Active Damping of Torsional Vibrations of Internal Combustion. Engines.
Department of ... retrieve the cylinder-wise torque contributions of the engine. Fig.
5. ... This project was done in cooperation with and financed by. Wärtsilä Finland
Oy ...
Active Damping of Torsional Vibrations of Internal Combustion Engines Department of Information Technologies Faculty of Technology Åbo Akademi University Fredrik Östman and Hannu Toivonen
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[email protected] Introduction
The benefits are: Cylinder-wise gas torque
For large medium-speed engines – used in power plants and marine propulsion applications – stricter demands on emission control and performance are addressed by new computer-controlled techniques, such as common-rail fuel injection, dual fuel techniques, etc.
• the dynamics of the crankshaft can be taken into account
40 35
• time varying dynamics can be incorporated in the engine model
Torque [kNm]
30 25 20 15
• reduces the need of parameter management for large engine portfolios
10 5 0
Generator 0
20
40 60 F requency [ Hz]
80
100
Experimental Results Flywheel
Crankshaft dynamics -100 Gai n [dB]
Cylinder balancing experiments have been performed on a six-cylinder 6 MW Wärtsilä W6L46CR engine at the engine laboratory in Vaasa, cf. Fig. 7 and 8.
Full-sc ale Flywheel Full-sc ale Load R educ ed Flywheel R educ ed Load
-150 -200
10
0
1
2
10
10 Freque nc y [Hz]
Phase [deg]
0
-200
-400 10
0
1
2
10
10 Freque nc y [Hz]
Engine
Fig. 1. Common-rail fuel injection system.
Fig. 3. Fuel combustion excitations of a six cylinder engine
Electronically controlled fuel-injection techniques provide today essential means for optimizing the performance and emissions of fuel-combustion process of internal combustion engines. Due to varying dynamics and ageing of components of the fuel-injection systems, there may be a significant dispersion of the injected cylinder-wise fuel amounts. As the resulting discrepancy between the cylinder-wise torque contributions increases torsional vibrations of the crankshaft, it is important to continuously monitor and calibrate the fuel injections
2
1
K1
K2
C1
C2
Fig. 7. Wärtsilä W46CR engine
Problem Formulation 6000
The objectives of the project are to:
• Retrieve information of the relative cylinder-wise torque profile from the reconstructed gas torque
The oscillating gas torque M can be calculated from measurements of the angular speeds from both sides of the flexible coupling as
J1
• Adjust the cylinder-wise fuel injections in such a way that the torsional vibrations of the crankshaft are minimized.
5000
J2
1
2
1 dJ1 2 d 1 D2
2
Torque [Nm]
• Reconstruct the superposed oscillating gas torque applied on the flywheel from measurements of angular speed of the crankshaft
Fig. 4. Engine-generator model.
Order 1/2 Order 1 Order 3/2
a
4000 3000 2000 1000 0
0
2
4
6 Iteration
8
10
12
4
6 Iterations
8
10
12
Cyl 1
2 1
C2
D1 2
1
K2
C1 (
1
C1 (
2
2
) K1 (
1
2
1
) K1 (
2
1
)
Cyl 2
M 2
) ML
Cyl3
600 Duration offset [µs]
G e e r a t o r
By assuming that the crankshaft is rigid, the enginegenerator set can be represented by a two-mass lumped model, cf. Fig. 4.
b
Cyl 4 Cyl 5 Cyl 6
400 200 0 -200 -400
CCM
By using the engine-specific phase-angle diagrams which relate each excited order to the consecutive cylinder firings, the lowest torque frequencies can be analyzed in order to retrieve the cylinder-wise torque contributions of the engine.
CCM
Rotor speed
Flywheel speed
1
Coupling
2 Rotor
Fig. 2. Cylinder balancing device.
3 6
of a six cylinder engine.
Angular speed measurement of flywheel Angular speed measurement of load
Fig.8. Tests on 20% engine load
In comparison with automotive engines, cylinder balancing of large medium-speed engines requires different approaches in order to successfully minimize torsional vibrations. By, moreover, using adaptive approaches the convergence rate improves significantly.
Fig. 5. Phase-angle diagram for frequency order 1/2
Reconstruction of superposed torque The behavior of the flywheel is mainly dependent on the cylinder-wise torque excitations, how the crankshaft dynamics filters these excitations and the dynamics of the flexible coupling, cf. Fig. 3.
2
Conclusions 5
4
Generator
0
Acknowledgements This project was done in cooperation with and financed by Wärtsilä Finland Oy – R&D through two TEKES projects and one EU framework 6 project.
For the purpose of cylinder balancing the theoretical phaseangle diagrams can be used if the crankshaft can be assumed rigid for the analyzed orders.
Publications Östman, F, and Toivonen, H T. (2008). Active control of torsional vibrations of reciprocating engines, Control Engineering Practice, 16, pp. 78 – 88.
For engines where theoretical phase diagrams are inaccurate, an adaptive approach has also been developed where the phase-angle diagrams of the engine is determined by using online updates, cf. Fig 6.
Östman F. and Toivonen H.T. (2008). Model-based Torsional Vibration Control of Internal Combustion Engines. IET Control Theory & Applications (in press).
Reconstruction of superposed torque
FFT
Determination of the cylinderwise influence on the torsional vibrations
Cylinder-wise fuel
Calculating individual fuel injection adjustment
Adaptive engine model
Fig. 6. Block diagram of the cylinder balancing method.
injection adjustment
