Optical investigation of the effect of composition on the atomisation of marine diesel engine oil

Following on from a preliminary study commissioned by BP and completed at the University of Brighton in April 2011, BP funded further research to better understand the effect of lubricating oil composition on the spray formation and cylinder wall coverage of marine diesel engine oil.

Objectives
The approach for the experimental work was similar to the preliminary study carried out by the University of Brighton.

The main objectives were:
- To carry out a comprehensive literature review on the problem domain
- To build a test rig
- To gather experimental data relating to spray formation and coverage using highspeed video
- To develop algorithms for extracting droplet size, coverage pattern and other relevant characteristics from the experimental data
- To analyse and compare the measured parameters as a function of lubricant composition and describe any significant differences
During the experimental phase of the work, the oil spray was observed in both free air
and as it impinged on a Perspex cylinder liner.

The University designed and built a test rigs which, along with the injector and injector
driver supplied by BP, allowed the visualisation of oil sprays at atmospheric conditions. Where the research examined spray impingement onto a Perspex Liner, the approach enabled the investigation of the effect of lubricant properties on oil coverage. The oil was heated in order to obtain a viscosity comparable to normal running conditions. The cylinder section was manufactured using an acrylic sheet in order to facilitate optical access.

This simple approach facilitated the investigation of the effect of lubricant properties
on spray formation and atomisation. The oil was heated in order to obtain a viscosity
comparable to normal running conditions. The morphology of the spray, droplets and
ligaments were studied by digital imaging and high-speed video.

This approach aimed to indicate whether the various lubricants produce different bulk spray patterns, droplet sizes and ligament morphology.

The data set was expected to consist in high-speed videos of the liquid phase of the spray,
recorded at a frame rate of 21,000 fps from the start of injection and a resolution of
approximately 1280 x 240 pixels (exact frame rate and resolution to be defined during
testing). A minimum of 50 data sets were gathered for each lubricant, to offer statistical
significance and information on shot-to-shot variability.

The behaviour of these sprays was shown to vary significantly, ranging from a wind-induced breakup through to atomisation. The full range of test viscosities, 20-140 cSt, could feasibly be seen with standard lubricants in an operating engine. It is significant then that some regimes would be particularly unsuitable for distribution into the swirl-air of a running engine, resulting in small droplets entrained within the air and leaving with the exhaust.

Results were published in the PhD thesis associated with the project, "Optical investigation into the effect of lubricant composition on spray lubrication in marine diesel engines" by Dr Timothy Christopher Gardhouse