enhancing flexibility and transient capability of the diesel engine

AUTOMOTIVE RESEARCH CENTER

THE UNIVERSITY OF MICHIGAN

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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



arcThermal Network Modeling -Thermal Network Modeling -

MOTIVATIONMOTIVATION• Wall temperature variations during engine speed and

load transient

475

480

485

490

495

500

505

510

0 5 10 15 20 25 30

Pis

ton

Sur

face

Te

mp.

(K

)

Time (s)

Cyclicfluctuationsof wall temperatures



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.

0

500

1000

1500

2000

0 100 200 300 400 500 600 700

Te

mp

era

ture

(K

)

Crank Angle (deg)

Piston Surface

Mean Gas

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



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

2000

2500

3000

3500

4000

4500

5000

5500

6000

0

500

1000

1500

2000

800 1000 1200 1400 1600 1800 2000 2200

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

)

Engine Speed (rpm)

Po

we

r (k

W)



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VEHICLE ACCELERATIONVEHICLE ACCELERATION

Vehicle Acceleration from stand still for 40 seconds (Conventional Engine)

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40

Ro

tati

on

al

Sp

ee

d

(ra

d/s

)

Time (s)

Engine

Transmission InTransmission Out

Drive Shaft

0

5000

10000

15000

20000

25000

30000

0 5 10 15 20 25 30 35 40

Sh

aft

T

orq

ue

(N

m)

Time (s)

Engine

Sprocket

TorqueConverter

Out



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Transient Temperature VariationsTransient Temperature Variations

450

500

550

600

650

700

750

0 5 10 15 20 25 30

Pis

ton

S

urf

ace

T

em

p.

(K)

Time (s)

Conventional Engine

LHR Engine (1.0 mm Coating)

800

810

820

830

840

850

860

870

880

0 5 10 15 20 25 30 35 40

Exh

au

st

Ga

s T

em

pe

ratu

re

(K)

Time (s)


Conventional Engine



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Boost Pressure Histories -Boost Pressure Histories -Conventional vs. LHRConventional vs. LHR

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40

Bo

ost

P

ress

ure

(k

Pa

)

Time (s)


Conventional Engine



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System Response System Response

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40

LHR Engine

Conventional Engine

Ve

hic

le

Sp

ee

d

(Mile

/h)

Time (s)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20 25 30

Cyl

ind

er

Eq

uiv

ale

nce

R

ati

o

(-)

Time (s)

LHR Engine

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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1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

0 5 10 15

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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1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

0 5 10 15

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

1

1 . 2

1 . 4

1 . 6

1 . 8

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=1.0LIn

take

Man

ifold

Pre

ssur

e (b

ar)

Engine Speed (RPM)

1

1 . 2

1 . 4

1 . 6

1 . 8

2

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

1 0

2 0

3 0

4 0

5 0

6 0

1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0


Pow

er (

kW)

Engine Speed (RPM)

2 0 0

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


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.

enhancing flexibility and transient capability of the diesel engine

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