3 thermochemistry of fuel-air mixtures
TRANSCRIPT
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33TOPICTOPIC
Thermochemistry ofThermochemistry offuel-air mixturesfuel-air mixtures
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Whats covered in this sectionWhats covered in this section
Characterization of flames
Fuels
Stoichiometry
First law and combustion
Second law applied to an engine
Chemical equilibrium
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Characterization of flamesCharacterization of flames
Combustion of the fuel-air mixture controls engine power, efficiency and
emissions.
Combustion phenomena are different for spark-ignition engines and diesels
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Combustion phenomenaCombustion phenomena
n spark-ignition engines!
fuel is mixed with air in the intake system
spark initiates the combustion
flame de"elops from the #kernel$ created by spark discharge and
propagates across the cylinder to combustion chamber walls
at the walls, the flame is #quenched$ or extinguished
%ndesirable combustion phenomenon & 'knock(
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Combustion phenomenaCombustion phenomena
n diesels!
fuel is in)ected into the cylinder near the end of compression process
fuel is self ignited by hot air
burning then proceeds as fuel and air mix
Fuel-air mixing plays a controlling role in the diesel combustion process
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Key combustion phenomenaKey combustion phenomena
Combustion process is a fast exothermic gas-phase reaction.
Flame is a combustion reaction which can propagate subsonically through the
space
*eaction zone is usually called theflame front.
+he generation of heat and acti"e species accelerate the chemical reaction the
supply of fresh reactants, go"erned by the con"ection "elocity, limits the
reaction. hen these processes are in balance, a steady-state flame results
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Flames classificationFlames classification
Composition of reactants as they enter the reaction zone!
premixed flame, diffusion flame
as flow regime!
laminar flame, turbulent flame
Change in flame structure and motion with time!
steady flame, unsteady flame
nitial phase of reactants!
gas, liquid, solid
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Characterization of flamesCharacterization of flames
+he con"entional spark-ignition flame is a premixed unsteady turbulent
flame, and the fuel-air mixture through which the flame propagates is in the
gaseous state
+he diesel engine combustion process is unsteady turbulent diffusion flame,
and the fuel is initially in the liquid phase
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Ideal gas modelIdeal gas model
as species that make up the working fluid in C /ngines can be treated as ideal
gas, for which
pV mRT nRT= =
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FuelsFuels
0ctually blends of many different hydrocarbons
1redominantly hydrogen 23456 by mass7 8 carbon 239:6 by mass7
;iesel fuel can contain some sulfur 23467
0lcohol fuels contain some oxygen
replaced by 4 ?>
/thanol = ethane with 4 > replaced by 4 ?>
0ppendix ;, page @4A in >eywood contains data on many different fuels
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Fuel types Alkyl compoundsFuel types Alkyl compounds
Single bonded open-chain saturated hydrocarbon
molecules
atom 2radical7 makes it methyl, ethyl,
propyl etc.
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Fuel types Alkyl compoundsFuel types Alkyl compounds
Single bond ring hydrocarbons
%nsaturated ring can be broken andadditional hydrogen added
Cyclopropane, cyclobutane,
cyclopentane, etc.
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Fuel types Alkyl compoundsFuel types Alkyl compounds
?pen-chain hydrocarbons containing double
bond
%nsaturated
/thylene, propylene, butylene, etc.
Same formula as cycloparaffins, butdifferent structure
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Fuel types Alkyl compoundsFuel types Alkyl compounds
?pen-chain hydrocarbons containing one
carbon-carbon triple bond
%nsaturated
0cetylene, etc.
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Fuel types AromaticsFuel types Aromatics
enzene 2C:>:7 is the building block
Dery stable hydrocarbon
+oluene 2CE>97, xylene 2C9>47, etc.
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Fuel types AlcoholsFuel types Alcohols
?ne > is replaced by hydroxyl radical
57 methanol 2C>G?>7, /thane2CH>:7 ethanol 2CH>A?>7 etc.
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Fuel compositionFuel composition
ra"imetric composition is gi"en by mass fractions of C and > in the fuel.
