Lubrication features of a large diesel engine

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
Ref http//www.marinediesels.info/2_stroke_engine
_parts/crosshead.htm
Piston rings
Piston skirt
Piston rod
Platform separating cylinder from crank case
Stuffing box
Crosshead, crosshead bearing (reciprocating)
Oil pumped at a certain pressure
Connecting rod
Crank 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.

4
Cylinder liner
Compression rings
Scraper rings
Oil injection passage
Piston
Injection points
Cylinder oil pump/lubricator
Handle
Camshaft
5
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
Connecting rod
Crank pin, bottom end bearing (rotatory motion)
Journal, journal bearing (rotatory motion)
Web extension
Web
Oil
6
CROSSHEAD LUBRICATION
Piston rod
Telescopic pipes (one moves inside the other)
Oil supply
Movement of crosshead
Crosshead bearing
Movement of bearing
Stationary pipe
Connecting 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 ENGINE
Gudgeon pin
Connecting rod
Crank pin
Web
Journal
Oil passage (drilled)
9
Lubrication system

• TG- Temperature gauge
• PG- Pressure gauge

ENGINE
Shaft
Bearings
Cooler
Storage tank
Pump
Filter
9
10
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.

11
Oil cooler- tube and shell type
Oil in
Water in
Water out
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 regularly

12
Engine lubrication system

• Some adverse situations
• Oil inlet pressure to engine LOW
• Oil outlet temperature from engine HIGH
• Oil outlet temperature from cooler HIGH

• TG- Temperature gauge
• PG- Pressure gauge

ENGINE
Shaft
Bearings
Cooler
Storage tank
Pump
Filter
12
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
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.

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
• do outside diameter
• dr root diameter
• N rps
• w depth of gear perpendicular to the screen