1. GAS EXCHANGE IN INTERNAL COMBUSTION ENGINES
MTZ Conference – Engine
7th and 8th November 2007 Stuttgart
Gas Exchange in a
Combustion Engine
An Example 

2. Accurate determination of important
gas exchange parameters directly at the test bed based on existing measured values
Dr. Robert Fairbrother, development simulation GCA
Dipl.-Ing. Fernando Moreno Nevado, development gasoline engines,
Franz Hirschmann, development GUI-GCA,
Dr. Thomas Leifert, product management GCA
AVL List GmbH

3. GCA contents Principle Analysis Combustion Gas exchange Losses
Indicating
contents
Test Bed
Principle
Analysis
Combustion
Gas exchange
Losses
Test bed: an example
Conclusion
GCA
Simulation

4. AVL GCA : Working Principle and Motivation
At the test bed
Exhaust pressure curve
Intake pressure curve
Cylinder pressure curve

5. AVL GCA : Working Principle and Motivation
At the test bed
Exhaust pressure curve
Intake pressure curve
Cylinder pressure curve
In the simulation
Reduced AVL BOOST Model
Combustion analysis
Highly relevant, non-measurable in-cylinder parameters are made available (e.g. internal AGR).
- Accuracy high  - Calibrating effort low  - Calculation time low 

6. Workflow

7. Combustion Analysis

8. GCA_C_Valve_Lift_Intake GCA_C_Valve_Lift_Exhaust
Gas Exchange Analysis
Presssures & Flows
GCA_C_Valve_Lift_Intake
GCA_C_Valve_Lift_Exhaust
GCA_C_*_Exhaust_Boundary
e.g.
GCA_C_Pressure_Exhaust_Boundary
GCA_C_*_Intake_Boundary
e.g.
GCA_C_Pressure_Intake_Boundary
GCA_C_*_Intake
e.g. GCA_C_Pressure_Intake
GCA_C_*_Exhaust
e.g. GCA_C_Pressure_Exhaust
GCA_C_Mass_Flow_Intake
GCA_C_Mass_Flow_Exhaust
BURN_C_ROHR
(Only values after start of combustion are used and are normalized by BOOST)
GCA_C_ROHR
GCA_C_Pressure

9. Loss Analysis Ideal engine Real charge Combustion position Unburned
Burn profile (ROHR)
Mixture properties
Wall heat
Blow by
Ideal gas exchange
Real gas exchange

10. EXAMPLE VALVE OVERLAPING
Valve overlapping:
20 deg CA
Exhaust
Intake
valve lift
Exhaust
Intake
mass flow

11. EXAMPLE VALVE OVERLAPING
Valve overlapping:
30 deg CA
Exhaust
Intake
valve lift
Exhaust
Intake
mass flow

12. EXAMPLE VALVE OVERLAPING
Valve overlapping:
40 deg CA
Exhaust
Intake
valve lift
Exhaust
Intake
mass flow

13. EXAMPLE VALVE OVERLAPING
Valve overlapping:
50 deg CA
Exhaust
Intake
valve lift
Exhaust
Intake
mass flow

14. EXAMPLE VALVE OVERLAPING
Valve overlapping:
60 deg CA
Exhaust
Intake
valve lift
Exhaust
Intake
mass flow

15. RESULTS AT SPEED 2000 rpm, BMEP = 2 bar,  = 1
-7%
Increasing valve overlaping means:
Increase of total mass and residual gas at IVC
Lower amount of fresh charge
Increase of residual gas content
Lower specific fuel consumption
Increase of efficiency

16. SOLUTION: LOSS ANALYSIS
Mixture properties
Wall heat
Efficiency
+2%

17. WALL HEAT LOSS

18. MIXTURE PROPERTIES k k - 1  k  cp = • R cp hth valve overlaping time
60 °KW
20 °KW
specific heat cp kJ
kg • K
= 0, p = 10 bar
l = p = 1 bar
temperature K
Temperature K k cp
k - 1 =
• R 1 V , th - = k e h cp  k 
hth

19. CONCLUSION
Accurate determination of important gas exchange parameters
directly at the test bed based on existing measured values 2%
AVL-GCA