%sed for liquid fuels
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Combustion stoichiometryCombustion stoichiometry
oing from reactants 2fuel I air7 to products
;epends only on conser"ation of mass for each atom
;one on a #per kmole of fuel$ basis
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ropane combustion !ith the "ustropane combustion !ith the "ust
right amount of o#ygenright amount of o#ygen
G 9
G 9 H H H
G 9 H H H
1ropane C >
C > ? C? > ?
Carbon balance! G 4
>ydrogen balance! 9 H 5
H G 5?xygen balance! H H A
H
C > A? GC? 5> ?
a b c
b
c c
a b c a
=
+ +
=
= =
+= + = =
+ +
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Complete combustionComplete combustion
/nough oxygen to completely oxidize 2burn7 the fuel
0ll carbon oxidizes to C?H, all hydrogen to >H?
?His used to form >H? first, then the rest is used to form C?
0ny lefto"er ?Hthen con"erts C? into C?H
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Composition of airComposition of air
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$eneral stoichiometry$eneral stoichiometry
0pproximate a fuel with acarbon atoms and bhydrogen atoms
( )
( ) ( )
H H H H HC > ? G EEGJ C? > ? G EEG J5 H 5
5 G4 @@9 G EEG H9 4:
4H 44 4 9
. .
. . .
. .
a b
s
b b ba a a
a bAF
a b
+ + + + + +
+ + =
+
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%#ample &%#ample &
?ctane 2C9>497 is burned with the stoichiometric amount of air.
CalculatetheAFand the molecular weights of the reactants and the products, as
well as the dew-point temperature of the products.
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%#ample &%#ample &
?ctane 2C9>497 is burned with the stoichiometric amount of air.
CalculatetheAFand the molecular weights of the reactants and the products, as
well as the dew-point temperature of the products.
( )
( )
( )
H H H H H
9 49 H H H H H
9 49
C > ? G EEGJ C? > ? G EEG J5 H 5
C > 4H A ? G EEGJ 9C? @> ? G EEG 4H AJ
4H A G4 @@9 G EEG H9 4: kg of air4A 4H
4H F44 9 4 FF9 49 kg of fuel
a b
s
a b
b b ba a a
AF
= =
+ + + + + +
+ + + +
+ = =
+
. .
. . . .
. . . .
.
. .
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%#ample 'eactants%#ample 'eactants
( )
( ) ( )
9 49
H
H
C >
?
J
4 4H A 4 G EEG : E kmole
4 : E 4E
4H A : E H:
5E H : E EEE
4E 445 H: G4 @@9 EEE H9 4:
kgH@ 4
kmol
r
r i i
r
r
n
y
y
y
M y M
M
= + + =
= =
= =
= =
= = + +
=
. . .
. .
. . .
. . .
. . . . .
.
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%#ample roducts%#ample roducts
( ) ( ) ( )
H
H
H
C?
> ?
J
9 @ 5E H :5 H kmole
9 :5 H 4HA
@ :5 H 45
5E H :5 H EGA
4HA 55 44 45 49 4: EGA H9 4:
kgH9 E
kmole
pr
pr i i
pr
pr
n
y
y
y
M y M
M
= + + =
= =
= =
= =
= = + +
=
. .
. .
. .
. . .
. . . . . .
.
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%#ample de!point temperature%#ample de!point temperature
( )
H
H
> ?
> ?
o
45
45 44 GG 45 4@ k1a
AH E C
.
. . .
.
v
dp sat v
y
p y p
T T p
=
= = =
= =
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%#cess air%#cess air
( )
( )
( ) ( )
H H H H H H
H H H H H H
C > ? G EEGJ C? > ? ? G EEG JH
5
H H H H H 4
H 5
C > ? G EEGJ C? > ? -4 ? G EEG JH
a b s s
s
s s s
a b s s s
ba x
ba
b bx a a
ba
+ + + + +
= +
= = + =
+ + + + +
. .
. .
