1 Adiabatic Flame Temperature Reaction Q W P 2 =P a T 2 =T a Consider the case where the cylinder is...
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Transcript of 1 Adiabatic Flame Temperature Reaction Q W P 2 =P a T 2 =T a Consider the case where the cylinder is...
1
Adiabatic Flame Temperature
ReactionQ
W
P2=Pa
T2=Ta
Consider the case where the cylinder is perfectly insulated so the process isadiabatic (Q = 0)
)()(
0)()(
1
Rii
Paii
RRii
Ppii
ThnThn
ThnThnQ
For a constant pressure process, the final products temperature, Ta, is known as the adiabatic flame temperature (AFT).
For a given reaction where the ni’s are known for both the reactants and the products, Ta can be calculated explicitly.
2
Ta,
Constant Pressure Adiabatic Flame Temperaturew/products at equilibrium
3
Constant Pressure Adiabatic Flame Temperaturew/products at equilibrium
4
Constant Volume Adiabatic Flame Temperature
ReactionQ
W
P2=PCV
T2=Ta
Consider the case where the piston is fixed and the cylinder is perfectly insulated so the process is adiabatic (Q = 0)
)()(
0)()(
1
Rii
Paii
RRii
Ppii
TunTun
TunTunQ
Note h = u + pv = u + RT, so
T) R)(Th(nTRThnR
iiP
aii 1))((
5
i
a
R
p
i
CV
R
p
R
p
R
p
p
pp
R
RR
PR
T
T
n
n
P
P
T
T
n
n
P
P
P
TRn
P
TRn
VV
Constant Volume Combustion Pressure
Assuming ideal gas behavior:
For large HCs the mole ratio term is small, e.g., for stoichiometric octaneair
22222188 4798)76.3(5.12 NOHCONOHC
i
a
i
a
i
a
R
p
i
CV
T
T
T
T
T
T
n
n
P
P06.1
5.60
64
For stoichiometric octane-air Ta is 2266K so PCV/Pi = 8.1
6
• One can calculate the AFT for the above stoichiometric reaction where the products are at equilibrium.
• Note dissociation in the products will result in a lower AFT since dissociation reactions are endothermic.
Adiabatic Flame Temperaturew/Products at Equilibrium
kNjNOiOHhOgH
fHeCOdOcNObHaCONOHC
)76.3)(4
( 2222222
• Computer programs are used for these calculations