vehicle demonstrator w/ 2-stage turbo si engine · schernus, wedowski et al. /...

Schernus, Wedowski et al. /

FEV_2stage_SI_demonstrator-GTConf2009.ppt 1

Titel / Autor / Datum

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© by FEV – all rights reserved. Confidential – no passing on to third parties

Vehicle demonstrator w/ 2-stage turbo SI engine – Simulation based layout of the GT² engine

Stefan Wedowski1, Sandra Glück2, Rolf Sauerstein3, Frank Schmitt3,

Markus Westermaier1, David Oh2, Christof Schernus1, Mark Subramaniam4

1 FEV Motorentechnik GmbH, 2 VKA, RWTH Aachen University, 3 BorgWarner Turbo Systems Engineering GmbH,

4 FEV Inc., Auburn Hills

GT-SUITE Conferences 2009Frankfurt/Main – 2009-11-09 Birmingham, MI – 2009-12-07

Results shown in this presentation shall indicate the value of GT-POWER

along with 3D CFD in the creation of new powertrain applications. When we

eventually decided to really build this demonstrator vehicle with a two-stage

turbocharged engine, there were just about 5 ½ months until the date to

exhibit the car on the 18th Aachen Colloquium "Automobile and Engine

Technology“. This period included the summer vacation season, which

usually limits the available human resources required for such a project.

Hence, a strongly motivated crew and efficient virtual engineering tools

such as GT-SUITE were indispensable to cope with this challenge.

At this point I wanted to thank my co-authors at BorgWarner, at the RWTH

Aachen University and at FEV for their support and for giving me the honor

to present the results of the work.




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Content

Motivation and Targets

Concept

Thermodynamic Layout

Package

Model Validation

Conclusions

My presentation will start with the motivation and targets for this project.

Next the engine concept will be outlined. Details of the thermodynamic

layout will be presented, followed by a short insight into the narrow

package, and the rapid prototyping. Model predictions will be displayed

before the presentation ends with brief conclusions.




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Content


Concept


Package

Model Validation

Conclusions




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IntroductionGlobal Warming

Source: http://en.wikipedia.org/wiki/File:Instrumental_Temperature_Record.png

The temperature records of the past 130 years indicate a more or less

continuous rise of temperatures in the past (*) 40 years, which coincided

with increasing energy consumption of industry, households and traffic.




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IntroductionCoincidence with increasing molar fraction of CO2

Source: http://en.wikipedia.org/wiki/File:Mauna_Loa_Carbon_Dioxide-en.svg

Taking a closer look at these last four to five decades, we see also a

continuous increase of the year average carbon dioxide mole fraction in the

atmosphere. It is widely accepted that this increase originates from

combustion of fossil fuels, and that the greenhouse effect caused by

enriching the atmosphere with CO2 and other gaseous emissions like N2O

and CH4 contributes to global warming.




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IntroductionPeak Oil indicates limited resources

Source: http://en.wikipedia.org/wiki/File:Hubbert_world_2004.png

Moreover, the availability of oil is limited. While most of the oil wells in the

USA have already seen their peak oil in the early seventies, other oil

producers have been facing declining oil delivery rates in the following

decades. And there are rumors about Saudi Arabia and other OPEC

countries, that they could not produce more oil in 2008 even though the

crude oil prices were very attractive.




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IntroductionPoliticians react

In view of these scenarios, politicians react, and the European Commission

sets a mandatory average CO2 emission of 120 g/km in NEDC for all new

passenger cars an OEM sells in 2012. Because 10 g/km may be attributed to

fuel-side measures such as bio-fuel blends, new passenger cars shall not

produce more than 130 g/km of CO2 in operation using traditional fuels.

This applies in the same way to conventional motor cars as well as hybrid

powertrain vehicles.

Today, the focus of my presentation is on motor technology and on

downsizing aiming to operate the engine in higher specific loads and hence

better brake efficiency.




