Waste-Gated Turbochargers Behaviour Under Steady · PDF fileWaste-Gated Turbochargers Behaviour Under Steady and Unsteady Turbine Operation ... 2nd April 2008 12 ... C compressor PC

1

Waste-Gated Turbochargers Behaviour

Under Steady and Unsteady Turbine Operation

Advanced Charging & Downsizing ConceptsAdvanced Charging & Downsizing ConceptsStuttgart, Germany, 31st March- 2nd April, 2008

Silvia Marelli

Internal Combustion Engines Group (ICEG)Department of Thermal Machines, Energy Systems and Transportation (DIMSET)

University of Genoa – Italy

Silvia Marelli – University of Genoa – Advanced Charging & Downsizing Concepts – 2nd April 2008 2

ContentsContents

Introduction

Exhaust turbochargers testing

Steady flow results

Unsteady flow analysis

Conclusions


ContentsContents

Introduction


Steady flow results


Conclusions


BackgroundBackground

The reduction of fuel consumption and CO2 emissions has recently becomea fundamental target for automotive propulsion systems together with lowexhaust emissions

Automotive diesel engines have been substantially improved in recentyears, due to the introduction of breakthrough technologies (electroniccontrolled FIS, VGT, etc), even if a further reduction of exhaust emissions(especially NOX and particulate) is required to comply with forthcoming EUand US regulations

The spark ignition (SI) engine needs today to significantly reduce fuelconsumption and CO2 emissions (especially at part load) while maintaininghigh specific power, very low exhaust emissions (3-ways catalyst) andexcellent vehicle driveability

To achieve this goal, different solutions can be addressed in a short period: alternative fuels (CNG, LPG, ethanol, etc)

engine downsizing and turbocharging

variable valve actuation (VVA)

direct gasoline injection (with stoichiometric combustion)

Turbocharging is therefore becoming a key technology for both gasolineand diesel automotive engines


Turbocharging the automotive SI engineTurbocharging the automotive SI engine

The successful application of exhaust turbocharging to downsized SIengines has to face several problems: transient response

low end torque

engine exhaust gas temperature (catalyst light-off, VG turbines application)

Variable geometry turbines are today widely used in diesel turbochargingbut their application to SI engines is difficult due to the harsh thermalexhaust environment

A waste-gate valve (pneumatically or electrically driven) is usually fitted asa turbocharger control system in SI applications, due to its effectiveness,low cost and ability to work at high gas temperatures

In order to optimize engine-turbocharger matching, turbine performancewhen the waste-gate valve is partially or totally opened should be known

Unfortunately, this information (which is a fundamental input for theoreticalsimulation models) is usually not provided by turbocharger manufacturer

A dedicated investigation on the turbocharger behavior in the openedwaste-gate region is therefore desirable, extended both to steady state andto the typically unsteady flow conditions occurring in automotive engines


Automotive turbochargers investigation topicsAutomotive turbochargers investigation topics

Definition of compressor and turbine maps in an extended range

Evaluation of unsteady flow turbine performance

Analysis of turbocharger regulating systems behaviour

Interactions between the turbocharger and the engine intake andexhaust system

Development of unsteady flow performance prediction procedures

Dedicated test facilities are particularly suitableto investigate turbocharger performance

independently of the engine


ContentsContents

Introduction


Steady flow results


Conclusions


Turbocharger test facility options (1/2)Turbocharger test facility options (1/2)

Air temperature level at the turbine inlet “hot air” test rigs

• combustion chamber• high temperature transducers

“cold air” test rigs• electrical air heater• lower absolute turbocharger rotational speed

Turbine power absorption device turbocharger compressor

• limited operating range• high rotational speed allowed• need of specific experimental techniques/devices to

extend turbine curves• information on the compressor side of TC available

high speed dynamometer• extended measurement of turbine characteristics• complexity of design• restricted rotational speed range• low flexibility• very sensitive measuring equipment required


Turbocharger test facility options (2/2)Turbocharger test facility options (2/2)

Flow characteristics at the turbine inlet Steady flow

• definition of turbocharger maps• baseline analysis on TC regulating device behaviour

Unsteady flow• further complexity of the test facility• need of a pulse generator system• use of high speed measuring systems• information on the effect of unsteady flow parameters

on turbine performance Partial and unequal admission (tests on two-entry turbines)