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%(uivalence ratio ) relative ratio%(uivalence ratio ) relative ratio
( ) ( )
( )
( )
H H H H H HC > ? G EEGJ C? > ? -4 ? G EEG JH
GH G EEG H9 4:
4H 4 4 9
GH G EEG H9 4:
4H 4 4 9
4
/qui"alenceratio
*elati"e ratio
a b s s s
s
a
s
s
s a
a s
ba
AFa b
AFa b
AF FA
AF FA
+ + + + +
+
= +
+ =
+
= = =
. .
. .
. .
. .
. .
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*ean+ and rich+burn mi#tures*ean+ and rich+burn mi#tures
Fuel - lean 4 4
Stoichiometric 4 4
Fuel-rich 4 4
< >
= =
> 497 is burned with HA6 excess air. CalculatetheAFand the molecular
weights of the reactants and the products, as well as the dewpoint temperature of
the products.
( ) ( )
( )
( )
H H H H H H
9 49 H H H H H H
9 49 4 HA
C > ? G EEGJ C? > ? -4 ? G EEG JH
C > 4A :HA ? G EEGJ 9C? @> ? G 4HA? A@J
4A :HA G4 @@9 G EEG H9 4: kg air49 @
4H 4 9 4 9 49 kg fuel
a b s s s
a s
a b
ba
AF AF
= = =
+ + + + +
+ + + + +
+ = = =
+
.
. .
. . .
. . . ..
. .
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'eactants'eactants
( )
( ) ( )
9 49
H
H
C >
?
J
4 4A :HA 4 G EEG EA : kmole
4 EA : 4G
4A :HA EA : HE
A@ EA : E9
4G G5 HGH HE G4 @@9 E9 H9 4:
kg kgH@ H@ 4
kmole kmol
r
r i i
r
r
n
y
y
y
M y M
M
= + + =
= =
= =
= =
= = + +
=
. . .
. .
. . .
. .
. . . . . .
. .
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roductsroducts
( ) ( )
( ) ( )
H
H
H
H
C?
> ?
?
J
9 @ G 4HA A@ E@ 4 kmole
9 E@ 4 44
@ E@ 4 445G 4HA E@ 4 5
A@ E@ 4 E5A
44 55 44 445 49 4:
5 G4 @@9 E5A H9 4:
kg kgH9 9 H9 E
kmole kmol
pr
pr i i
pr
pr
n
y
yy
y
M y M
M
= + + + + =
= =
= == =
= =
= = +
+ +
=
. .
. .
. .. . .
. .
. . . .
. . . .
. .e
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/e!point temperature/e!point temperature
( ) ( )
H
H
> ?
> ?
o o
445
445 44 GG 44 AA k1a
59 C AH E C
v
dp sat v
y
p y p
T T p
=
= = =
= =
.
. . .
.
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%#ample dry gas analysis%#ample dry gas analysis
+he measured dry exhaust gas composition of a propane-fueled S engine is gi"en
below 2water was remo"ed before the measurement7. Calculate the equi"alence
ratio.
C?H= 4.96, ?H= 5.A6, C? = 6, >H= 6
Solution
( )G 9 H H H H H HG.:C > HH A ? G EEGJ 4 9C? 45 5> ? 5 A? 95 @J
4 HA
9
+ + + + +
=
=
. . . . . .
.
.
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%nergy and enthalpy balances%nergy and enthalpy balances
First law and combustionFirst law and combustion
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Combustion at constant 01 constant 2Combustion at constant 01 constant 2
Combustion at
constant V,
constant T
R P R P P RQ W U U = ( ) ,R P P R V TQ U U U = =
( ),V T
U
& heat of reaction at constant "olume at temperature T
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Combustion at constant p1 constant 2Combustion at constant p1 constant 2
( )P
R P P RR
W pdV p V V = =
( )R P P R P RQ p V V U U =
( ) ( ) ,R P P P R R P R p TQ U pV U pV H H H = + = =
( ) ,p TH & heat of reaction at constant pressure at temperature T
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%nergy of reactants and products%nergy of reactants and products
U(or H) of reactants
and products as a
function of temperature
( ) ( ) ( ), , P Rp T V TH U R n n T =
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%nergy of reactants and products%nergy of reactants and products
Effect of water in products
( ) ( )H HH H
> ? > ?> ?liq > ?"ap, , , , fgV T V T U U m u
=
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%nergy of reactants and products%nergy of reactants and products
Effect of fuel in reactants
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%nthalpy of formation%nthalpy of formation
/nthalpy of products at standard
reference state
/nthalpy of reactants at standard
reference state
F F
products
,P i f iH n h=
reactants
,R i f iH n h=
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%#ample 34,%#ample 34,
Calculate the enthalpy of the products and reactants, and the
enthalpy increase and internal energy increase of the reaction, of a
stoichiometric mixture of methane and oxygen at H@9,4A K
5 H H HC> H? C? H> ?+ = +
For >H? gas!
