Abstract

Cylinder lubrication oil is essential for efficiently operating large two-stroke diesel engines, reducing friction and wear by creating a thin film between moving surfaces. This study examines a spray lubrication system that delivers oil into the swirling scavenging air within the cylinder by a lubrication oil injector, crucial for effective coverage at the cylinder's top. With a growing emphasis on optimizing oil consumption to lower emissions and operational expenses, this PhD thesis aims to deepen understanding of spray lubrication systems by exploring scavenging air dynamics, spray breakup, and other factors affecting oil flow through the injection nozzle.

Using Computational Fluid Dynamics (CFD) with OpenFOAM, the scavenging process in a uni-flow two-stroke diesel engine is simulated, incorporating dynamic meshing to account for piston motion. The lubrication injectors are experimentally characterised using the Bosch rate of injection technique, revealing a buildup time of approximately 1 ms before cavitation affects the flow, with an accurate prediction of injected mass within a 5% error margin.

The experimental data is fed to the CFD model to reveal the spray movement in the scavenging air. A parametric study of injection angles is performed and shows optimal oil distribution and the significance of droplet size distribution in controlling mass trapped in the air swirl. Further investigations into spray breakup processes are done to enhance understanding of how the droplet size distribution is formed.

In summary, this research enhances understanding of spray lubrication processes, identifying key variables and areas for focus.