Lubrication features of a large diesel engine

Lubrication features of a large diesel engine • In some engines such as long and superlong stroke engines, the piston is not directly connected to the crank pin via a connecting rod. • The piston has a piston rod extending from the bottom of the piston. • The piston rod is then connected to the connecting rod at the crosshead bearing. • The crosshead bearing has a to and fro motion and therefore a continuous hydrodynamic film cannot form. • Therefore oil has to be pumped to the crosshead bearing at a predetermined pressure in order to take the loads of compression and combustion. • The crosshead is connected to the crank pin via a connecting rod. 1

Ref: http: //www. marinediesels. in fo/2_stroke_engine_parts/cr osshead. htm Piston rings Piston skirt Platform separating cylinder from crank case Piston rod Stuffing box Crosshead, crosshead bearing (reciprocating) Oil pumped at a certain pressure Connecting rod Crank pin, bottom end bearing (rotatory motion) Web Journal, journal bearing (rotatory motion) 2

Cylinder liner lubrication • In some engines, lubricating oil in the cylinder is different from the oil supplied to the other bearings. • The cylinder oil contains additives to withstand the high temperatures and contaminants from combustion products. • The oil is slightly basic in nature to counter the acids formed from combustion. • Scraper rings spread the oil over the liner surface. • Lub. oil is usually injected between the two scraper rings. • Oil is injected at a predetermined period during the downward stroke. • Before starting, oil is pumped into the liner by manual priming methods. • After starting, the oil pump is driven by the engine through a cam shaft. 3

Cylinder liner Compression rings Oil injection passage Scraper rings Piston Injection points Cylinder oil pump/lubricator Handle Camshaft 4

Trunk type engine (no piston rod)Splash type lubrication Cylinder liner Piston rings Oil is picked up by the webs while rotating, and splashed onto the piston and liner Gudgeon pin Crank pin, bottom end bearing (rotatory motion) Connecting rod Journal, journal bearing (rotatory motion) Web extension Oil Web 5

Piston rod CROSSHEAD LUBRICATION Telescopic pipes (one moves inside the other) Oil supply Movement of crosshead Crosshead bearing Movement of bearing Stationary pipe Connecting rod 6

Journal bearing Journal Bearing Oil supply The journal bearing may undergo hydrodynamic lubrication or a combination of hydrodynamic and hydrostatic (externally pressurized) lubrication. The oil supply may be from any one or number of positions, depending on the design. 7

Oil passage between bearings in a unit TRUNK TYPE ENGINE Gudgeon pin Connecting rod Crank pin Web Oil passage (drilled) Journal 8

Lubrication system • • TG- Temperature gauge PG- Pressure gauge PG TG ENGINE Shaft Bearings PG Cooler TG PG Storage tank Pump Filter 9 9

Engine sump ENGINE Shaft Bearing Connection for filling the tank Pump Storage tank/sump strainer • The storage tank usually forms the bottom-most compartment of the engine. • It is also sometimes known as the sump. • Oil from the sump is usually transported to the bearings by an engine driven pump or an independently electric motor driven pump that transports the oil to the journal bearings. • Through passages drilled in the crank shaft and webs, it is transported to the crank pin. • Usually a strainer is provided on the suction side of the pump to prevent large contaminant particles from damaging the pump and bearings. 10

Oil cooler- tube and shell type TG PG Oil in TG TG Water in Water out PG PG PG TG Oil out • In this case, cooling water flows through the tubes. • Oil flows in the shell around the tubes and passes the heat to the water. • The in/out temperatures of the oil and water are to be monitored. • Oil pressure is always kept above water pressure to prevent water contamination of oil • However, if there is a leak oil is lost and the sump level is therefore to be monitored 11 regularly

Engine lubrication system Some adverse situations: • • TG- Temperature gauge PG- Pressure gauge • Oil inlet pressure to engine LOW • Oil outlet temperature from engine HIGH • Oil outlet temperature from cooler HIGH PG TG ENGINE Shaft Bearings PG Cooler TG PG Storage tank Pump Filter 12 12

Adverse situations and reasons All pressure and temperature values in a lubrication system have to be constantly monitored • Oil inlet pressure to engine LOW – Filter may be choked blocking flow. – Pump defective. • Oil outlet temperature from engine HIGH – Bearing maybe running hot due to excessive friction. – Leakage of gas from combustion space past piston rings. • Oil outlet temperature from cooler HIGH – Water flow may be restricted due to choked tubes. – Surface of tubes maybe coated with dirt. • Temperature of oil outlet from cooler too LOW (excess viscosity) – Water temperature may be too low- restrict water flow by partially shutting valve. 13

Other maintenance and problem issues With engine is shut down – Oil filters should be cleaned regularly – Cooler tubes to be cleaned Oil level in the sump is to be monitored regularly Low level is indicative of oil leakage somewhere in the system – – Can be at the cooler (oil flowing into water side) At the pump At the valves Check constantly around the engine spaces for accumulation of oil 14

Lubricating oil pumps Lubrication pumps are positive displacement pumps– They supply a definite amount of fluid for each cycle of rotation regardless of resistance which may oppose the transfer. – They do not need any initial priming Different types are: • Reciprocating – Piston, plunger • Rotary – Vane, piston, screw, gear, lobe and screw 15

Reciprocating piston pump Ref: http: //www. lcresources. com/resources/getstart/pump. gif • In a reciprocating pump, a volume of liquid is drawn into the cylinder through the suction valve on the intake stroke and is discharged under positive pressure through the outlet valves on the discharge stroke. • The discharge from a reciprocating pump is pulsating and changes only when the speed of the pump is changed. • Often an air chamber is connected on the discharge side of the pump to provide a more even flow by evening out the pressure surges. Reciprocating pumps are often used for sludge and slurry. 16

Gear pump • Consists of two meshing gear wheels housed in a tight fit casing. The gears rotate in opposite directions and the vacuum created due to this, draws the fluid into the inlet side of the pump. The fluid is trapped in the spaces between the teeth and casing to be carried round from the suction to the delivery side Fluid is displaced when gear teeth mesh Therefore there is a continuous transfer of liquid from suction to delivery side The theoretical volume displacement is given by • • • § do = outside diameter dr = root diameter N = rps w = depth of gear perpendicular to the screen • • • 17