( )F 5G@H AH H H54 9G 9E: 49 PH = + = . . .
5E5 9E .RH =
( )
59E: 49 E5 9E 94 G4 PH = + = . . .
( ) ( ) ( ) ( )
5
94 G P RV p p
U H R n n T H = = = .
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%#ample 34, 5cntd46%#ample 34, 5cntd46
For >H? liquid
( )F 5G@G AH H H9A 95 @:A HF . . .PH = + =
( )
5@:A H E5 9E 9@ GG . . .PH = + =
( ) ( ) G
59@ GG 9 G45 4 4 G H@9 4A 99A 5 . . . .VU = =
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7eating values7eating values
Heating vaueof a fuel is the magnitude of the heat of reaction at
constant pressure or at constant "olume at standard temperature for
the complete combustion of unit mass of fuel
Higher heating vauediffers from !"er heating vaueby latentheat of "aporization
( ),p
HV p TQ H= ( )
,VHV V T
Q U=
H
H
> ?
> ?p pHHV #HV fg
f
mQ Q h
m
= +
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Adiabatic flame temperatureAdiabatic flame temperature
For adiabatic constant-"olume process
FP RU U =
( ) ( ) ( ) ( ) ( )FF F
,
P P R R V T
U T U T U T U T U =
( ) ( ) ( )
,P R V TU T U T U =
i"en by initial reactant state 2TR$ p7 we
can determine the final product state 2TP$ p7
from!
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%nergy of reactants%nergy of reactants
and productsand products
R.Stone
Find molar enthalpy of JHat 5 K
( )HJ 5FFK H@EG kL kmolh =
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%#ample 343%#ample 343 5'4 8tone65'4 8tone6
n a closed combustion "essel propane 2CG>
97 and air with
an equi"alence ratio of 4.44 initially ant HAMC burn to
produce products consisting solely of carbon dioxide2C?
H7, carbon monoxide 2C?7, water 2>
H?7 and
atmospheric nitrogen.
f the heat re)ected from the "essel is 9H
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%#ample 343%#ample 343 5cntd465cntd46
Stoichiometric reaction
0ctual reaction
First law
( )G 9 H H H H HC > A ? G EEJ GC? 5> ? A G EEJ. .+ + + +
( )G 9 H H H H HC > 5 A ? G EEJ HC? C? 5> ? A 4: @GJ. . .
+ + + + +
R P P RQ U U =
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%#ample 343%#ample 343 5cntd465cntd46
*eactants at H@9 K!
( ) ( )
G 9 H HC > ? J
G 9
5 A 4: @G
4E 4A@ 5 A H 5E@ 4: @G H 59
4: G4
. .
. . . . .
.
RU U U U = + +
= + +
=
( ) ( ) ( ) ( )H H HC? C? > ? J
G 9
H 5 4: @G
H GG5 HG@ E9 EAG 5 4@9 H:: 4: @G G4 H:A
44 @E@
.
. . . . .
.
PU U U U U = + + +
= + + +
=
Bet TPbe 4E K. +henproducts at 4E K
( ) G 94F4F @E@ 4:F GF4 9AF :E9 . . .R P P RQ U U = = =
9A 9H therefore 4E K T> >
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%#ample 343%#ample 343 5cntd465cntd46
Bet TPbe [email protected] at 4@ K
( ) ( ) ( ) ( )
H H HC? C? > ? J
G 9
H 5 4: @G
H GHG @AA EG HGG 5 4@ 4 4: @G G: EH5
9A@ 5A
.
