diesel engine fundamentals 3 - wordpress.com · 2013. 9. 8. · • sequential turbocharging •...
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11
TurbochargingTurbocharging
22
Why turbocharging ?Why turbocharging ?
σληηηηη c
cc
L
tdqcombmtrapmeP
TRhP ××××××=
• Obtain more power from a cylinder of given size
• To increase mass of air increase intake manifold pressure and
decrease temperature
33
Cylinder pressures in naturally aspirated (1Cylinder pressures in naturally aspirated (1--22--33--44--5) 5) and turbocharged (1and turbocharged (1--22--33’’--44’’--55’’) engines) engines
44
Improvements in power: weight ratio due to Improvements in power: weight ratio due to turbochargersturbochargers
55
Why turbocharging ?Why turbocharging ?
66
Turbocharger configurationsTurbocharger configurations
Compressors:•Axial flow (very rare)•Centrifugal
• vane less diffuser• vaned diffuser
Turbines:•Radial (with or without guide vanes)•Mixed flow (with or without guide vanes)•Axial flow (guide vanes essential)
Turbine mode:•Constant pressure•Pulsed
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TurbochargingTurbocharging
88
Turbocharger with axialTurbocharger with axial--flow turbineflow turbine
99
Variable inlet guide vanes Variable inlet guide vanes for a radial flow for a radial flow turbineturbine
The ability to vary the throat area provides good turbine/compressor matching over a much wider operating range than is possible with a fixed geometry.
1010
Ideal turbocharged limiting pressure cycleIdeal turbocharged limiting pressure cycle
Options• Turbine acts as a flow restrictor creating a constant pressure P7 in the flow duct
• Available energy = 7-8-10-11• Turbine placed very close to the exhaust valve
• available energy = 5-6-7-8
1111
Modes of turbocharging (1)Modes of turbocharging (1)•• Constant pressureConstant pressure
–– Exhaust manifold with large volumeExhaust manifold with large volume
–– Steady flow of exhaust into the turbineSteady flow of exhaust into the turbine
–– Matched for optimum efficiency at specified engine Matched for optimum efficiency at specified engine conditioncondition
–– Not responsive to sudden load changesNot responsive to sudden load changes
–– Pulse energy 5Pulse energy 5--77--13 cannot be used13 cannot be used
•• PulsedPulsed–– Not pure pulse but constant pressure + pulseNot pure pulse but constant pressure + pulse
–– High energy available at turbine inletHigh energy available at turbine inlet
–– Good turbocharger accelerationGood turbocharger acceleration
–– Good performance at low speeds and loadGood performance at low speeds and load
–– Poor turbine efficiency due to unsteady flowPoor turbine efficiency due to unsteady flow
–– Complex exhaust manifoldComplex exhaust manifold
–– Possible pressure wave reflection problemsPossible pressure wave reflection problems
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Modes of turbocharging (3)Modes of turbocharging (3)
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Modes of turbocharging (2)Modes of turbocharging (2)
1414
Efficiency definitions (1a) Efficiency definitions (1a) –– isentropic efficiencyisentropic efficiency
Compressor:Compressor:
( )( )
2 12 1
2 1 2 1
(for a perfect gas, ).sisen sC p
Cp T TW h h h C TW h h Cp T T
η−−
= = = =− −
1
21
12 2
21 1
1
1 so
1
sC
PPT PTT PT
γγ
γγ
η
−
−⎛ ⎞
−⎜ ⎟⎛ ⎞ ⎝ ⎠= =⎜ ⎟⎝ ⎠ −
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Efficiency definitions (1b) Efficiency definitions (1b) –– isentropic efficiencyisentropic efficiency
Turbine:Turbine:
4
3 4 31
3 44
3
1
1
Tisen s
TT T TW
W T T PP
γγ
η −
−−
= = =− ⎛ ⎞
− ⎜ ⎟⎝ ⎠
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Turbocharger cycle analysis (1)Turbocharger cycle analysis (1)
1
, 2 1 , 1 2, 2 1
