3 Thermochemistry of Fuel-Air Mixtures

7/25/2019 3 Thermochemistry of Fuel-Air Mixtures

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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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Single bond ring hydrocarbons

%nsaturated ring can be broken andadditional hydrogen added

Cyclopropane, cyclobutane,

cyclopentane, etc.


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?pen-chain hydrocarbons containing double

bond

%nsaturated

/thylene, propylene, butylene, etc.

Same formula as cycloparaffins, butdifferent structure


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?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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Effect of water in products

( ) ( )H HH H

> ? > ?> ?liq > ?"ap, , , , fgV T V T U U m u

=


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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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*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> >


51/86


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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+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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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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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

= +


63/86

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

= = =


64/86

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


65/86

%(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



66/86


bac to ex.3.!

bac to ex.3."


67/86

%#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( =


68/86


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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+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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+he equilibrium relation gi"es

Jumerical solution for gi"es

( )

4 H

4 H4 HE.A

H

P

P

n pp

=

F.FFE5=


71/86


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= =


72/86

%#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.


73/86


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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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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ater-gas reaction

/quilibrium equation gi"es

or

H H HC? > C? > ?+ = +

p

bc p(

ad p

=

G G99.bc

ad=

% l 3 -


76/86


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


77/86

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 &;


78/86

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


80/86


( )

( )

( )

( )

( )

( )

( )

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

=

=

=

+ =

+ =

+ =

+ =



81/86

( )

( )

( )

( )

( )

( )

( )

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

+ =

=

+ =

+ =

+ =

+ + =

+ + =


Conservation of chemical elementsConservation of chemical elements


82/86

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


83/86

8ome results8ome results


84/86


85/86

%ff t f iti%ff t f iti


86/86

%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

3 Thermochemistry of Fuel-Air Mixtures

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