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IntroductionDownsizing to save fuel and CO2

Approach:

� Replace a 3.5 ltr V6 by 1.8 ltr downsizing concept

� Obvious challenges:

� Full load performance

� Tip-in

� Drive-away from stand-still

-17%

CO2-NEDC 0-100 km/h 80-120 km/h 6th gear

base 3.5l-V6-NA, VVT FEV GT2

FEV GT2, VCR

-10.5%-2.2%

-23%

To

rqu

e [

Nm

]

150

200

250

300

350

400

Engine Speed [rpm]

1000 2000 3000 4000 5000 6000

3.5l NA 1.8l TC 1.8l 2-stage TC (GT 2)

(SGT)

The idea of downsizing is not new. But recent trends in the market toward

downsizing take a more rigorous approach. E.g. BMW will no longer sell its

new 7 series with a V8 diesel. This engine will be replaced by a 2-stage

turbocharged straight six. [1]

Consequently, other market segments will probably see six cylinder engines

replaced by four cylinders. But it will be difficult to convince a six cylinder

client to step back from his prestigious and smoothly running acquaintance

toward a small straight four. This engine will have to offer him something,

that makes her or him want this prime mover.

Aiming at a 3.5 liter V6, it takes significantly higher targets for the

downsized engine than those for our previous SGT engine, which was a 1.8 l

GDI engine with single turbo and central injector. The targets for this GT²

engine (for Gasoline Twin Turbo) are 26 bar BMEP for most of the speed

range and a specific power output of 120 kW/liter.

With this downsizing engine, the same car shall emit 17% less CO2 in the

European test cycle, and its acceleration from 0-100 km/h as well as from

80-120 km/h in 6th gear shall be improved compared to the V6 car.




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Downsize to 120 kW/ltr

Compressor Air Flow

Co

mp

res

so

r P

.R.

/ -

Low-End

Torque

Ex

h.

Ba

ck

pre

su

re

Rated

Power

Base 90 kW/ltrBase 90 kW/ltr

Downsize to 120 kW/ltr

IntroductionLimits of 1-Stage-Charging

� 90…100 kW/ltr can be realized with 1-stage charging

� add. charging optional for low-end torque improvement

� Pe/VH → 120 kW/ltr ⇒⇒⇒⇒ 2-stage charging required

due to limited compressor range / turbine pressure ratio

This target decision leads to new technical challenges. (*) A single-stage

turbo has enough compressor flow range for a specific power of 90 kW/l

along with pressure ratio for satisfactory low end torque. (*) Also, exhaust

backpressure complies with turbine layouts. Now, the new target of 120

kW/l requires (*) higher boost pressure ratio and a larger compressor flow

range to enable the target low end torque at engine speeds as low as 1500

rpm. In a single stage turbo layout, this may lead to (*) pressure ratios across

the turbine that can be considered (*) critical. The step to a two-stage

turbocharger overcomes these limitations.




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Content


Concept


Package

Model Validation

Conclusions

Now, let me discuss a few turbo concepts for such a high performance.




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„Bi/Twin-Turbo“ 1-Stage Register (Parallel)

Example : BMW 335i

ConceptSystems with 2 T/C

Examples : Porsche 959~ Jaguar Diesel

This slide shows engine systems with two turbochargers, both compressing

the charge air in a single stage. The first system is a bi-turbo layout with

both turbines fed continuously from a set of three cylinders each. Also the

concept on the right hand side employs the turbos in parallel arrangement to

compress the air in a single stage. The one displayed here was used in the

Porsche 959 [2]. A similar solution has been presented by Ford at the

Aachen Colloquium as boosting concept for the new Jaguar V6 Diesel [3].

That Parallel-Sequential Turbocharging uses a VGT turbocharger, which is

assisted by a fixed geometry turbo only at higher engine speeds.




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System specific actuators:

High-Pressure-Turbine bypass

� on/off bypass (active), no control function

� at low speed complete mass flow through

turbine

� from low/mid speed on complete mass flow

bypassed

High-Pressure-Compressor bypass

� on/off bypass (active)

� complete mass flow bypassed

External Bypass (Overall-Bypass)

� conventional function of turbine control but

both turbines simultaneously affected

serial / serial

„FEV2“

HPC-BP HPT-BP

Ext. BP

Example : none

ConceptTwo Stage Turbocharging Architectures

2-stage turbocharging is called like this, because the boost air is compressed

in two sequential stages. This picture displays an interesting concept

suggested by Reiner Wohlberg.

