Simulation of a COMPREX ® Pressure Exchanger GT-Suite Users Conference 2003 Luděk Pohořelský, Jan Macek, Miloš Polášek, Oldřich Vítek Josef Božek Research.

Simulation of a COMPREX® Pressure Exchanger

GT-Suite Users Conference 2003

Luděk Pohořelský, Jan Macek, Miloš Polášek, Oldřich Vítek

Josef Božek Research Center, Czech Technical University in Prague

• Introdution

• 1-D Model of a COMPREX® in GT Power

• Achieved results and model validation

• Detailed analysis of flow and wave phenomena inside

pressure exchanger

• Conclusions

Simulation of a COMPREX® Pressure Exchanger

Presentation Structure

Aims of this Study

• simulation and optimalization of a COMPREX® pressure exchanger in steady operation

• to find tools for optimized-control of pressure exchanger

Ways

• to adapt a general engine CFD tool for this special task

• to validate the model by simulation of a standard COMPREX® pressure exchanger of well-know features

Working Principle of the Standard Pressure Exchanger and its Layout

Alternative boosting device proposed by Brown Boveri & Cie and ETH Zürich

Atmospheric fresh air at rotor inlet

High-pressure exhaust gas delivered from an engine to a rotor inlet

Expansion of exhaust gas provides suction of fresh air

Expanded exhaust gas at a rotor outlet

Pressurized fresh air at a rotor outlet

Pressurized charge air delivered to an engine

Exhaust flange with inlet and outlet orificesAir flange with inlet and

outlet orifices

Rotor driving gear

The pressure transfered from the exhaust gas to the fresh air in a controlled system of narrow channels

The flow control provided by the slide-valve gear

Working Principle of the Standard Pressure Exchanger and its Layout

Rotor as a Key Component

The original design of 34 channels changed to double or even tripple layered

The rotor driven by V-belt from engine crankshaft

Air flange

Shroud

Rotor

Exhaust flange

Rotor drive

Air Inlet

Air Outlet

Exhaust Outlet Exhaust Inlet

1-D Model of a COMPREX® Pressure Exchanger in GT Power

Fresh air inlet AI orifice

Charge air outlet AO orifice

Outlet of exhaust gas and scavenging air EO orifice

Exhaust gas inletEI orifice

Rotor lenght= Rotor diameter

33,8°

108,4°

23,7°

Exhaust FlangeEI orificeEO orifice

Air FlangeAO orificeAI orifice

30,2°

74,5°

17°

26,8°

Control geometry of flange orificesdeveloped to reach the boost pressure of 2 bar at WOT

Double symmetrical orifices to minimize the thermal deformation of a flange

1-D Model of a COMPREX® Pressure Exchanger in GT Power

Var. transmission

Sensor of crankshaft position

1

2

3

4

5

67

8

9

10

11

12

30°

EI orifice

Using of time dependend orifices

for the flow control

Control at Exhaust FlangeControl at Air Flange

VariableTransmissionRatio betweenEngine andCOMPREX

Air Flange Exhaust Flange

Channels

3-Way Catalyst

Intercooler EngineCylindersandManifolds

1-D Model of a COMPREX®

Pressure Exchanger in GT Power

Achieved Results and Model Validation

Basic Shock Wave Theory of a COMPREX® Pressure Exchanger

Exhaustgas

Compressed air Fresh air

u3p3 p0 ;u=0;T 0

A EI

w

Shock Wave of Pressure Ratio Exhaust Inlet Orifice

0

33 p

p

T3; p3

Flow-Rate/Pressure-Ratio Dependence

11

12

3

30

3

33

Tr

Tr

pAm EI

Exhaust Mass Flow Isentropic Exponent for Fresh Air

Reduced Flow Rate ...3

33

p

Tm

Gas Constant

Achieved Results and Model Validation

Comparison of Simplified Model and 1-D Simulation

1,00

1,50

2,00

2,50

3,00

3,50

0 0,5 1 1,5 2

Reduced Exhaust Mass Flow Rate

[kg.s-1.K^0.5/bar]