Schematic diagram of typical TC test rigSchematic diagram of typical TC test rig

Ref.: D.E. Winterbone and R.J. Pearson, Design Techniques for Engine Manifolds: Wave Action Methods for IC Engines, 1999


The UNIGE test facilityThe UNIGE test facility

Development of “cold” air tests (max 400K) on I/E components and subassemblies(particularly automotive turbochargers)

Two independent feeding lines areavailable for the TC turbine andcompressor (acting as a dynamometer)

Suitable experimental techniques are usedto extend the definition of turbinecharacteristics

Turbine performance can also beinvestigated under unsteady flow andtransient conditions by using two differentpulse generator systems

AF air filter LM laminar flow meterAH air heater LC lubricating circuitAR air receiver PC pressure controlC compressor SC screw compressorDC dynamic compressor T turbineFM flow meter


Rotating valves pulse generator systemRotating valves pulse generator system

Turbocharger T C

Rotating valves

Compressor air supply

Turbine air supplya)Plenum

Designed to perform parametric studieson the effect of the main unsteady flowparameters

Tests on single and two-entry turbinesallowed

Pulsating flow generated by diametral slotrotating valves

Easy control of pressure pulse parameters(amplitude, mean value) at each turbineentry

Pulse frequency can be adjusted in thetypical range of automotive I/E circuits(10-200 Hz)

Unequal admission and not-phasedpulsating flow conditions can bereproduced when testing two-entryturbines


Cylinder head pulse generator systemCylinder head pulse generator system

Turbocharger

Compressor air supply

Flow distributor

Turbine air supply

Manifold

Engine head

T C

Plenum Designed to investigate engine exhaustsubsystem behaviour in unsteady flowconditions, including the effect of: circuit geometry valve actuation strategies

Three main components downstream ofthe damping plenum: flow distributor (designed to reproduce

the engine cylinder block) motor-driven cylinder head (fitted with

a fully flexible VVA system) engine exhaust manifold (different

configurations) Dedicated throttle valves in the flow

distributor to reproduce engine loadtransients


Measuring system and data processing (1/2)Measuring system and data processing (1/2)

Measurement of: pressure (average and instantaneous

static levels) temperature turbine and compressor mass flow rate turbocharger rotational speed pulse frequency

Measurements performed thoroughan automatic data acquisition systemcontrolled by PC using dedicatedprocedures developed in LabVIEW®

environment Specific analysis tools for post-

processing of instantaneous signals(different filtering and averagingtechniques available)

Transduce rssignals

Gould OS-4020

In strumentB

us(IE EE

488)

IOTECH ADC 488AD converter

NI PCI-6110PersonalComputer

interfaceGP-IB

Dig. stor. oscill.

Digital counter

Data acquis. unit

HP-5316A

HP-3497A

volmeterDigital

NI PCI-6250M


Measuring system and data processing (2/2)Measuring system and data processing (2/2)

Station 1: compressor inlet section Station 2: compressor outlet section Station 3: turbine upstream section Station 4: turbine downstream section Station 5: turbine mass flow rate

estimated by a laminar flow meter Station 6: compressor mass flow rate

estimated by a sharp edged orifice Station 7: measuring stations on

manifold branchessect. 4

RVRV

AR

LC

sect. 3

T C

CBCH

AR

FM

AH

PULSE GENERATOR SYSTEMS

LM

PC AF

DC

AF

AF PC

SC SC SC

AR

sect. 6

sect. 5

sect. 2

sect. 1

sect. 7

AF air filter FM flow meterAH air heater LM laminar flow meterAR air receiver LC lubricating circuitC compressor PC pressure controlCB cylinder block RV rotating valveCH cylinder head (VVA) SC screw compressorDC dynamic compressor T turbine


ContentsContents

Introduction


Steady flow results


Conclusions


Mass flow sensitivity to wasteMass flow sensitivity to waste--gate openinggate opening

Higher sensitivity to the turbineregulating system for lower waste-gate settings: 95 per cent of the total mass

flow rate increase is achievedwhen the waste-gate opening(connecting roddisplacement) is about 50 percent

a very little driving roddisplacement (about 5 percent, i.e., 1.5 mm) results ina substantial swallowingincrease

Waste-gate mass flow rate increase

1000100

0

AndAnd

Andnd

MM

MMAdvanced turbochargercontrol needs a veryaccurate waste-gate

driving system

0

20

40

60

80

100

0 20 40 60 80 100Waste-gate opening degree [%]

