the potential of dual stage turbocharging and miller cycle ... · gt-suite users international...

GT-Suite Users International ConferenceFrankfurt a.M., October 4th 2004

THE POTENTIAL OF DUAL STAGE TURBOCHARGING

AND MILLER CYCLE FOR HD DIESEL ENGINES

F. MILLO, F. MALLAMO, A. CAFARI (Politecnico di Torino)

G. GANIO MEGO (IVECO S.p.A)

Presentation overview

• Introduction

• Experimental set-up

• The engine model

• Engine model validation

• Use of the simulation for the analysis of

possible performance enhancements

• Conclusions

• Introduction




• Use of thesimulation for theanalysis of possibleperformance enhancements

• Conclusions

INTRODUCTION

The search for further enhancements of the specific power output of Heavy Duty Diesel engines has encouraged several manufactures to exploit possible ways to increase the boost level while maintaining peak firing pressure as well as pollutant emissions within acceptable limits.

• Introduction





• Conclusions

INTRODUCTION

While dual stage turbocharging provides indeed a suitable method to achieve a significant increase of the boost level (as well as a wider operating range, due to its higher flexibility), it may nevertheless lead, due to the extremely high values of the combustion pressure, to unbearable loadings on some engine components, as well as to an unacceptable increase of NOx emissions.

Therefore, the increase in the boost pressure that can be achieved by means of dual stage turbocharging, should usually be coupled with measures aiming to maintaining the peak firing pressure within acceptable levels, such as, for instance, reductions of the engine compression ratio and/or of the injection advance.

However, these countermeasures may lead to significant penalties as far as fuel specific consumption and soot emissions are concerned, requiring a careful pro vs. cons analysis, in order to find out a proper trade-off.

• Introduction





• Conclusions

INTRODUCTIONOn the other hand, if the increase in boost level is carried

out in combination with an Early Intake Valve Closure, followed by an in-cylinder expansion of the charge during the last portion of the intake stroke (Miller cycle), significant reductions in peak firing pressure and temperature can be achieved, thus diminishing both pressure and thermal loadings on engine components, as well as NOx emissions, which are extremely sensitive to the combustion temperatures.

Standard Miller

• Introduction





• Conclusions

INTRODUCTION

Standard Miller

For instance, if the air temperature at engine intake can be assumed to be independent from the boost pressure, and if the boost level in the Miller cycle is increased so to reach the same in-cylinder pressure at the beginning of the compression stroke of a "standard" turbocharged engine, equal end-of-compression pressure levels will be attained in both engines, but with lower temperatures in the Miller cycle, as well as with an increased trapped mass of air, which will allow, at constant air/fuel ratio, an increase of the injected fuel quantity and therefore of the engine power output.

• Introduction





• Conclusions

INTRODUCTIONAlthough the Miller cycle concept is well known from the

1950s, and has found several applications for different types ofengines with the main target of increasing the power output while maintaining within acceptable limits mechanical and thermal loadings, the potential for remarkable reductions of NOx emissions has strongly renewed the interest in this technique in the last decade.

However, even if the simulation tool plays a fundamental role for the evaluation of the potential of the Miller cycle, its advantages can only be assessed through a complete and detailed engine model, since several interacting effects have tobe taken into account, such as, for instance:

- effects on the gas exchange process, due to the higher engine backpressure which is needed to operate the turbocharger at higher boost levels;

- effects of boost level enhancement and of the correlated actions (reductions of the injection advance and/or the engine compression ratio) on the combustion process and on the pollutant formation in particular.

• Introduction





• Conclusions

INTRODUCTION

Therefore GT-POWER (with the EngCylCombDIJet model

activated for the analsyis of the combustion process) was

applied to evaluate the potential of dual stage turbocharging

and Miller Cycle for a 6 cylinders in line, 13 litres displacement,

HD diesel engine (IVECO CURSOR 13).

• Introduction





• Conclusions

EXPERIMENTAL SET-UP

MAIN ENGINE FEATURES

397 kW at 1900 rpmMaximum Power

4 valves/cylinderValves

Direct injection with Unit Pump Injectors

Fuel Metering System

Single Stage Turbocharger with Variable Geometry Turbine (VGT) and Aftercooler

Air Intake System

2356 Nm at 1000 rpmMaximum Torque

17 : 1Compression Ratio

12,8 dm3Displacement

135 / 150 mmBore/Stroke

Diesel, 4 stroke6 cylinders in line

Type

• boost level 3 bar

• bmep 23 bar

• spec. output 31 KW / dm3

IVECO CURSOR 13

Several different applications (e.g. trucks, gensets, marine etc.).

• Introduction





• Conclusions

EXPERIMENTAL SET-UP

Temp. meas.

Temp. meas.

Pressure meas.

While the experimental activity and the baseline model validation were carried out on the HD truck engine, the analysis of the dual stage turbocharging and Miller cycle were carried out for a genset engine, at constant revolution speed (1500 rpm) and full load operating conditions.

