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