Enhancing Flexibility and Transient Capability of the Diesel Engine
Transcript of Enhancing Flexibility and Transient Capability of the Diesel Engine
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Enhancing Flexibility and Enhancing Flexibility and Transient Capability of the Transient Capability of the
Diesel Engine System SimulationDiesel Engine System Simulation
ARC Conference
May 19-20, 1998
Ann Arbor, Michigan
Zoran FilipiDennis Assanis
Dohoy JungGeorge Delagrammatikas
Jennifer LiedtkeDavid Reyes
Doug RosenbaumAlejandro Sales
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ACKNOWLEDGEMENTSACKNOWLEDGEMENTS
• National Automotive Center (NAC) located within the US Army TARDEC for technical and financial support.
• The University of Wisconsin team has contributed the MATLAB vehicle template and component models for the drivetrain sub-system.
• Guoqing Zhang and Xiaoliu Liu for initial contributions to implementation of the V12 diesel engine simulation in Matlab-SIMULINK.
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OUTLINEOUTLINE
• Introduction:- The need for enhanced flexibilty and transient capability of
the diesel engine simulation in the context of Powertrain System modeling.
• Thermal network modeling of engine heat rejection.
• Assessment of the potential of the Low Heat Rejection (LHR) tank engine.
• Virtual diesel engine for the HEV.
• Scaling of the complete diesel engine system for optimization studies.
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FlexibilityFlexibility
• Matlab-SIMULINK environment allows easy reconfiguration of the engine and powertrain system, e.g. variation of the number of cylinders, configuration of the driveline (4x2, 4x4, 6x6 ...).
• Variation of the number of cylinders or cylinder size requires resizing of external diesel engine system components.
• Turbomachinery is modeled using digitized maps, hence for every variation of engine size new set of maps is needed.
• Control devices, such as wastegates also need to be scaled.
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Need to Enhance Transient CapabilityNeed to Enhance Transient Capability
• Rapid changes of engine speed and load initiate very dramatic thermal transients
• Combustion chamber thermal condition affects volumetric efficiency, heat rejection, combustion and friction in a diesel engine
• Transient heat transfer model needed to enhance simulations ability to predict system response and vehicle performance
• Enhanced heat transfer model essential for evaluation of alternative designs, such as Low Heat Rejection (LHR) engines
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arcThermal Network Modeling -Thermal Network Modeling -
MOTIVATIONMOTIVATION• Wall temperature variations during engine speed and
load transient
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Pis
ton
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face
Te
mp.
(K
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Time (s)
Cyclicfluctuationsof wall temperatures
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arc Thermal Behavior of the Thermal Behavior of the LHR EngineLHR Engine
• Cyclic surface temperature variations of conventional metal engines : 5 to 15 K
• Cyclic surface temperature variations of LHR engines: 100 to 150 K (Zirconia Coating)
• Larger temperature swing of LHR engine requires the capability for transient surface temperature prediction.
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ture
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Crank Angle (deg)
Piston Surface
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Conventional Eng.LHR Eng. (1.0 mm Coating)
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Modeling IssuesModeling Issues
• Need fidelity and computational efficiency
• Finite Element Methods- High fidelity- Computationally intensive- Need to generate meshes for every new design
• Thermal Network model provides a good compromise:- High fidelity of global component temperature predictions- much less computational effort than FEA methods
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Lumped Capacitance MethodLumped Capacitance Method
• Sub-system: cylinder head, piston, liner, oil reservoir, coolant in head and block.
• Combustion chamber walls are divided into 8 sublayers based on Biot Number criterion:
Liner
Water Jacket
Head
Oil Reservoir
Oil HeatExchanger
Water Jacket
Piston
Head HeatExchanger
Block HeatExchanger
Cylinder Gas
BihL
kc= << 1
h : convection coef.Lc : characteristic lengthk : conductivity
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LUMPED CAPACITANCE METHODLUMPED CAPACITANCE METHOD(Mathematical Formulation)(Mathematical Formulation)
• Conservation of Energy
T T
RQ Q m c
T T
tjp
ip
i jp
j
condconvrad
sourcepsource
kpk
i v iip
ip−
∑ + ∑ − ∑ =−+
,
..
