AbstractLow-speed marine diesel engines are among the largest reciprocating engines in the world, with cylinder bores up to 1 m and strokes of up to 3.5 m. Traditional lubrication systems use low pressure quills to introduce lubricant into the cylinder, spread circumferentially by a zig-zag liner groove and vertically by the piston rings. The scale of these engines means getting proper lubrication to the top of the cylinder is a challenge, made more significant by the additional role of marine diesel cylinder lubricants (MDCLs) as a neutralising agent for the sulphuric acid produced when combusting the high-sulphur content fuel that powers these engines. There is a tendency to over-lubricate the cylinder to ensure that what lubricant reaches the top of liner is sufficient. A new generation of marine lubrication systems has been developed that use much higher pressures and spray nozzles in place of quills, which allows lubricant to be targeted to a region of the liner directly.
MDCLs are formulated for the traditional lubrication systems. This work investigates lubricant behaviour in a modern spray lubrication system using highspeed optical imaging techniques. Two experimental facilities have been developed: The first having the goal to replicate in-engine geometry (including liner) and hydraulic supply properties, and the second taking a more fundamental approach using a constant delivery pressure and an optical nozzle to understand the root causes of spray behaviours seen in the first test facility. A range of oils were tested, primarily based upon commercial MDCL compositions, but also using simplified blends to isolate lubricant properties. With no other literature available in this specific field, a phenomenological model has been developed based upon behaviour observed within the optical nozzle, in the near-nozzle region, in the free spray, and on arrival at the liner. This model has then been compared to work in the heavily researched field of spray breakup.
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.
|Date of Award||Jan 2021|
|Supervisor||Cyril Crua (Supervisor) & Guillaume De Sercey (Supervisor)|