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european gt-suite users’conferencemercure hotel frankfurt airport - october 9th 2006

Optimisation of Gomecsys variable compression ratio enginewith GT-Power simulation tools

George Corfield, Kean Harrison.Prodrive Automotive Technology,Warwickshire, England.

Thank you for the introduction.Good afternoon Ladies and Gentlemen.

“Optimisation of Gomecsys variable compression ratio engine with GT-Power simulation tools”

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•Introduction –Topics covered

•Concept Design

•Simulation Techniques

•Results/Findings

•Summary

contents

Contents

In this presentation I will focus on the design/development techniques used on the GomecsysVariable Compression Ratio engine (VCR); a VCR design which is the intellectual property of BertDe Gooijer at Gomecsys. This project is co-developed by Prodrive Automotive Technology andeligible for funding under the Eureka development scheme.

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introduction

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ACEA CO2 Emmisions Targets

2008,140 g/Km

2012,120 g/Km

2005,163 g/Km

2002,165 g/Km

1995,186 g/Km

100

150

200

1990 1995 2000 2005 2010 2015

Year

CO2

[g/K

m]

TargetCurrent EmmisionsTrend

Introduction

Increasing Worldwide Pressure over the last 15 years from the Kyoto protocol has forced theEuropean Automobile Manufacturers’Association (ACEA) to set increasingly demanding CO2emission targets. This, coupled with individual Government legislation to reduce vehicle basedCO2 emissions, has forced automotive manufacturers to develop new technologies to improvefleet average fuel economy and thus reduce CO2 emissions.

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introduction

Current solutions Diesel

Hybrid

Gasoline

Fuel Cell

Market Drivers NVH

Tax

Familiarity

Cost of Ownership

•ACEA targets can not be meet by Diesel vehicles alone

•Individual targets within the fleet averages

•Hybrid and fuel cell development is slow

•Spark ignition engines have to develop to fulfil the CO2 targets Date to beremoved

Date to beremoved

Introduction

Diesel development is becoming increasingly expensive and can’t meet the emissions targetsalone and, since development in hybrids/fuel cells is slow to take market control, spark ignitionengines have to improve to meet stricter CO2 targets. However, in order to meet the highpower density required by consumers, who are reluctant to pay more for fuel saving deviceswithout performance gains, pressure charging and down-sizing is required. VCR is already atheoretically proven technology and with the distinct advantages of the Gomecsys Atkinsondesign, considerable emission improvements and fuel savings can be made.

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overall concept

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•Based on a 6mm eccentric on thecrankshaft pin

•Electronically actuated compression ratiochange from 6:1 to 15:1

•Complete 720°, 25% over expandedAtkinson cycle.

•30% reduced fuel consumption/CO2 outputwithout sacrificing full load power.

Fuel Conversion Efficiency

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 4 8 12 16 20 24 28

Compression Ratio

Con

vers

ion

Effi

cien

cy

Introduction –Design and concept

Prodrive believes that the prototype 4 cylinder Gomecsys engine will need to produce 100kWfrom 1.1L capacity to have a competitive role in the market place. VCR strategy allows balancebetween full load detonation control and part load thermal/fuel conversion efficiency. Thevariable compression ratio, over-expanded cycle, combined with pressure charging will meet theprogram targets of 30% fuel reduction over the European Union Drive Cycle compared to asimilar engine with the same power output.

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concept design

Date to beremoved

Date to beremovedInternal Ring

GearEccentric

Effects of Worm Wheel angle on piston position

130

140

150

160

170

180

190

200

210

220

0 90 180 270 360 450 540 630 720

Crank Angle (Deg)

Pist

on

posi

tio

nfr

om

cran

ksha

ftce

ntre

(mm

)

0°

10°

20°

30°

40°

50°

60°

Combustion Stroke Exhaust Stroke Intake Stro ke Compression Stro ke

Over expandedpower strokedue to low

BDC

Low gas exchange increasesinternal EGR and elimates valve

pockets

AdvancedBDC with

Retarded BDCwith high

compression

Retarded TDC withlow compression

Design Concept –Detailed design and control

The Gomecsys design combines the VCR technology with several otherunique advantages including:• Compression ratio change from 6:1 to 15:1.• 25% over expansion extracts more energy from each

combustion event and reduces exhausttemperatures and therefore the need to over-fuel for exhaust protection.