The exhaust gas propels the HPT first before driving the LPT with the

remaining pressure ratio. Boost pressure is controlled at any time using an

external bypass. Because the wastegated mass flow also bypasses the LPT,

the latter contributes less to boosting. Hence, the HP turbine delivers a larger

share of turbo power, and its compressor operates at high specific work and

favorable efficiency in the low speed range. At a certain point the HP

bypasses open, the LP TC speeds up, and the external bypass now controls

the low pressure turbocharger.

The system has advantages in compressor outlet temperature, because the

compressors operate near optimum efficiency. But there are several

challenges related to this system, too:

1) transient control in acceleration: The HP turbo is controlled using the

external bypass. Its gas flow does not propel the LP turbo. When opening

HP turbine bypass at higher full load speeds, the LP turbo starts revving up

from rather low speeds.

2) Additional package space is required for the external bypass.




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System specific actuators:

High-Pressure-Turbine bypass

� Vacuum actuator

� low speeds -> controlled wastegate function

for High Pressure Turbine

� from mid speed on complete mass flow

bypassed toward Low Pressure Turbine

High-Pressure-Compressor bypass

� Vacuum actuator

� on/off bypass (active)

� complete mass flow bypassed

Low-Pressure-Turbine wastegate

� Positive pressure actuator

� conventional function of turbine control

serial / serial

„GT² concept“

HPC-BP HPT-BP

LPT-WG

Example : BMW 123d

ConceptTwo Stage Turbocharging Architectures

Because of the availability of prototype parts and the tight schedule and also

because of the narrow package of the target vehicle, we chose a more

conventional 2-stage turbo architecture for our concept car in the first step.

This system is similar to what is in production in the BMW 123d, but its

application to gasoline engines is quite new.

The system features a controlled bypass for the HPT, a switchable bypass for

the HPC and a large wastegate turbocharger as low pressure stage. While the

HP bypass has a vacuum actuator, default open, the LP wastegate works on

positive pressure, default closed.




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ConceptGT² (Gasoline Twin Turbo) Demonstrator Data

� Serial sequential 2-Stage Turbocharging System

� Turbochargers by BorgWarner Turbo Systems designed for 1,8ltr-I4 SI-Engine:

� Rated Power: 216 kW (120 kW/ltr)

� Max. Torque: 375 Nm @ 1500 rpm

� Fuel Economy Target:

� Fuel consumption -17% or

� Mileage +20%, respectively

vs. 3.5ltr-V6 NA reference engine

Accordingly, our gasoline twin turbo concept demonstrator car features a

serial-sequential 2-stage turbocharger, the turbo machinery of which was

generously provided by BorgWarner Turbo Systems in Kirchheim-

Bolanden. They also helped us finding the appropriate compressor wheels

and trim to match our boost and mass flow requirements for the performance

targets of 120 kW/liter and more than 200 Nm/liter from 1500 to 5500 rpm.

The CO2 footprint of that engine shall be 17% less than a 3.5 liter V6

breathing from atmosphere.




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ConceptGT² Engine and Vehicle Specification

Engine Specification

� Displacement 1.8 mm

� Bore 81 mm

� Stroke 87 mm

� Stroke / Bore 1.074

� Compression Ratio 8.5

� Intake Cam Phaser 60 deg CA

� Exhaust Cam Phaser 60 deg CA

� Peak Firing Pressure up to 140 bar

� Ignition NGK 12 mm

� Central Injector

� Injector Type Bosch HDEV 4

Piezo, outward

opening

� Fuel rail pressure up to 200 bar

Vehicle Specification

� Ford Focus ST Model Year 05

� Production gear box

� Production type intercooler

from high-performance vehicle

� Production type catalyst

Turbocharger Specification

� High-Pressure Stage

� Compressor 1574 CBK

� Turbine KP35-240.82

� Low Pressure Stage

� Compressor 2283 DCBHA

� Turbine K04-6.88

This slide gives you some more details about the engine geometry

parameters, the flexibility in valve timing, and fuel supply. The vehicle for

the GT² concept demonstrator car is a used Ford Focus ST along with other

production parts. A KP35 turbine is used on the high pressure stage, and K04

turbine as low pressure stage.