Was

te-g

ate

mas

sfl

owra

tein

crea

se[%

]

3

4000T

n rpmT K

1.32tTS


Turbine steady flow characteristicsTurbine steady flow characteristics

The investigation was performed on a small automotive turbocharger (IHIRHF3), matched to a downsized SI engine (4-cylinder, 1.4 litres)

Turbine steady flow curves were measured in an extended range, taking intoaccount different waste-gate valve settings (WG = driving shaft rotationangle)

A substantial increase in turbine mass flow rate was observed also in thecase of partial WG openings

In the meanwhile, turbine overall efficiency (’t, referred to the totalavailable gas energy) decreased definitely when opening the by-pass valve

1.00 1.25 1.50 1.75 2.00 2.25 2.50Expansion ratio (total to static)

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

Turb

ine

mas

sflow

rate

fact

or

[kg√

K/s

bar]

1.00 1.25 1.50 1.75 2.00 2.25 2.50Expansion ratio (total to static)

0.10

0.20

0.30

0.40

0.50

0.60

0.70

Turb

ine

o ver

allef

fici

ency

3T

nT

T3

n rpm

T K

20003000400055007000

αWG [deg]

082060

sttot

cTCm

sttot

tTCmTStt

hMP

hMP

'


Mass flow results for different flowconfigurations were expressed in termsof equivalent isentropic flow area Aeq

AeqR turbine rotor (combined flow) AeqWG WG valve (combined flow) A*eqWG WG valve (single flow) Aeq tot rotor + WG (measured) A*eq tot rotor + WG (calculated)

Both turbine rotor and waste-gate swallowing capacity proved to be lower inthe case of combined flow (rotor + by-pass port), probably due to theinteractions between the two flow components which take place within theturbine volute casing

Total mass flow rate calculated starting from turbine rotor and waste-gatesingle flow curves (A*eq tot) resulted substantially higher than measured level(Aeq tot), with differences ranging between 10 and 25 %

0 10 20 30 40 50 60 70Waste-gate opening [deg]

0

1

2

3

4

5

6

7

8

9

10

11

‏Equiv

alen

t is

entr

opic

flo

w a

rea Aeq tot

*

Aeq tot

AeqWG*

AeqWG

AeqR

3

T3 4

n/ T =3000 rpm/ K

p /p =1.2


0

1

2

3

4

5

6

7

8

9

10

11

‏Equiv

alen

t is

entr

opic

flo

w a

rea Aeq tot

*

Aeq tot

AeqWG*

AeqWG

AeqR


0

1

2

3

4

5

6

7

8

9

10

11

‏Equiv

alen

t is

entr

opic

flo

w a

rea


0

1

2

3

4

5

6

7

8

9

10

11

‏Equiv

alen

t is

entr

opic

flo

w a

rea Aeq tot

*

Aeq tot

AeqWG*

AeqWG

AeqR

Aeq tot*

Aeq tot

AeqWG*

AeqWG

AeqR

3

T3 4

n/ T =3000 rpm/ K

p /p =1.2

Analysis of turbine and WG mass flow contributionsAnalysis of turbine and WG mass flow contributions

To allow the by-pass component to be measured (by a hotwire probe), a proper configuration of the turbine outletcircuit was set up, using an exit pipe fitted with a dividingseptum


Turbine overall efficiency can becalculated referring to

the total mass flowing throughthe system (rotor + waste-gate)(’t)

the rotor mass flow rate (’t R)

Effect of WG opening on turbine efficiencyEffect of WG opening on turbine efficiency

TCmsttot

tt

hMP

'

TCmstR

tRt

hMP

' 0 10 20 30 40 50 60 70Waste-gate opening [deg]

0

0.2

0.4

0.6

0.8

1

1.2

Turb

ine

effici

ency

(ref

err e

dto

clos

ed

WG

conditio

n)

'tη't Rη

n/√T3 = 3000 rpm/√K

pT3

/ p4

= 1.2 bar

Efficiency referred to the total mass flow rate (η’t) significantly decreasedwhen opening the waste-gate valve, due to the relative change of thisquantity

A different behaviour was found for the efficiency referred to the rotor massflow rate (η’tR), with a minimum at intermediate waste-gate settings (αWGbetween 20° and 30°), followed by a slight increase for larger openings