. . . . .
.
PU U U U U = + + +
= + + + =
( ) G 99A@ 5A 4:F GF4 :@@ 45@ . . .
R P P RQ U U
= = =
:@@ 9H therefore 4E 4@K T< < ? J
G 9
H 5 4: @G
H GH@ 44E E: G 5 4@5 E9 4: @G GG @9G
@GA :4E
.
. . . . .
.
PU U U U U = + + +
= + + + =
( ) G 9@GA :4E 4:F GF4 EEA G4: . . .R P P RQ U U = = =
EEA 9H so 49 K T
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%#ample 343%#ample 343 5cntd465cntd46
+o estimate the final pressure, apply the equation of state use a
basis of 4 kmol of fuel!
Dolume of reactants
For the products
pV nRT=
( )A
4 5 A 4: @G H@9
4F
. .R R
Rn RTV
p
+ += =
( )
( )A
H 4 5 4: @G 49FF4F : 55 bar
4 5 A 4: @G H@9
.
.
. .
P P Rn RT
pV R
+ + += = =
+ +
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Combustion efficiencyCombustion efficiency
( ) ( ) F Freactants products
, ,
, ,
R A P A i f i i f i
i i
H T H T m n h n h
=
Jet chemical energy release due to combustion at constant pressure
0mount of fuel energy supplied is
Combustion efficiency
( ) ( )R A P Ac
f HV
H T H T
m Q
=
f HVm Q
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Combustion efficiencyCombustion efficiency
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Chemically reacting gas mi#turesChemically reacting gas mi#tures
orking fluid in engine is a chemically reacting mixture of
gases
*eaction ne"er goes to completion /xtent to which reaction proceeds is limited by many
factors
0ctual composition of the products can be determined only
from experiment
n many cases products of combustion can be assumed to
be in chemical equilibrium
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Chemically reacting gas mi#turesChemically reacting gas mi#tures
Chemical reactions may!
be so slow that they ha"e a negligible effect on mixture
composition 2mixture composition is #frozen$7be so rapid that the mixture state changes and the
composition remains in chemical equilibrium
be one of the rate-controlling process that determine
how the composition of the mixture changes with time
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Chemical e(uilibriumChemical e(uilibrium
Consider carbon dioxide in a "essel
0t high temperature some of the C?Hmolecules diss!ciate
into C? and ?H
molecules
f the mixture of C?H, C?, and ?His in equilibrium, then
C?Hmolecules are dissociating into C? and ?Hat the same
rate as C? and ?Hmolecules are rec!mbiningin the
proportions required to satisfy the equation
H H
4C? ? C?
H+ =
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Chemical e(uilibriumChemical e(uilibrium
n combustion products of hydrocarbon fuels, the ma)or
species present at low temperatures are JH, >H?, C?H, and
?Hor C? and >H.
0t higher temperatures 2N about HH K7, these ma)orspecies dissociate and react to form additional species
H?, C?H3 .4 C?,
?>, ?H, J?, >H3 .4 >, ? 3
.4 and other species in lesser amounts.
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Condition of chemical e(uilibriumCondition of chemical e(uilibrium
y the Second Baw for chemical reaction at constant
temperature, constant pressure
0t equilibrium
FH T % & =
( ) ,p T& =
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Condition of chemical e(uilibriumCondition of chemical e(uilibrium
Consider reacting mixture of ideal gases
n concise form
y con"ention
is negati"e for reactants, and positi"e for products
Bet an amount of react with of , etc.,
and produce of , of , etc. +hese amounts
are in proportion
< < <
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Condition of chemical e(uilibriumCondition of chemical e(uilibrium
Change of ibbs energy of ideal gas mixture
where is the chemica p!tentia
For ideal gas
( ) a,
( )i ip Ti
& n =
( ), , '
i
i p T n ' i
&
n
=
( )
ln ii ip
T RT
p
= +
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9ass action la!9ass action la!
