Presentation on theme: "Lubrication Lubrication of diesel engine has two purpose: 1.to lubricate 2.to remove heat The lubricating oil is taken from a drain tank usually underneath."— Presentation transcript:
Lubrication Lubrication of diesel engine has two purpose: 1.to lubricate 2.to remove heat The lubricating oil is taken from a drain tank usually underneath the engine by a screw or gear pump. It is cooled, filtered and supplied to the engine by an inlet oil pipe rail at a pressure of approx. 4 bar.
Lubrication of a trunk type engine The luboil is supplied to the main bearings of the crankshaft through drillings in the frame of the engine. Through drilled passages of the crankshaft, the luboil flows to the crankpins and bottom end bearings. The luboil is then led through drilled passage of connecting rod to piston gudgeon pins and top end bearings. From top end bearing the luboil is led to underneath of piston crown for cooling and then it drops back into the crankcase.
The cylinder liner and piston rings must also be lubricated. This luboil is supplied by “splash” from luboil leaving rotating bottom end bearing after lubricating the bottom end bearings. Oil scraper rings scrape most of the splashed oil, but some oil which escapes the scraping action is spread up and down the surface of the liner by the piston rings.
Some large trunk type engines also have cylinder oil being supplied to the liner under pressure by separate pumps. The oil is led to the liner through drillings, where grooves distribute it circumferentially. The piston rings spread it up and down the surface of the liner.
Cylinder Luboil functions 1.Lubricate piston rings and liner to minimize wear of both 2.Provide a film of oil between piston ring and liner to seal gases of combustion space from crankcase 3.To neutralize acidic products of combustion so that corrosion of liners and bearings may be prevented
Luboil is also supplied to the rocker gear which operates the inlet and exhaust valves and the cams and camshaft bearings. Some times this part of lubrication is kept separate from lubrication mentioned above to minimize contamination of leaky fuel getting into the main crankcase luboil.
A pre luboil pump is sometimes fitted, especially to engines where the main luboil pump is engine driven.. This pump is electrically driven and circulates the luboil around the engine prior to starting.
Lubrication of a crosshead type engine Luboil is supplied to main bearings, camshaft and camshaft bearings. A separate supply is led via a swinging arm or a telescopic pipe to the crosshead, where some of it is diverted to cool the piston (traveling up and back through the piston rod) and whilst some is used to lubricate the crosshead bearing and guides and the rest is led to the bottom end bearing or crankpin bearing via a drilling in the connecting rod. Lub oil may also be used to operate the hydraulic exhaust valves. On some engines the luboil led to the crosshead is boosted to 16 bars by another pump in series. This luboil is also used to operate the hydraulic reversing gear.
The cylinder liners of crosshead type of engines are lubricated by a separate set of injection pumps, which use a different specification of oil. The oil is led to the liner through drillings, where grooves distribute it circumferentially. The piston rings spread it up and down the surface of the liner. This luboil has same functions as stated above for separate cylinder lubrication of trunk type engines.
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.
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
The fine adjustment operates in such a way 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 camshaft less 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 and 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.