ContentsContents

Introduction


Steady flow results


Conclusions


Unsteady flow investigationUnsteady flow investigation

Different turbine exhaust circuit configurations

A Simple mixing pipe B Short septum C Extended septum

Test conditions: constant turbine rotational speed factor: n/√T3 = 4000 rpm/√K

constant mean inlet pressure: p3m = 1.4 bar

different by-pass valve settings: αWG=0, 8, 15, 20, 25, 35, 50 and 60°

pulsating flow generated by rotating valves

two pulsating flow frequency levels (f = 40 and 66.67 Hz), corresponding tolow engine rotational speed values (1200 and 2000 rpm respectively)


Turbine inlet pressure diagramsTurbine inlet pressure diagrams

Pulse frequency confirmed to significantly affect pressure diagrams, resultingin substantial modifications of both pulse shape and amplitude, due to thewave action in pipes

Pressure oscillation profiles, instead, were similar when working at constantpulsating flow frequency

A clear increase in turbine inlet pulse amplitude at wider by-pass openingswas observed as a consequence of the higher total mass flowing through thesystem

α3 W G

3m

n/ T = 4000 rpm/ K = 20°

Configuration A p = 1.4 bar

0 1 2 3 4time/pulse period

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9Pre

ssure

[bar]


1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Pre

ssur e

[bar]

f = 66.67 Hz

f = 40 Hz

3 3mn/ T = 4000 rpm/ K f =40 Hz Configuration A p =1.4 bar


1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Turb

ine

inle

tpre

ssur e

[bar]


1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Turb

ine

inle

tpre

ssure

[bar]


1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Turb

ine

inle

tpre

ssure

[bar ]


1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Turb

i ne

inle

tpre

ssure

[bar]

αWG =0 αWG =8°

αWG =20° αWG =60°


Effect of WG opening on waves propagationEffect of WG opening on waves propagation

Flow at the turbine outletbecame significantlyunsteady for wide waste-gate openings

When using a divided exitpipe (configurations B andC), pulse amplitude at theby-pass exit proved to bemore remarkable formaximum WG settings,highlighting a significanttransmission of flowunsteadiness through thevalve port

The hypothesis ofconstant pressuredownstream of the turbine(often used withinsimulation models)confirmed to beunacceptable, especially inthe case of opened WG

3 3mn/ T =4000 rpm/ K f=40 Hz ConfigurationB p =1.4 bar

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outlet

pre

ssure

[bar]

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outlet

pre

ssure

[bar]

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outlet

pre

ssure

[bar]

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outle t

pre

ssure

[bar]

p4WG

p4RαWG =0 αWG =15°

αWG =35°

αWG =60°

3 3mn/ T =4000 rpm/ K f=40 Hz ConfigurationB p =1.4 bar

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outlet

pre

ssure

[bar]

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outlet

pre

ssure

[bar]

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outlet

pre

ssure

[bar]

0 1 2 3 4

time/pulse period

0.98

1.02

1.06

1.10

1.14

1.18

1.22

Outle t

pre

ssure

[bar]

p4WG

p4R

p4WG

p4RαWG =0 αWG =15°

αWG =35°

αWG =60°


Measured outlet pressure signals (1/2)Measured outlet pressure signals (1/2)

In the case of a simple downstream mixing pipe (configuration A)pressure signals at the waste-gate outlet were affected by higherfrequency disturbances when the by-pass port was opened,probably due to significant interference with the flow from theimpeller


Measured outlet pressure signals (2/2)Measured outlet pressure signals (2/2)

This effect was substantially reduced by using a connecting pipe fittedwith a dividing wall between the two flow components (configuration Band C)


Instantaneous turbine mass flow rateInstantaneous turbine mass flow rate

3 mn/ T =4000rpm/ K f=40Hz =1.33 mn/ T =4000rpm/ K f=40Hz =1.3

An increasing amplitude of massflow rate oscillation was found whenopening the waste-gate valve

A noticeable phase shift wasdetected between measuredpressure and mass flow profiles,due to the filling and emptying ofthe turbine volute casing

This effect was highlighted by anhysteresis loop surrounding thesteady state curve, the magnitudeof which increased in the openedwaste-gate region

1.1 1.2 1.3 1.4 1.5 1.6pressure ratio

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

Mass

flow

para

mete

r[k

g√

K/s

bar]

