ( ) ( )0 2 0 * 0 55 0 *2
W m K % 2 m kPa K m s. . . .
.ch B p T w
=
( )c wq h T T = &
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2ffect of engine variables +/I engines,2ffect of engine variables +/I engines,
/peed and load/peed and load
Relative iportance of heat lossesper cycle decreases as speed 3load increase) but average heattransfer per unit tie increases
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2ffect of engine variables +/I engines,2ffect of engine variables +/I engines,
24uivalence ratio24uivalence ratio
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2ffect of engine variables +/I engines,2ffect of engine variables +/I engines,
Copression ratioCopression ratio
,ncreasing compression ratio $ecreases total heat flux to the
coolant until rc%10- thereafter heat flux increases slightl& as rc
increases
ffect of changes in compression ratio on component
temperature $epen$s on location6 (enerall&- with increasing
compression ratio7
/ hea$ an$ exhaust 'al'e temperature $ecrease $ue to lower expansion
an$ exhaust stroke temperatures
/ piston an$ spark plug electro$e temperatures increase 8at constantthrottle settings9 $ue to higher peak combustion temperatures
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2ffect of engine variables +/I engines,2ffect of engine variables +/I engines,
/par5 tiing/par5 tiing
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2ffect of engine variables +/I engines,2ffect of engine variables +/I engines,
/wirl and s4uish/wirl and s4uish
,ncrease$ gas 'elocities- $ue to swirl of s.uish motion- result in
higher heat fluxes
( ) ( ) ( ) ( ) ( )0 2 0 * 0 55 0 *2
W m K % 2 m kPa K m s. . . .
.ch B p T w
=
( )c wq h T T = &
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2ffect of engine variables +/I engines,2ffect of engine variables +/I engines,
Inlet teperatureInlet teperature
Heat flux increases linearl& with increasing inlet temperature
,ncrease of 100 K gi'es 1% percent increase in heat flux
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2ffect of engine variables( coolant teperature2ffect of engine variables( coolant teperature
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Heat transfer calculationHeat transfer calculation
:or con$uction an$ con'ection heat flowrate through material la&er
( )h cQ h" T T = &
Heat transfer rate is e.ual for all la&ers
where
otal thermal resistance
( ) ( ) ( ) ( )tot hg c g hg wh w wh wc c wcQ h a T T h " T T h " T T h " T T = = = = &
( ) ( ) ( )hg c tot hg wh g wh wc w wc c cQ T T R T T R T T R T T R= = = = &
1 for con'ection for con$uctionR h" R L k"= =
tot g w c
R R R R= + +
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Heat transfer calculationHeat transfer calculation
:or c&lin$er gas)wall boun$ar& la&er fro
an& instant
!&cle a'erage$ 'alues
+implest le'el is to assume a'erage thickness an$ con$ucti'it& for the c&lin$er
;wall< an$ coolant boun$ar& la&er6 hen
( )g g wQ h " T T = &
g g g w gQ Q C&C'(R h h C&C'(R T T Q h "= = = + & & &
( ) ( ) ( ) ( ) ( )1g g w w w c w w w cQ h " T T R T T k " L T T = = = &
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Heat transfer networ5Heat transfer networ5
:or isolate$ c&lin$er hea$
( )wH cH g g wHT TQ h " T T H
= = &
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Heat transfer networ5Heat transfer networ5
:or connecte$ liner an$ piston heat balances- at point TwL
at point TN)'*
at point TwP
gL wLwL c N)'* wL
o!t f
T TT T T T Q Q
F " '
= = + +& &
gP N)'*N)'* wL N)'* oil T TT T T T
' + * B
+ =
+
gP wPN)'* wP T TT T
* B
=
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Heat transfer networ5Heat transfer networ5
hermal resistances7
1 2
1 1
L L
Fh " h "
= + ( )1 g PB h "= ( )1 g L" h "=
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Ratio of coolant heat flow rate to
bra5e power as a function of
engine speed$
=ifferent si>e an$ t&pes of engines7
8a9 small automoti'e $iesels?
8b9 larger automoti'e $iesels?
8c9 'arious $iesels
8$9 k i iti i
Heat transfer and engine energy balanceHeat transfer and engine energy balance