Experimental investigations were carried out under full loadoperating conditions over a speed range from 800 up to 2200 rpm, recording in-cylinder and fuel injection pressure traces were recorded, along with injector needle lifts.

• Introduction





• Conclusions

THE ENGINE MODEL

AFTERCOOLER

INTAKE

MANIFOLD

EXHAUST

MANIFOLD

TURBOCHARGER

In the baseline model heat release profiles obtained by the analysis of experimental in-cylinder pressure traces were used

• Introduction





• Conclusions

BASELINE ENGINE MODEL VALIDATION

0

500

1000

1500

2000

2500

700 900 1100 1300 1500 1700 1900 2100 2300Engine speed [rpm]

Air

Mas

s Fl

ow [k

g/h]

EXPSIM

AIR MASS FLOW

• Introduction





• Conclusions


TURBOCHARGER SPEED

60

70

80

90

100

110

700 900 1100 1300 1500 1700 1900 2100 2300Engine speed [rpm]

Turb

o Sp

eed

[Krp

m]

EXPSIM

• Introduction





• Conclusions


BOOST PRESSURE

1.8

2

2.2

2.4

2.6

2.8

3

3.2

700 900 1100 1300 1500 1700 1900 2100 2300Engine speed [rpm]

Boo

st P

ress

ure

[bar

]

EXPSIM

• Introduction





• Conclusions


10

12

14

16

18

20

22

24

700 900 1100 1300 1500 1700 1900 2100 2300Engine speed [rpm]

BM

EP [b

ar] EXP

SIM

BMEP

• Introduction





• Conclusions

ENGINE MODEL VALIDATION

The baseline engine model could be used to obtain a first estimate of the enhancement of engine performance that can be attained by means of dual stage turbocharging, for instance by increasing the injected fuel quantity while maintaining the same Air/Fuel ratio of the reference single-stage turbocharged engine.

However, in order to allow a reliable prediction of the effects of boost level enhancement and of the correlated actions (reductions of the injection advance and/or the engine compression ratio) on the combustion process and on the pollutant formation, a refinement of the baseline model was carried out, by means of the multi-zone combustion model for NOx and PM prediction, provided by the EngCylCombDIJet feature.

• Introduction





• Conclusions

REFINED ENGINE MODEL VALIDATION

NOx EMISSIONS AND PEAK FIRING PRESSURES

0

500

1000

1500

2000

2500

3000

700 900 1100 1300 1500 1700 1900 2100 2300Engine speed [rpm]

NO

x [g

/h]

100

125

150

175

200

225

250

Peak

pre

ssur

e [b

ar]

NOx EXPNOx SIMPeak pressure SIMPeak pressure EXP

• Introduction





• Conclusions


SOOT EMISSIONS

0

10

20

30

40

50

60

70

700 900 1100 1300 1500 1700 1900 2100 2300Engine speed [rpm]

Soot

[g/h

]

Soot EXPSoot SIM

• Introduction





• Conclusions


NOX - SOOT EMISSIONS(CONSTANT SPEED 1570 RPM, VARIABLE LOAD)

0

500

1000

1500

2000

2500

20 25 30 35 40 45A / F [-]

NO

x [g

/h]

0

10

20

30

40

50

Soot

[g/h

]

NOx EXPNOx SIMSoot EXPSoot SIM

• Introduction





• Conclusions

ANALYSIS OF POSSIBLE PERFORMANCE ENHANCEMENTS

WASTE GATE VALVE

Low pressure Turbocharger

High pressure Turbocharger

Aftercooler

• Analysis carried out for a genset engine, at constant revolution speed (1500 rpm) and full load operating conditions

• Intercooler between the LP and HP turbocharger stages discarded, mainly because the corresponding higher pressure losses in the circuit were not compensated by remarkable savings in the compression work of the HP stage

• Boost level controlled bymeans of a waste-gate valve on the HP turbine: for genset application, HP turbine characteristics redesigned

DUAL STAGE TURBOCHARGING

• Introduction





• Conclusions


WASTE GATE VALVE

Low pressure Turbocharger

High pressure Turbocharger

Aftercooler

Injected fuel quantity limitedtrying to fulfil the following requirements:

•peak firing pressures below 180 bar, aiming to a target levelequal to or lower than 160 bar(possibly without injection timing retards, to avoid detrimental effects on bsfc), to maintain the same stress levels as in the "reference" single stage turbocharged engine.

• A/F ratio values equal to or higher than those of the "reference" single stage turbocharged engine, so to avoid penalties in soot emissions.




73.9 77.2 77.273.9 73.5

0102030405060708090

100

Reference CR 16 CR 17 CR 16 + HPturbine opt.

CR 17 + HPturbine opt.