.
sin
sin
,
1
∆
• Thermal Resistances
RL
kA=
Rr r
Hk= ln( / )2 1
2π
RhAs
= 1
T :Nodal Temp. R : Thermal Resistance Q : Heat Source or Sink m : mass Cv : Const. Vol. Specific Heat i, j : node p, p+1 : Time step ∆t : Time Step Size
(Axial Conduction)
(Radial Conduction)
(Convection)
L : Distance between Nodes k : Conductivity A : Cross Sectional Area r1, r2 : Inner and Outer Radii H : Cylinder Height h : Convection Coef. As : Surface Area
Heat Heat fluxfluxtermterm
CapacitanceCapacitancetermterm
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arcVirtual Tank EngineVirtual Tank Engine
• Hypothetical V12 Diesel Engine
• 4-Stroke DI Diesel
• 2 Turbochargers
• 2 Intercoolers
• Bore = 6.25 in (15.9 cm)
• Stroke = 6.25 in (15.9 cm)
• CR = 15
• Predicted Power: 1440 HP@2100 rpm
INTER-COOLER
FUELSYSTEM
AirExhaustgas
W.
TC CT
Air Exhaustgas
INTER-COOLER
V12 ENGINE
IM
IM
EM
EM
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Engine System in SIMULINKEngine System in SIMULINKPowerSim
I/M 1
I/M 2
E/M 1
E/M 2Cylinders
Heat Trans.Model
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The Effect of Wall Insulation on The Effect of Wall Insulation on System Steady-State andSystem Steady-State and
Transient PerformanceTransient Performance
• Steady-state performance at full load
• Acceleration from stand still with 100% driver’s demand after engine has been warmed up
• Three virtual engine versions:
- Conventional Engine- LHR Engine (0.5 mm Zirconia Coating)- LHR Engine (1.0 mm Zirconia Coating)
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Engine Performance Comparison - Engine Performance Comparison - Conventional vs. LHR EngineConventional vs. LHR Engine
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Conventional Eng.LHR Eng. (0.5 mm Coating)LHR Eng. (1.0 mm Coating)Cummins Eng.
Conventional Eng.LHR Eng. (0.5 mm Coating)LHR Eng. (1.0 mm Coating)Cummins Eng.
To
rqu
e
(Nm
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Engine Speed (rpm)
Po
we
r (k
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VEHICLE ACCELERATIONVEHICLE ACCELERATION
Vehicle Acceleration from stand still for 40 seconds (Conventional Engine)
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tati
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ee
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Engine
Transmission InTransmission Out
Drive Shaft
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Sh
aft
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orq
ue
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m)
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Engine
Sprocket
TorqueConverter
Out
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Transient Temperature VariationsTransient Temperature Variations
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urf
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LHR Engine (1.0 mm Coating)
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au
st
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ratu
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Time (s)
LHR Engine (1.0 mm Coating)
Conventional Engine
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Boost Pressure Histories -Boost Pressure Histories -Conventional vs. LHRConventional vs. LHR
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Conventional Engine
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System Response System Response
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Fuel control based on manifold pressure
Comparison of Vehicle Speeds F/A Equivalence Ratio in the LHR Cylinder
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Enhancing Flexibility for Integration Enhancing Flexibility for Integration with Optimization Codeswith Optimization Codes
• Engine system needs to be simulated within the range, e.g. 1.0 to 1.9 liter displacement.
• External components have to scaled accordingly, including turbomachinery.
