Presentation on theme: "Lubrication features of a large diesel engine"— 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 Platform separating cylinder from crank case PistonRef:Piston ringsPiston skirtPiston rodPlatform separating cylinder from crank caseStuffing boxCrosshead, crosshead bearing (reciprocating)Oil pumped at a certain pressureConnecting rodCrank pin, bottom end bearing (rotatory motion)Journal, journal bearing (rotatory motion)Web
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 Cylinder linerPiston ringsOil is picked up by the webs while rotating, and splashed onto the piston and linerGudgeon pinConnecting rodCrank pin, bottom end bearing (rotatory motion)Journal, journal bearing (rotatory motion)Web extensionOilWeb
6 CROSSHEAD LUBRICATION Piston rodTelescopic pipes (one moves inside the other)Oil supplyMovement of crossheadCrosshead bearingMovement of bearingStationary pipeConnecting rod
7 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.
8 Oil passage between bearings in a unit TRUNK TYPE ENGINEGudgeon pinConnecting rodCrank pinWebJournalOil passage (drilled)
9 Lubrication system TG- Temperature gauge PG- Pressure gauge ENGINE ShaftBearingsPGCoolerTGPGStorage tankPumpFilter99
10 Engine sump ENGINE Shaft Bearing Connection for filling the tank Pump Storage tank/sumpstrainerThe 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.
11 Oil cooler- tube and shell type Oil inPGTGTGTGWater inWater outPGPGPGTGOil outIn 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 oilHowever, if there is a leak oil is lost and the sump level is therefore to be monitored regularly
12 Engine lubrication system Some adverse situations:Oil inlet pressure to engine LOWOil outlet temperature from engine HIGHOil outlet temperature from cooler HIGHTG- Temperature gaugePG- Pressure gaugeTGPGENGINEShaftBearingsPGCoolerTGPGStorage tankPumpFilter1212
13 Adverse situations and reasons All pressure and temperature values in a lubrication system have to be constantly monitoredOil inlet pressure to engine LOWFilter may be choked blocking flow.Pump defective.Oil outlet temperature from engine HIGHBearing maybe running hot due to excessive friction.Leakage of gas from combustion space past piston rings.Oil outlet temperature from cooler HIGHWater 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 downOil filters should be cleaned regularlyCooler tubes to be cleanedOil level in the sump is to be monitored regularlyLow level is indicative of oil leakage somewhere in the systemCan be at the cooler (oil flowing into water side)At the pumpAt the valvesCheck constantly around the engine spaces for accumulation of oil
15 Lubricating oil pumpsLubrication 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 primingDifferent types are:ReciprocatingPiston, plungerRotaryVane, piston, screw, gear, lobe and screw
16 Reciprocating piston pump Ref: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.
17 Gear pumpConsists 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 sideFluid is displaced when gear teeth meshTherefore there is a continuous transfer of liquid from suction to delivery sideThe theoretical volume displacement is given bydo = outside diameterdr = root diameterN = rpsw = depth of gear perpendicular to the screen