Modelling and Cavitation Discrepancy Analysis of Multi-Cylinder Engine Based on Variational Mode Decomposition (VMD)

Variations in liner vibration among cylinders can lead to non-uniform lubrication, accelerated wear, and cavitation in multi-cylinder diesel engines. This study investigated the origin of these variations in a heavy-duty straight-six diesel engine using a transient dynamic model of the cylinder assembly, modal analysis, and VMD. An elastic transient model of the block, liner, and piston system was developed with measured cylinder pressure, cylinder head bolt preload, and piston thermal deformation applied as boundary conditions. The model was validated against modal testing and bench measurements of liner acceleration. Under nominally identical piston excitation across all six cylinders, the computed liner responses were decomposed using VMD to extract intrinsic mode components and dominant frequency bands. The results show that the primary vibration response is concentrated in the upper-middle region of the liner, while the end cylinders exhibit higher vibration levels than the central cylinders. A dominant component centred at approximately 1800 Hz is identified and linked to an engine block mode whose spatial deformation pattern matches the cylinder-to-cylinder distribution of liner vibration and cavitation risk. These findings indicate that the inter-cylinder discrepancy is linked to engine block modal and non-uniformity constraints. The proposed model provides a basis for reliability-oriented mitigation of vibration and cavitation in multi-cylinder diesel engines.