• Continuous variation of size required throughout the range
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Turbocharged Diesel EngineTurbocharged Diesel Enginefor the HEVfor the HEV
• Baseline engine : VW 1.9 L TDI
• Wide engine speed range requires boost pressure control - wastegate
FUELSYSTEM
4CYL ENGINE
IM
EM
INTER-COOLER
TC
ATMOSPHERE
WGP
ress
ure
Rat
io
Mass flow rate
Simulated engine operating line
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Scaling of Engine GeometryScaling of Engine Geometry
• Express the following as a function of Bore :- Stroke- Connecting rod length- Valve/port diameters and maximum valve lifts- Manifold volumes
• Assume scaled engine will have same S/B ratio as the baseline engine
• Find new Bore as a function of new displacement. i.e:
• Calculate new engine geometry as a function of B new
BB
S
V
Inewold
old
displ new
cylinders= ( )_ /4 1 3
Π
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Wastegate ModelingWastegate Modeling
• Wastegate valve dynamics
• m, b, S, A v, Adfgm , Fprel- design parameters
• Pressures at every instant supplied by the engine simulation
m z b z Sz p p A p p A Fexman back v cntrl atm dfgm prel
.. .( ) ( )+ + = − + − −
TURBUNEINLET SIDE
PEXMAN
PBACK
Diaphragm
Pcontrol (boost)
PatmSpring
Needs to be scaled along with engine geometry
A v new/A v old = A dfgmnew/A dfgmold =Vnew/Vold
Spring stiffness and F prel scale linearly with Adfgm new
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Overview of Turbomachinery Overview of Turbomachinery Scaling MethodologyScaling Methodology
m RT
p D
T
Tf
ND
RT
p
p
m
D01
012
0
01 01
02
01
. .
, , ( , , , )ηµ
γ∆ =
N D N D1 1 2 2=
m
D
m
D1
12
2
22
. .
= η η1 2=
V
Vdispl new
displ old
_
_= α
m
m
2
1
.
. = α D
D
N
N1
2
2
1
1= =α
samenegligable
same
Based on non-dimensional representation of Compressor and Turbine Characteristics
DimensionalAnalysis
Assuming
Scaling factor
hence
Scaleing ofcharacteristics
N max1 > N max 1.9
;
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Simulated Intake and ExhaustSimulated Intake and ExhaustManifold Pressure for the Range of Manifold Pressure for the Range of
Turbocharged EnginesTurbocharged Engines
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1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0
Displacement=1.9LDisplacement=1.8LDisplacement=1.7LDisplacement=1.6LDisplacement=1.5LDisplacement=1.4LDisplacement=1.3LDisplacement=1.2LDisplacement=1.1LDisplacement=1.0LIn
take
Man
ifold
Pre
ssur
e (b
ar)
Engine Speed (RPM)
1
1 . 2
1 . 4
1 . 6
1 . 8
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2 . 2
1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0
Displacement=1.9LDisplacement=1.8LDisplacement=1.7LDisplacement=1.6LDisplacement=1.5LDisplacement=1.4LDisplacement=1.3LDisplacement=1.2LDisplacement=1.1LDisplacement=1.0L
Exh
aust
Man
ifold
Pre
ssur
e (b
ar)
Engine Speed (RPM)
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Simulated Power Output and BSFC for Simulated Power Output and BSFC for the Range of Turbocharged Enginesthe Range of Turbocharged Engines
0
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2 0
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1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0
Displacement=1.9LDisplacement=1.8LDisplacement=1.7LDisplacement=1.6LDisplacement=1.5LDisplacement=1.4LDisplacement=1.3LDisplacement=1.2LDisplacement=1.1LDisplacement=1.0L
Pow
er (
kW)
Engine Speed (RPM)
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2 1 0
2 2 0
2 3 0
2 4 0
2 5 0
2 6 0
2 7 0
1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0
Displacement=1.9LDisplacement=1.8LDisplacement=1.7LDisplacement=1.6LDisplacement=1.5LDisplacement=1.4LDisplacement=1.3LDisplacement=1.2LDisplacement=1.1LDisplacement=1.0L
BS
FC
(g
/kW
-hr)
Engine Speed (RPM)
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SummarySummary
• Thermal network modeling allows prediction of the effect of the variation of engine component wall temperatures on system response and vehicle performance
• Thermal network model critical for evaluation of the LHR concept for tank propulsion
• Lumped capacitance model provides fidelity at low cost
• Turbomachinery scaling methodology enhances the flexibility of the system simulation and allows continuous variations of engine size in optimization studies.
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Future ChallengesFuture Challenges
• Extend the thermal network model to include engine external components, e.g. manifolds.
• Investigate engine transients under extreme conditions, i.e.:
- cold start and engine acceleration at very low temperatures- system response at very high ambient temperatures- high altitude operation
• Develop techniques for modeling variable geometry turbines/compressors.
• Investigate the effect of alternative turbocharging techniques, e.g. sequential turbocharging, supercharging + turbocharging etc.