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ConceptBase Engine Modifications

Steps to upgrade the SGT to the GT² engine:

� Reduction of Compression Ratio from 9.8 to 8.5 by cylinder head gasket to be safe against mega-knock. Stepwise increase planned in future investigations.

� Intake ports with increased tumble

� New casted exhaust manifold

� Integration of BorgWarner-Turbochargers

� Low back pressure exhaust system

� Upsized charge air cooler / intake piping / throttle-body

� Implementation and calibration of knock detection and control (dSPACE)

� 2-stage turbocharger control: function development and calibration (dSPACE)

In order to upgrade the previous SGT engine to the GT² engine, we took two

measures against mega-knock and pre-ignition: To be on the safe side, the

compression ratio was reduced from 9.8 to 8.5, which will be revisited in

future investigations. FEV’s CMD process predicted further advantages in

combustion speed from enhancing tumble, so the intake ports were

modified. The GT-POWER knock model told us these measures were safe.

Luckily, this statement did not become invalidated by experimental work.

Otherwise, we hadn’t had the demonstrator car ready for the Exposition.

For the first proof of concept, we tried to make the engine work without a

larger charge air cooler but without intercooler between the stages.

Eventually, we created a rapid prototype control for knock and boost

pressure based on dSPACE equipment.




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Content


Concept


Package

Model Validation

Conclusions

Next, we get to the thermodynamic layout.




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Thermodynamic Concept Layout Compressor Layout LP-Stage

pre

ss

ure

ra

tio

[-]

1.0

1.5

2.0

2.5

3.0

3.5

4.0

corrected mass flow [kg/s]

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0.60

0.650.68

0.70

0.72

0.74

0.76

0.65

0.68

0.700.72

0.74

0.74

5000076000

102000

122000

139000

152000

162000

172000

185000

166000

166000

51000

78000

105000

126000

143000

157000

Compressor with same wheel diameter

but significantly more flow capacity and

higher boost pressure ratio.

2283DCBHA(Compressor selected

for GT² engine)

2275E(Compressor used

on SGT engine)

Trim (d/D) has been modified

from 75 to 83%

Comparing the compressor maps of the SGT engine in blue to the low

pressure stage of the GT² engine in gray, it is obvious, that the new T/C

delivers higher mass flow rate and higher boost pressure (*) at same speed

lines, although the compressor wheel diameter is equal. Our partners at

BorgWarner exchanged the compressor wheel type “E” having 4 full and 4

split blades by a 6+6 blade “D” type wheel allowing higher boost pressure

ratio. Then, (*) they adjusted the flow capacity by increasing the trim from

75 to 83%.




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Vehicle

Model

T/C

GT-POWER Model of the GT² Engine– Engine model with T/C subassembly

The GT-POWER model is an air-to-air model with limited details of exhaust

mufflers. (*) It features air cleaner, turbocharger, charge air cooler and

several control blocks.

For simulation of vehicle transients, a (*) vehicle model has been linked to

the crank train object of the GT-POWER model.




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LP-TurbineControl HP-Comp.

Control

Pop-offValve

HP-TurbineControl

GT-POWER Model of the GT² Engine– T/C subassembly

LP-TC

HP-TC

The turbo subassembly includes the two turbochargers and the bypasses of

the high pressure stage and the pop-off or diverter valve modeled separately.

Just the wastegate of the LP turbine has been modeled the traditional way for

simplicity.




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GT-POWER Model of the GT² Engine– Model features

Model used first for *prediction* of future engine

� EngSITurb Combustion model

� Model parameters adopted from previous SGT engine model

� Employing STL data of target combustion chamber

� EngKnock Knock Model

� Model parameters adopted from previous SGT engine model

� Wiebe combustion model using parameters evaluated from EngCombSITurbpredictions

� Draft geometry data stepwise updated with packaged geometry from CAD

� Heat transfer and wall temperatures using heat conduction objects in steady-state and transient applications

� Transient vehicle simulations employ full detailed engine model

The modeling approach included the validation of turbulent combustion and

knock models using measured data from the previous engine. For the more

time consuming parameter variations of the system architecture, Wiebe

models were applied using mapped heat release profiles of the turbulent

combustion model.

