Timed cylinder lubrication

Cylinder lubrication should be injected in carefully metered amounts. The injection points should be spaced around the periphery in such a way as to ensure adequate coverage when the piston passes the feed points. The best timing for injection is suggested as being between the first and second rings. The difficulties in achieving this are great, but injecting at TDC and to a lesser extent BDC assists

Lubrication is of the total loss system i.e. the oil is expected to be completely combusted without residue. The oil is injected through quills which pass through the liner wall.

Cylinder lub oil properties

The type of cyl l.o. required will depend upon the cylinder conditions and the engine design e.g crosshead or trunk piston. However, the property requirements are basically the same but will vary in degree depending upon the fuel and operating conditions.

Normal properties required are;

1. adequate viscosity at working temperature so that the oil spreads over the liner surface to provide a tough film which resists the scrapper action of the piston rings
2. the oil must provide an effective seal between the rings and liner
3. only a soft deposit must be formed when the oil burns
4. alkalinity level (total base number or TBN) must match the acidity of the oil being burnt
5. detergent and dispersant properties are required in order to hold deposits in suspension and thus keep surfaces clean

Behaviour depends upon the temperature of the liner, piston crown and piston rings. TBN and detergency are closely linked. This can have an adverse effect when running on lighter fuels with lower sulphur content for any period of time. Coke deposits are can increase.

Consequences of under and over lubricating

Over lubrication will lead to excessive deposit build up generally in the form of carbon deposits. This can lead to sticking of rings causing blowpast and loss of performance, build up in the underpiston spaces leading to scavenge fires, blockage and loss of performance of Turboblowers as well as other plant further up the flue such as waste heat recovery unit and power turbines.

Under lubrication can lead to metal to metal contact between liners causing microseizure or scuffing. Excessive liner and piston wear as well as a form of wear not only associated with under lubrication but also with inadequate lubrication called cloverleafing

Causes

1. Insufficient cyl l.o
2. Incorrect cyl l.o.
3. Blocked quill
4. Incorrect cyl at each stroke.

The fine adjustment operates in such away that by screwing it in the stroke of each pump may be accurately metered. Additionally it may be pushed into give a stroke enabling each p/p to be tested. The eccentric stroke adjuster acts as a coarse adjustment for all the pumps in the block. Additionally it may be rotated to operate all the pumps, as is the case when the engine is pre-lubricated before starting. Correct operation of the injection pumps whilst the engine is running can be carried out by observing the movement of the ball

Electronic cylinder lubrication

Exact injection timing of cylinder lube oil is essential for efficiency. A move to electronics for the control of this has been made by some large slow speed engine manufacturers.

The system is based on an injector which injects a specific volume of oil into each cylinder on each ( though more normally alternate) revolution of the engine. Oil is supplied to the injector via a pump or pumps. A computer, which is synchronised to the engine at TDC each revolution, finitely controls the timing . Generally most efficient period for lubrication is taken at the point when the top rings are adjacent to the injection points.

The injection period is governed by the opening of a return or 'dump' solenoid which relieves system pressure.

Quantity can be adjusted by manually limiting the stroke of the main lubricator piston, by altering the injection period or by the use of multiple mini-injections per revolution.

The high degree of accuracy with this system allows for lower oil consumption rates.

Shown is the injector unit fitted to modern camshaftless slow speed engines. The motive force is via a dedicated or common hydraulic system. The hydraulic piston acts on multiple plungers one for each quill. At the dedicated time the electric solenoid valve energises an allows hydraulic oil to act on the piston commencing oil injection. One or two pumps per unit may be fitted dependent on cylinder diameter and oil flow requirements.

Precise control of the timing of injection allows oil to be delivered into the ring pack, something which has proved impossible with mechanical means. This has reduced oil consumption by as much as 50%.
Pre- lubrication for starting may be built into the bridge remote control system or carried out manually.

Cylinder lubricator quill