Presentation on theme: "1 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."— Presentation transcript:
1 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.
2 Piston Piston rod Crank pin, bottom end bearing (rotatory motion) Journal, journal bearing (rotatory motion) Crosshead, crosshead bearing (reciprocating) Connecting rod Piston rings Oil pumped at a certain pressure Ref: fo/2_stroke_engine_parts/cr osshead.htm Web Piston skirt Stuffing box Platform separating cylinder from crank case
3 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.
5 Trunk type engine (no piston rod)- Splash type lubrication Piston rings Web Crank pin, bottom end bearing (rotatory motion) Connecting rod Gudgeon pin Cylinder liner Journal, journal bearing (rotatory motion) Web extension Oil Oil is picked up by the webs while rotating, and splashed onto the piston and liner
6 Telescopic pipes (one moves inside the other) Piston rod Movement of crosshead Movement of bearing Connecting rod Stationary pipe Oil supply CROSSHEAD LUBRICATION Crosshead bearing
7 Journal bearing Journal Bearing 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. Oil supply
8 Oil passage between bearings in a unit Web Journal Crank pin Oil passage (drilled) Connecting rod Gudgeon pin TRUNK TYPE ENGINE
9 9 Lubrication system TG- Temperature gauge PG- Pressure gauge ENGINEShaft Cooler Storage tank Pump Filter Bearings PG TGPG TG
10 Storage tank/sump Engine sump ENGINEShaft Bearing 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. Pump Connection for filling the tank strainer
11 Oil cooler- tube and shell type Oil in Oil out Water inWater out TG 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 regularly PG
12 Engine lubrication system TG- Temperature gauge PG- Pressure gauge ENGINEShaft Cooler Storage tank Pump Filter Bearings PG TGPG TG Some adverse situations: Oil inlet pressure to engine LOW Oil outlet temperature from engine HIGH Oil outlet temperature from cooler HIGH
13 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.
14 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
15 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
16 Reciprocating piston pump 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. Ref:
17 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 d o = outside diameter d r = root diameter N = rps w = depth of gear perpendicular to the screen