Substitution in 2a7 gi"es
( )F
F
ln Fii i
pT RT n
p
+ =
( )( )
ln ln
i i i
ip
T
& Tp (p RT RT
= = =
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9ass action la!9ass action la!
i
ip
i
p(
p
=
(pis the equilibrium constant
are partial pressures of components
is the reference pressure
are stoichiometric coefficientsi
p
ip
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%(uilibrium constant%(uilibrium constant
f equilibrium constant is known, partial pressure of
components can be determined
/quilibrium constant is function of temperature only
t is tabulated
%(uilibrium constant%(uilibrium constant
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%(uilibrium constant%(uilibrium constant
bac to ex.3.!
bac to ex.3."
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%#ample 34:%#ample 34:
0 stoichiometric mixture of C? and ?Hin a closed "essel,
initially at 4 atm and G K, is exploded. Calculate the
composition of the products of combustion at HA K and the
gas pressure
Combustion equation
From table
+hen
H H
4C? ? C?
H+ =
4log 4.55p( =
HE.A5p( =
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%#ample 34:%#ample 34:
f the degree of dissociation in the products is
2i.e., a fraction of the C?Hformed by complete combustion
is dissociated7, the product composition is
For this mixture, the number of moles of reactants nRis GOHthe number of moles of products n
Pis
( )H HC? , 4 C?, ? ,H
( )4 HPn = +
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%#ample 34:%#ample 34:
+he ideal gas law gi"es
+hus
R R R P P Pp V n RT p V n RT= =
4 HAA.AA: 4 mol
4.A G
P
P
p
n p = =
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%#ample 34:%#ample 34:
+he equilibrium relation gi"es
Jumerical solution for gi"es
( )
4 H
4 H4 HE.A
H
P
P
n pp
=
F.FFE5=
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%#ample 34:%#ample 34:
Composition of products in mole fractions
H
H
C?
C?
?
4F.9@G
F.FE4
HF.FGE
P
P
P
xn
xn
x n
= =
= =
= =
1ressure of the product mixture
A.AAA A.E: atmPp n= =
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%#ample 34-%#ample 34-
n fuel-rich combustion product mixtures, equilibrium between
the species C?H, >
H?, C?, and >
His often assumed to determine
the burned gas composition. For = 4.H , for C9>
49&air
combustion products, determine the mole fractions of the product
species at 4E K.
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%#ample 34-%#ample 34-
Solution
+he reaction relating these species 2often called the water gas
reaction7 is
From table
+hen
4log .AG
p(
=
G.G99p( =
H H HC? > C? > ?+ = +
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%#ample 34-%#ample 34-
Combustion reaction
Carbon balance gi"es!
>ydrogen balance gi"es!
?xygen balance gi"es!
( )9 49 H H H H H H4H.A
C > ? G.EEGJ C? > ? C? > [email protected]
4.H
a b c d + + + + + +
9a c+ =
H H 49b d+ =
H HF.9Ga b c+ + =
l 3
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%#ample 34-%#ample 34-
ater-gas reaction
/quilibrium equation gi"es
or
H H HC? > C? > ?+ = +
p
bc p(
ad p
=
G G99.bc
ad=
% l 3 -
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%#ample 34-%#ample 34-
Four equations are sol"ed for c
which gi"es
+he total number of moles of products is
and the mole fractions of the species in the burned gas mixture are
C?H, .@9 >
H?, .4GE C?, .A4 >
H, .HG J
H, .:@9
H [email protected] 5E.G c c + =
H.9@, A.4H, E.EH, 4.H@c a b d = = = =
[email protected] A:.Ga b c d + + + + =
8i l i
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8imultaneous reactions8imultaneous reactions
Consider mixture of J reacting gases in equilibrium
f there are C chemical elements, conser"ation of elements will
pro"ide C equations which relate the concentrations of J species
Set of 2J & C7 chemical reactions, each in equilibrium, which
includes each species at least once will pro"ide additional
equations required to determine concentration of each species in
the mixture
Complete set of equations is a coupled set of C linear and 2J & C7
nonlinear equations
+his set of equations is difficult to sol"e when 2J & C7 N H
Calculation of e(uilibrium composition for &;Calculation of e(uilibrium composition for &;
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f ( p ff ( p f
species 5 H , ?>,
>H?, C , C?, C?