• True Atkinson 720 e̊ngine cycle can be optimised to suitengine road conditions

• Reduced piston friction due to low connecting rod angularity (overall frictionneutral q.v. M271 baseline).

• Low TDC gas exchange allows internal EGR at low loads.• Optimised combustion chamber design with no valve cut-outs

necessary whilst maintaining 15:1 CR (low TDC for gasexchange).

• Compatible with existing engine packaging/vehicleintegration.

The reason why we decided to use 1D simulation so early in the project stage was toconfirm the cycle performance before the design competition of complex hardware. Thisalso reduced the time and cost of expensive design iterations. Secondly there was no realavailable ECU strategy for Atkinson/VCR cycle existed so a sound understanding was vital.

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base engine

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Mercedes M271

•Combustion system designed for similarairflow and power output

•Supercharger installation with activecontrol

•Extensive inlet system NVH development•Balance shaft installation•Dual cam phasing

•Build and correlate Mercedes M271 model using our combustion data base.•Update the correlation with test bed/real combustion data.•Modify the standard model with VCR “additions”•Correlate VCR piston motion with known curves and data from similar pressure

charged engines.•Target compression ratio optimisation using end of compression temperature.•Revisited simulation once VCR is running for final sign-off.

Simulation Plan

Base Engine

The Mercedes M271 was chosen for as the base/benchmark engine as it’s the leading marketexample of a lightly downsized pressure charged engine. The M271, which forms the basis forour simulation model, was initially calibrated against generic performance data.Later in the project phase, once the M271 was running with our in-house DP200 Micro Proteuscontrolled ECU, real test bed data was used to correlate the simulation model. The VCRadditions were overlaid to form a high confidence model which was used to increase ourknowledge of trends/interactions and to help in the development of the engine controlstrategy.

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simulation m271 model

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Simulation M271 Model

The validated Mercedes engine model was used in conjunction with PID controllers to form abase line to which the VCR engine would be compared.

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validation m271 model

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0

100

200

300

400

500

BSFC

[g/K

w-h

]

M271 SimulatedData Error

BSFC

5.76%

0200400600800

1000

Tem

pera

ture

(K)

M271 SimulatedData

Error

Exhaust Gas Temperature

2.37%

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10

20

30

40

Pres

sure

[Bar

]

Dyno Data Simulated Data Error

EBP

0.21%

0

0.1

0.2

0.3

0.4

Effic

ienc

y[%

]

M271 Simulated Data Error

Volumetric Efficiency

0.87%

0

2.5

5

7.5

10

Pow

er[K

w]

M271 Simulated Data Error

Engine Power

0.53%

Validation M271 Model

A close correlation was achieved with test bed burn rate data, as can be seen above in thecylinder pressure data. General surface finishes and heat transfer coefficients from our bank ofdata were proved accurate.

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simulation vcr model

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Simulation M271 Model

This slide shows the VCR model which was based on the test bed validated simulation with thepiston control function and post processing channels overlaid, marked in red. This gave us ahigh level of confidence with the simulation and a direct comparison between the two enginedesigns. Day to day target and optimisation work was conducted with the use of PIDcontrollers, a vital labour saving device.

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piston motion

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Where:

Crank shaft angle X Ring gear angle ZCrank Throw A Eccentric offset BCon-rod length C Piston pin height D

Simulation –Challenges

In order to simulate the complex piston motion, whilst maintaining simulationflexibility/simplicity, a control function that related piston motion to ring gear position wasused. This function over-rides the “normal”piston motion and uses the “Nominal PistonStroke”to ground the equation. The result of using the maths function instead of lookuptables was that the compression ratio could be changed by only altering one value in the CaseSetup box, enabling C.R to be varied in the target optimser.

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post processing

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Piston stroke and TDC clearances

-90.00

-80.00

-70.00

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

Dis

tanc

e[m

m]

Com

pres

sion

Com

bust

ion

Exha

ust

Inta

ke

Inta

ke

Com

pres

sion

Com

bust

ion

Exh

aust

Inta

ke

Com

pres

sion

Com

bust

ion

Exha

ust

C.R = 15:1C.R. =10.5:1C.R. = 6:1

Simulation - Post Processing

The standard GT-Power output data is derived from the nominal stroke value set in the model.Since our piston stroke is compression ratio dependent the values are fundamentally flawed.Thus all engine performance data which are stroke dependent [such as BMEP and Volumetricefficiency] have to be post-processed in the RLTcreator. A maths function simply referencesthe Case Setup to find ring gear position and references the correct stroke from look-up tables.The approach of look-up tables was considered prudent to avoid the complex mathematicsinvolved with specifying stroke lengths. The lower diagram shows the full range of TDCpositions and stroke lengths against compression ratio.