[kg/

h]

BMEP FUEL FLOW

BOOST PRESSURE PEAK PRESSURE

05

101520253035



[bar

]

23.4 24.522.8

24.323.5

2.93.2 3.0

3.43.5

0.00.51.01.52.02.53.03.54.04.55.0



[bar

]

158 157 164180171

0

50

100

150

200

250

300



[bar

]


DUAL STAGE TURBOCHARGINGA/F

23.4 23.9 23.0

27.6 27.1

05

10152025303540



[-]

BSFC

200.9 198.3 196.9197.0 195.8

0

50

100

150

200

250

300



[g/k

Wh]

Specific SOOT Emissions

0.0430.035

0.044

0.017 0.019

0.000.010.020.030.040.050.060.070.080.090.10



[g/k

Wh]

Specific NOX Emissions

5.35.9 6.05.8 5.8

0123456789

10



[g/k

Wh]


DUAL STAGE TURBOCHARGING + HP TURBINE OPT.

0

10

20

30

40

50

60BMEP [bar]

P max [MPa]

BSFC/10 [g/kwh]

A/F [-]

Spec.NOx*10 [g/kwh]

Spec.SOOT*1000 [g/kwh]

Reference

CR 17

CR 16

+ 5,5% CR16

+ 6,2 % CR17

- 1,2% CR16

- 2 % CR17

157 CR16

164 CR17

+ 11% CR16

+13 % CR17

- 18% CR16

+ 2 % CR17

• Introduction





• Conclusions


DUAL STAGE TURBOCHARGING +

MILLER CYCLE


DUAL STAGE TURBOCHARGING + MILLER CYCLEBMEP

22.8 23.4 23.5 24.3 24.524.3 24.1

0.0 0.0 0.00

5

10

15

20

25

30

35



[bar

]

FUEL FLOW

PEAK PRESSURE

158 157 164180

171160160

0

50

100

150

200

250

300



[bar

]Miller Supercharging

73.9 77.2 77.273.9 73.576.6 75.4

0102030405060708090

100



[kg/

h]

Miller Supercharging

BOOST PRESSURE

2.93.2 3.0

3.53.43.5 3.6

0.0

1.0

2.0

3.0

4.0

5.0



[bar

]



DUAL STAGE TURBOCHARGING + MILLER CYCLEA/F

23.4 23.9 23.0

27.6 27.125.6 24.0

05

10152025303540



[-]


BSFC

200.9 198.3 196.9195.8197 196.6 195.3

0

50

100

150

200

250

300



[g/K

wh]


Specific NOX Emissions

5.35.9 6.0

5.0 4.7

5.85.8

0123456789

10



[g/K

wh]


Specific SOOT Emissions

0.0430.035

0.044

0.0190.017

0.0350.025

0.000.010.020.030.040.050.060.070.080.090.10



[g/K

wh]



DUAL STAGE TURBOCHARGING + MILLER CYCLE

0

10

20

30

40

50

60BMEP [bar]

P max [MPa]

BSFC/10 [g/kwh]

A/F [-]

Spec.NOx*10 [g/kwh]

Spec.SOOT*1000 [g/kwh]

Reference

CR 17

CR 16

+ 5,5% CR16

+ 4,7 % CR17

- 2,1% CR16

- 2,7 % CR17

160 CR16

160 CR17

- 6 % CR16

-11% CR17

- 41% CR16

- 18 % CR17

• Introduction





• Conclusions

CONCLUSIONS

The potential of dual stage turbocharging and Miller Cycle for a 6 cylinders in line, 13 litres displacement, HD diesel engine was analysed, by means of a 1-D engine simulation fluid dynamic code, coupled with a multi-zone combustion model for NOx and PM prediction.

After a detailed validation process, based on an extensive experimental data set, the engine model was then used to predict the effects on engine performance and emission characteristics of different combinations of dual stage turbochargers, engine compression ratio values and intake valve lift profiles.

The potential for an appreciable increase (about 5%) in the engine power, with a slight decrease in the specific fuel consumption (about 2%) and a remarkable decrease of NOxspecific emissions (up to 10%) was demonstrated.

Acknowledgments

The authors wish to thank Dr. Jean-Louis Jolissaint

(IVECOMotorenforschung) for kindly providing most of the experimental

data which were used for the model validation, and prof. Carlo Ferraro

(Politecnico di Torino) and Dr. Sten Isaksson (Wartsila) for their

valuable suggestions concerning the simulation of the Miller cycle.

GT-Suite Users International ConferenceFrankfurt a.M., October 4th 2004

THE POTENTIAL OF DUAL STAGE TURBOCHARGING

AND MILLER CYCLE FOR HD DIESEL ENGINES

F. MILLO, F. MALLAMO, A. CAFARI (Politecnico di Torino)

G. GANIO MEGO (IVECO S.p.A)

the potential of dual stage turbocharging and miller cycle ... · gt-suite users international...

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