H, C>
5, J,
JH , J?, J?H, J>G, >J?G, >CJ
8imultaneous reactions 5< C = &:68imultaneous reactions 5< C = &:6
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8imultaneous reactions 5< C = &:68imultaneous reactions 5< C = &:6
( ) ( )
( ) ( )
( ) ( )
( ) ( )
( ) ( )( ) ( )
( ) ( )
H 5 H
H G H
H
H H H H H
H H G H H
H H G H H
H H H
4? ? 4 C> C H> 9
H
G 4? ? H J J @
H H
4> > G J? J ? 4
H
4H> ? H> ? 5 J? J? ? 44
H
4 4 4 G
? > ?> A J> J > 4HH H H H
C? C ? : J? H>J? GJ? > ? 4G
4 4 4C? C ? E >CJ C J > 45
H H H
+
+
+ +
+ ++ + +
+ + +
%(uation of e(uilibrium%(uation of e(uilibrium
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%(uation of e(uilibrium%(uation of e(uilibrium
( )
( )
( )
( )
( )
( )
( )
H
G H
H
H H H
H H
H H
H
4 H
H 4 ? ?
G H
H G H ? ?
4 H
H G > >
H H
H H H 5 > ? > ?
4 H 4 H
H H A ?> ? >
H H : C ? C?
4 H
H E C C??
4? ? 4
H
G? ? H
H4
> > GH
H> ? H> ? 5
4 4? > ?> A
H HC? C ? :
4C? C ? E
H
( p p
( p p
( p p
( p p p
( p p p
( p p p
( p p p
=
=
=
+ =
+ =
+ =
+ =
%(uation of e(uilibrium%(uation of e(uilibrium
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( )
( )
( )
( )
( )
( )
( )
H 5
H
HH
GH H
H H G
H H
H
5 H 9 C > C>
4 H
H @ J J
4 J ? J?
4 H
H H 44 J? J??
4 H G H
G H H 4H J>J >
G H
G H H 4G J? > ? >J? J?
4 H 4 H
H H 45 C >CJJ >
C> C H> 9
4J J @
HJ? J ? 4
4J? J? ? 44
H
4 GJ> J > 4H
H HJ? H>J? GJ? > ? 4G
4 4>CJ C J > 45
H H
( p p p
( p p
( p p p
( p p p
( p p p
( p p p p
( p p p p
+ =
=
+ =
+ =
+ =
+ + =
+ + =
%(uation of e(uilibrium%(uation of e(uilibrium
Conservation of chemical elementsConservation of chemical elements
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Conservation of chemical elementsConservation of chemical elements
C ? ? J C >p p% % % % % % = = =
H 5
H G H G H H
H G H G H H
H H G G
H 5
H H
C C? C? C> >CJ
? ? ? ?> > ? >J? C? C? J? J?
? ? ? ?> > ? >J? C? C? J? J?
J? J J J? J> >J? >CJ
C C? C? C> >CJ
H G G H H
H G G H H
H
H H 5
p
p
p
H H )H H ) *
p p p p p
p p p p p p p p p p
p p p p p p p p p p
p p p p p p p
p p p p p
p p p p p
+ + + +=
+ + + + + + + + +
+ + + + + + + + +=
+ + + + + +
+ + + +=
+ + + +5 G G
H G H H H 5
H H G G
? ? ? C C? C? C> J
J J? J? J> >J? >CJ
G
H +H H+) H*+
H H )H H )
p p p
p p p p p p p p p p p p p
p p p p p p
+ + +
= + + + + + + + + + + + +
+ + + + +
where!
8ome results8ome results
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8ome results8ome results
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%ff t f iti%ff t f iti
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%ffect of pressure on composition%ffect of pressure on composition
F F F
i i i
iii
i i p
i i i
p p px x (
p p p
= = =
f changes in pressure ha"e no effect on the
composition.
f 2dissociation reaction7, then the mole
fractions of the dissociation products decrease as pressureincreases.
f 2recombination reaction7, the con"erse is true.
ii
=i
i
>
i