40 Hz

Steady state

1.1 1.2 1.3 1.4 1.5 1.6pressure ratio

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

Mass

flow

para

met

er[k

g√

K/s

bar

]

40 Hz

Steady state

αWG =0

α °WG =20

1.1 1.2 1.3 1.4 1.5 1.6pressure ratio

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

Mass

flow

para

mete

r[k

g√

K/s

bar]

40 Hz

Steady state

1.1 1.2 1.3 1.4 1.5 1.6pressure ratio

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

Mass

flow

para

met

er[k

g√

K/s

bar

]

40 Hz

Steady state

αWG =0

α °WG =20


ConclusionsConclusions

Turbocharging is becoming a key technology for both gasoline and dieselautomotive engines

Dedicated and fully flexible test facilities are a fundamental tool toinvestigate turbocharger performance

Several aspects related to automotive turbochargers operation requirefurther investigation: definition of TC turbine and compressor steady state characteristics

over the full potential operating range measurement of instantaneous turbine operating parameters in

unsteady flow conditions and comparison with the results providedby simulation models

development of correlation criteria between steady and unsteadyturbine average performance

partial and unequal two-entry turbine operation, including theeffect of out-of-phase pulsating flows

optimization of engine valve control strategies and exhaust circuitgeometry to improve TC transient performance

effect of unsteady flow operation on compressor surge ……


ConclusionsConclusions

The results of an extensive experimental investigation on the behaviorof a turbocharger for downsized SI automotive engines werepresented, focusing on the effect of the waste-gate valve opening onturbine steady and unsteady performance

Different aspects were highlighted by the study:

when opening the waste-gate, the total system mass flow ratecan’t be calculated assuming the turbine and the by-pass valveas two nozzles working in parallel under the same overallexpansion ratio

the definition of turbine efficiency in the region of openedwaste-gate should take into account the fluid portion effectivelyworking through the turbine rotor

in typical automotive applications flow unsteadiness at theturbine outlet becomes significant for wide waste-gate openings

instantaneous mass flow rate is influenced by the filling andemptying phenomena in the turbine volute casing, resulting inhysteresis loops surrounding the steady state curve


UNIGEUNIGE –– ICEG ReferencesICEG References

M. Capobianco, A. Gambarotta, "Unsteady flow performance of turbochargerradial turbine", 4th International Conference on Turbocharging and Turbochargers,Instn Mech Engrs, London, 1990.

M. Capobianco, A. Gambarotta, "Variable geometry and waste-gated automotiveturbochargers: measurements and comparison of turbine performance", ASMETransactions, Journal of Engineering for Gas Turbine and Power, 1992.

M. Capobianco, A. Gambarotta, “Performance of a twin-entry automotiveturbocharger turbine”, ASME Energy-Sources Technology Conference andExhibition, Houston, 1993.

M. Capobianco, S. Marelli., “Transient Performance of Automotive Turbochargers:Test Facility and Preliminary Experimental Analysis”, 7th International Conferenceon Engines for Automobile (ICE 2005), Isola di Capri, Settembre 2005, SAE Paper2005-24-066.

M. Capobianco, S. Marelli, “Turbocharger turbine performance under steady andunsteady flow: test bed analysis and correlation criteria”, 8th InternationalConference on Turbochargers and Turbocharging – I.Mech.E., London, 5/2006.

M. Capobianco, S. Marelli, “Unsteady flow behaviour of the turbocharging circuitin downsized SI Automotive Engine”, paper F2006P119, FISITA 2006 WorldAutomotive Congress, Yokohama, Ottobre 2006.

M. Capobianco, S. Marelli, “Waste-gate turbocharging control in automotive SIengines: effect on steady and unsteady turbine performance”, SAE 14th AsiaPacific Automotive Engineering Conference (APAC-14), August 5-8, 2007,Hollywood, SAE Paper 2007-01-3543

31

Thank you for the attention!

For more information and contact:

www.iceg.unige.it

31Silvia Marelli – University of Genoa – Advanced Charging & Downsizing Concepts – 2nd April 2008

Documents

Waste-Gated Turbochargers Behaviour Under Steady · PDF fileWaste-Gated Turbochargers Behaviour Under Steady and Unsteady Turbine Operation ... 2nd April 2008 12 ... C compressor PC