The design work was supported by stepwise exchange of information and

advice between design and simulation.

Eventually, the transient vehicle simulations employed the full detailed

engine model in order not to miss any effect of pulsating flow on turbo

efficiency, pressure response, heat transfer, etc.




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Concept Layout Modes of Turbo Operation

� LP stage can provide boost for ≥ 2500 rpm with HP

stage bypass fully open

� HP-Stage delivers required boost for full load below

2500 rpm

� Efficiency trade off shifts boundary for single LP stage

operation to higher engine speeds

� Transient control runs HP stage in larger map areas

For high torque at engine speeds of 2500 rpm and higher, just the new

enhanced LP stage would be sufficient, (*) as indicated here in operation

with bypasses of HP compressor and turbine fully open. However, this

would leave the customer with the impression of (*) a very weak starting

torque and also result in poor drivability. Therefore, the small T/C in the HP

loop is required to (*) fill the gap for the lower speeds.




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“NA” Operation (3)

4

1

32





2500 rpm




Mode HPT-BP HPC-BP LPT-WG

1 closed closed closed

2 control closed closed

3 open open closed

4 open open control

Stationary Operation

The stationary operation map of the engine can be divided into the following

areas: In the lower part load, so-called naturally aspirated operation, the

wastegate of the low pressure stage is closed in lack of positive pressure for

its actuator. Increasing load involves boost pressure control by firstly

opening the LP wastegate and gradually closing it again towards higher load.

For speeds below 2500 rpm there exists a boundary curve (3), where the LP

wastegate is closed, and the HP stage bypasses are just still open. Exceeding

this curve will close the HP compressor bypass and employ the vacuum

actuator for the HP turbine bypass to increase the boost pressure in area 2,

until also the HP turbine bypass is fully closed for full load speeds below

1500 rpm, which is indicated as mode 1.




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2500 rpm




Mode HPT-BP HPC-BP LPT-WG

1 closed closed closed

2 control closed closed

3 open open closed

4 open open control

Transient Operation

LP-Stage Only

Operation (4)2-Stage Charging

Operation (2)

“NA” Operation (3)

1

When the engine operates transient, the area of 2-Stage charging is much

larger, because the HP-TC speeds up much faster and responds better than

the LP-TC. While the present calibration was focused to make the car

drivable until the Colloquium, future work will explore the limits of the

transient 2-stage operation in more depth.




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with operating HP-Stage

-> overall Airflow -> LP-TC speed rises

-> LP-stage pressure ratio at low speeds increased by HP-Stage

Concept Layout

Comparison 2-stage to 1-Stage

The presence of the HPC increases mass flow at low engine speeds.

Therefore, also the LPT speeds up and delivers higher boost pressure below

1700 rpm than if operating alone.




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Content


Concept


Package

Model Validation

Conclusions

Now come a few pictures how the turbocharger was integrated with the

engine.




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PackageGT² Assembly 2009-09-25

This is the front view on the engine. Slight modifications were done to the

design when building the prototype by further reducing the distance between

turbine outlet pipe and generator for the sake of a smoother bend.




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PackageGT² Assembly 2009-09-25

The view from the right side shows the exhaust downpipe well aligned with

the engine envelope.




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PackageGT² Vehicle Setup 2009-09-25

Admittedly, the engine compartment is very narrow for such an application.

The insulations between hot parts and parts to be protected will look

different in a production vehicle, and the clearances would be larger, too.




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PackageGT² Vehicle Setup 2009-09-25

Nevertheless, the car ran smoothly during vehicle calibration; and its

performance was appreciated on many test drives during the Aachen

Colloquium one month ago. When dismantling the engine thereafter, no

damages or wear were observed. The car was reassembled and is available

for test drives to interested clients in Aachen until further notice.




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Content


Concept


Package

Model Validation

Conclusions

Since the GT-POWER model was used as a predictive tool for the layout of

an engine, measurement data of the target engine became available only

after the required simulations were done. Therefore, the validity of the

model could only be checked a posteriori.