1
Compressor work:
C ( ) CC ( ) 1a p a s a p a
C a p aC C
m T T m T pW m T Tp
γγ
η η
−⎡ ⎤− ⎛ ⎞⎢ ⎥= − = = −⎜ ⎟⎢ ⎥⎝ ⎠⎢ ⎥⎣ ⎦
& && &
1
4, 4 3 , 4 3 , 3
3
Turbine work:
C ( ) C ( ) C 1T e p e e p e s T e p epW m T T m T T m Tp
γγ
η
−⎡ ⎤⎛ ⎞⎢ ⎥= − = − = −⎜ ⎟⎢ ⎥⎝ ⎠⎢ ⎥⎣ ⎦
& & & &
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Turbocharger cycle analysis (2)Turbocharger cycle analysis (2)
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Turbocharger cycle analysis (3)Turbocharger cycle analysis (3)
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Turbocharger cycle analysis (4)Turbocharger cycle analysis (4)
12
12 1
1 )]11(1[ γγ
γγδβχτη
−
−−+=tur
ctccomp
rr
β = pulsating pressure correction
δ = (1 + (1/σλ))
σ = stoichiometric air to fuel ratio
λ = excess air ratio
τ = driving temperature ratio
ηtc = overall turbocharger efficiency = ηcomp* ηtur * ηm
X = ratio of specific heat
rcomp = compressor pressure ratio
rtur = turbine pressure ratio
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Turbocharger cycle analysis (5)Turbocharger cycle analysis (5)
1 1.5 2 2.5 3 3.5 41
1.5
2
2.5
3
3.5
4
4.5
5Relationship between charge air and turbine pressure ratio, Overall efficiency = 0.63
Com
pres
sor
pres
sure
rat
io
Turbine pressure ratio
* Iran Noahx Iran Najmo Iran Noor Test Bed Trial 75%+ Iran Noor Test Bed Trial 85%
temp.ratio = 2.15temp.ratio = 2.30temp.ratio = 2.5temp.ratio = 2.64
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Turbocharger cycle analysis (6)Turbocharger cycle analysis (6)
1 1.5 2 2.5 3 3.5 41
1.5
2
2.5
3
3.5
4
4.5
Com
pres
sor
pres
sure
rat
iooverall efficiency 0.60
1 1.5 2 2.5 3 3.5 41
1.5
2
2.5
3
3.5
4
4.5
Com
pres
sor
pres
sure
rat
io
Turbine pressure ratio
Relationship between charge air and turbine pressure ratio, Overall eff. = 0.60 & 0.65
* Iran Noahx Iran Najmo Iran Noor Test Bed Trial 75%+ Iran Noor Test Bed Trial 85%
overall efficiency 0.65
2222
Turbocharger cycle analysis (7)Turbocharger cycle analysis (7)
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Turbocharger performance (1)Turbocharger performance (1)
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Turbocharger cycle analysis (2)Turbocharger cycle analysis (2)
)(2)(22
)(
21
..
.
eiei
ei
CRCRmNCCmNRNTP
CCmF
+=+==
+=
πππ
)()22( '.
21
.
ibiebeei wCwCmCNRCNRmP −=+= ππ
ebe
we
we
we
fCC
CC
βμ
cot
''
−==
2.
2..
'.
)( DNmCmwCmwCmP beebeebe πμμμ ====
2.
1
1
)(
)1(
DNm
rTC comppis
πμη
γγ
−=
−
ηtc = overall turbocharger efficiency = ηcomp* ηtur * ηm
2525
InterInter--cooling (1)cooling (1)
2 3
2 1
T TT T
ε −=
−
( )3 2 11T T Tε ε= − +
1
22 1
1
11 1C
PT TP
γγ
η
−⎡ ⎤⎛ ⎞⎛ ⎞⎢ ⎥⎜ ⎟= + −⎜ ⎟⎢ ⎥⎜ ⎟⎝ ⎠⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦
( ) ( )1 1
3 2 2
1 1 1
111 1 1 1 1C C
T P PT P P
γ γγ γε
ε εη η
− −⎡ ⎤⎛ ⎞ ⎛ ⎞−⎛ ⎞ ⎛ ⎞⎢ ⎥⎜ ⎟ ⎜ ⎟= + − + − = + −⎜ ⎟ ⎜ ⎟⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦
,
( )11
3 3 31 2
1 1 3 1 1
11 1
C
P PT PP T P P
γγερ
ρ η
−−⎡ ⎤⎛ ⎞− ⎛ ⎞⎢ ⎥⎜ ⎟= = + −⎜ ⎟⎢ ⎥⎜ ⎟⎝ ⎠⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦
2626
Intercooling (2)Intercooling (2)
• Intercooler increases density of air entering engine – increases engine power.2Mass of air drawn into each cylinder a sw volm Vρ η=
2727
Advanced turbocharging conceptsAdvanced turbocharging concepts
•• Waste gate and/or blow offWaste gate and/or blow off•• Power take offPower take off•• Variable geometryVariable geometry•• Sequential turbochargingSequential turbocharging•• Two stage turbochargingTwo stage turbocharging
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Blow offBlow off
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Sequential turbochargingSequential turbocharging
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Two stage turbochargingTwo stage turbocharging