Exh

aust

Pre

ssu

re R

atio

[1]

Simplified Model

GT Power

Achieved Results and Model Validation

Example of Result Evaluation

Boost Pressure and Exhaust Back Pressure

1

1,5

2

2,5

3

3,5

500 1500 2500 3500 4500 5500

Engine Speed [1/min]

Pre

ssu

re [

bar

]

Boost Pressure

Exhaust BackPressure

Detailed Analysis of Flow and Wave Phenomena inside COMPREX®

1 Cycle

Low-pressure part

High- Pressure part

EI orificeAO orifice

AI orifice

a

b

c'

d

e´

f

g

h

i

j

1

2

3

4

5

6

7

8

9

0

0

b'

c

e

f'g'

d'

Channel

EO orifice

Exhaust Flange Air Flange

Distance

TimeDistance-Time Roadmap and Control Geometry Developed for Boost Pressure of 2bar

Optimal Operaiting Point

Detailed Analysis of Flow and Wave Phenomena inside COMPREX®

-80

-30

20

70

120

170

220

-110 -100 -90 -80 -70 -60 -50

Crankshaft angle [°]

Vel

oci

ty o

f fl

ow

[m

/s]

AO orifice

AI orifice

2

-350

-250

-150

-50

50

150

-110 -100 -90 -80 -70 -60 -50

Crankshaft angle [°]

Vel

oci

ty o

f fl

ow

[m

/s]

EI orifice

EO orifice

68

Idealized shock wave model

WOT boost pressure of 2 bar at engine speed of 3060 rpm

Pressure wave traces chart

1 57

9

Exhaust Flange

Air Flange

Out of Tune Operating Point of COMPREX®

Pockets as Design Solution Improving the Operation Out of the Tune Point

High-Pressure part

Low-Pressure part

Channel

Exhaust Flange

Air Flange

EI orifice

EO orifice

AI orifice

AO orifice

a

b

Compression Pocket

Gas Pocket

Expansion Pocket

Out of Tune Operating Point of COMPREX®

Pocket Modeling in GT Power

Expansion pocket

Compression pocket

Gas pocket

1

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9

6000 11000 16000

Comprex speed [1/min]

Bo

os

t p

res

su

re [

ba

r]

Comprex with pockets

Comprex withoutpockets

Influence of Pockets on the Boost Pressure

Boost Pressure-COMPREX® speed curve at WOT and constant engine speed of 3000 rpm

Optimal COMPREX® speed

Exhaust inlet into gas pocket

Control of gas pocket

Control of comressionpocket

Control of expansion pocket

Out of Tune Operating Point of COMPREX®

Pocket Modeling in GT Power

Gas Pocket in Function of Waste Gate

High-Pressure part

Low-Pressure part

Channel

Exhaust Flange

Air Flange

Compression Pocket

Expansion Pocket

EI orifice

EO orifice

AI orifice

AO orificeWaste Gate

Variable Gas Pocket Control (VGP)

Out of Tune Operating Point of COMPREX®

Pocket Modeling in GT Power

Gas Pocket in Function of Waste Gate

Influence of Art of Control on the Exhaust Back Pressure

0,5

1

1,5

2

2,5

3

3,5

500 1500 2500 3500 4500 5500

Engine speed rpm

Pre

ssu

re [

bar

] boost pressure

exhaust back pressure by WG

exhaust back pressure by VGP

Out of Tune Operating Point of COMPREX®

Pocket Modeling in GT Power

Gas Pocket in Function of Waste Gate

Comparsion of Torque Progress for Different Controls

0

20

40

60

80

100

120

140

160

180

500 1500 2500 3500 4500 5500 6500

Engine speed rpm

To

rgu

e [N

.m]

VGP control

WG control

Conclusions

• Implementation of a COMPREX® Pressure Exchanger into 1-D Engine Model

• GT Power comprehensive object library is sufficient even for this unusual task

• Good agreement with a algebraic model based on the theory of adiabatic shock wave and at least qualitative agreement with published sources

• By implementing COMPREX® model to GT Suite all its features can be fully used