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Model Validation Transient Simulation Results and Measurement

3rd Gear, Full-Load-Acceleration from 25 km/h

As expected, not every experimental result looked like its model prediction.

By taking into account feedback signals from sensors and actuators in the

car, the model was then used to understand, what caused the differences.

This simulation of a tip-in from 25 km/h takes into account measured bypass

flap positions and feeds them into the model. We found, that unintentionally

the flaps were not fully closed, which resulted from exhaust backpressure

and still to be improved closing forces of actuators. The torque rise after tip-

in and the acceleration of the vehicle are affected by this behavior and are

expected significantly better after the holding forces will be adjusted.

But nevertheless imposing the flap positions in the model leads to a good

match of the TC-Speeds.




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Model ValidationTransient Simulation Results and Measurement

3rd Gear, Full-Load-Acceleration from 25 km/h

The calculated boost pressure build-up also nearly fits to the measurement

data, so that the GT-POWER/GT-Drive Model seems to predict the behavior

of the engine and vehicle in an appropriate way.




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Pre

ssu

re R

ati

o [

-]

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Corrected Mass Flow Rate [kg/s]

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0.760.74

0.720.70

0.68

0.66

0.64

0.60

0.55

49600

76000

102000

122000

139000

152000

162000

172000

185000

Pre

ssu

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ati

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-]

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Corrected Mass Flow Rate [kg/s]

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0.74

0.72

0.68

0.66

0.64

0.62

0.60

0.55

0.70

77400

119000

160000

191000

217000

237000

268000

253000

HP-Stage

Operating

Point

LP-Stage

Operating

Point

Overall

Operating

Point

HP-Stage Compressor

Map (1574CBK)

LP-Stage

Compressor Map

(2283DCBHA)

Model ValidationProgress of Turbocharger Operating Points (Stationary)

Looking at the steady state operation points in all compressor (*) maps, we

plot the points of the (*) high pressure stage in red, the low pressure stage

(*) in blue, and the overall result of both stages (*) in green.

The (*) diagram shows that the HP stage fades out after reaching the target

torque and the low pressure stage takes over. After the HP stage bypass is

completely open, the total pressure ratio is equal to the one of the low

pressure stage.

The picture shows, that the coordination of both compressor stages can be

improved to make them work at better efficiencies in 2-stage operation.

Possible measures include revised bypass control of both turbines and/or

resized high-pressure turbine and compressor.




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Vehicle demonstrator w/ GT² engine

Conclusion

� Feasibility of 2-stage turbo GDI downsizing engine

concept with 208 Nm/l and 120 kW/l demonstrated

� Further research and optimization work planned

� Concept layout elaborated with GT-SUITE

� Simulations allowed to cope with tight schedule

To conclude my presentation, we can say the feasibility of a gasoline engine

with two stage turbocharging has been demonstrated, although a lot of

improvement work is yet to be done.

The concept has been evaluated using GT-POWER, and the simulations

were indispensible to create this demonstrator car in the very narrow

schedule.




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The authors wish to acknowledge further valuable

contributions to the presented work fromDr. Ralf Christmann @ BorgWarner Turbo Systems

Martin Nijs, Tolga Uhlmann &

Stephan Schnorpfeil @ VKA

Reiner Wohlberg, Georg Lütkemeyer &

Carsten Dieterich, Andreas Sehr @ FEV

References:

[1] The 1st Diesel Engine with 2-stage Turbocharging and Variable Turbine

Geometry in Passenger Cars; P. Nefischer, W. Hall, J. Honeder, T.

Steinmayr, P. Langen; 18th Aachen Colloquium "Automobile and Engine

Technology“, 5th - 7th October 2009

[2] Wikipedia contributors, "Porsche 959," Wikipedia, The Free

Encyclopedia,

http://en.wikipedia.org/w/index.php?title=Porsche_959&oldid=326563451

(accessed December 4, 2009).

[3] Parallel Sequential Boosting of the V6 Diesel Engine; L. Bartsch, V.

Smiljanovski, G. Chen, S. Johnson, A. Lilley; 18th Aachen Colloquium

"Automobile and Engine Technology“, 5th - 7th October 2009

vehicle demonstrator w/ 2-stage turbo si engine · schernus, wedowski et al. /...

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