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engine sites

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Chassis dynomometer operating cycle and extra-urban cycle

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40

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80

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0 60 120 180 240 300 360 420 480 540 600

Time [sec]

Vehi

cle

spee

d[K

m/h

]

Mid urban

Top urban

Top extra urban

Key Engine Sites:

Mid Urban (32km/h 2nd gear)Top urban (50km/h 3rd gear)Top extra urban (120km/h 5th gear)Maximum Torque (4500rev/min)Maximum Power (5500rev/min)

Engine Sites

Due to a limited time/budget (only a year to deliver and test the prototype engine), several keyengine sites which represented real world driving conditions were looked at. This enabled us toexplore capabilities ahead of VCR engine completion and put VCR technology within context ofreal engine running conditions (Exhaust temperature limits, cylinder pressure limits, end ofcompression temp limits etc). We could then enter the dyno test phase with greater insight andunderstanding of the engine trends and interactions.

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real world benefits –part throttle

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Direct comparison between simulationat 9.55kW with bespoke strategycontrolled with DP200

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100

200

300

400

500

BSFC

[g/k

W-h

]

M271 GomecsysVCR

Reduction

BSFC Reduction

25.6%

0

200

400

600

800

1000

Tem

pera

ture

[K]

M271 GomecsysVCR

Reduction

Exhaust Gas Temperature

7.41%

Real World Benefits

The benefit of increasing fuel conversion efficiency at part throttle is shown in this slide. Forexample when running at 14:1 instead of 9.3:1(at 2500rpm producing 9.55kW) the followingbenefits are shown.Currently, concessions have been made by using the basic combustion model and not exploringthe effects of EGR and VVT between the two engines. One can only conclude increasedsimulation accuracy and ultimate performance output can be achieved.

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real world benefits - wot

900

1000

1100

1200

Tem

pera

ture

[K]

WOT Exhaust Temperatures

Mercedes WOT VCR WOT3000 4000 5000 5500

5%reduction

7%reduction

12%reduction

18%reduction

10

15

20

25

30

35

40

Brak

eEf

ficie

ncy

[%]

WOT Brake Efficiency

Mercedes WOT VCR WOT3000 4000 5000 5500

25%increase

20%increase

9%increase

3%increase

200

300

400

BSFC

[g/k

W-h

]

WOT BSFC

Mercedes WOT VCR WOT3000 4000 5000 5500

30%reduction

24%reduction

10%reduction

3%reduction

Direct comparison between simulationat WOT with bespoke strategycontrolled with DP200

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12.5

15

AFR

Air Fuel Ratio

Mercedes WOT VCR WOT3000 4000 5000 5500

Real World Benefit

Since detonation is typically time consuming to model, a more practical approach was taken:test bed measured end of compression temperatures at Border Line Detonation (BLD) sitesprovided good indication of the cycle’s propensity to knock. This simple approach gave usconfidence that these load sites were close to BLD without the uncertainty of labour intensivecomplex combustion models.The over-expanded cycle lowers exhaust temperatures so fuel enrichment to protect theexhaust at higher loads can be reduced (i.e. move back toward LBT fuelling) until similarhardware limited temperatures as the M271 engine are achieved.

So now we have seen the benefits is summary……

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summary/conclusion:

•Demonstrated our ability to deliver high performance engine programswithin tight dead lines.

•Increased confidence with investment.

•Allowed us to predict advantages of Gomecsysengine with a much reduced investment in time and money.

•Ultimately enabling quicker delivery of a more optimised VCR Atkinson cycleto vehicle demonstrator stage.

Future Development

•Continue VCR test bed development to confirm target performances.

•Develop VCR strategy to vehicle demonstrator level.

Summary/Conclusion

The strategy of using sound practical engine experience in hand with 1D simulation toolsdemonstrates our ability to deliver high performance engine programs to tight deadlines. Alongwith increased confidence in meeting performance targets and small budgets, the use of GT-Power was an extremely valuable tool.

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Thank you for your time.