Piston Engine Propulsion

Oil

• Lubrication oil is often considered to be the life blood of an engine. Without it, the friction and wear produced between moving parts would cause an engine to wear at a very rapid rate.

• In addition to reducing friction, lubricating oil is responsible for removing a great deal of engine heat.

• In fact, without an ample supply of oil, most reciprocating engines will overheat. Additional functions of lubricating oils include creating a seal between moving parts, cushioning impact forces created by combustion, cleaning the engine, and protecting against corrosion.

• The purpose of a lubrication system is to supply oil at the correct pressure and volume to provide adequate lubrication and cooling for all parts of the engine, which are subject to the effects of friction.

• The lubrication is distributed to the engine moving parts by pressure, splash, and spray.

• Pressure lubrication is the primary type of lubrication used in reciprocating engines.

• All pressure lubrication systems rely on a pump to supply pressurized oil to critical engine parts.

• The movement of the internal components, which splash oil around, produces splash lubrication.

• Spray lubrication uses the same pressurized oil in a pressure lubrication system, however, instead of routing the oil to a component through an oil passage, the oil is sprayed on to a component through a nozzle.

• Reciprocating engine lubrication systems are generally classified as either:

• wet-sump or • dry-sump system

Wet Sump

• With a wet sump system, all the oil is carried in the engine crankcase.

• With this type of system, the oil is picked up by a pump and distributed throughout the engine.

• Once the oil has circulated, it drains down into the sump where it is picked up and recirculated.

SUMP

Engine Block‘WET’ SUMP SYSTEM

FilterPump

Common for most vehicles

SUMP

Engine Block‘DRY’ SUMP SYSTEM

FilterPump

High Performance/Rally vehicles and Aircraft

Tank Scavenge Pump

Dry Sump• Dry-sump systems differ from wet-sump

systems in that the oil is stored in a separate oil tank.

• This type allows a large quantity of oil to be carried.

• This makes dry-sump systems well suited to large radial engines.

• This type of system needs a scavenge pump to pump the oil back to the tank.

A typical pressure lubrication system consists of an:

• oil reservoir, • oil pump, • scavenge pump, • oil pressure relief valve, • oil filter, • oil cooler, • and all the necessary piping and connections.

Filters

• There are two types of filtration systems that may be installed in aircraft piston engines;

• They are the full flow filter system• and the by-pass or partial flow system.

• With the full flow system all of the oil passes though the filter each time it circulates the engine.

• To accomplish this the filter is installed in series between the pump and the bearings.

• The by-pass system is installed in parallel with the engine bearings.

• In this type of system, only about 10 percent of the oil is filtered each time the oil circulates through the system.

• However over time, the entire oil supply will pass through the filter

Let’s take a closer look at what happens here

TYPICAL OIL SYSTEM – Distribution

Front Bearing Support

Rear Bearing Support

Bearing Support

Bearing Support

Bearing Support

TYPICAL OIL SYSTEM – Bearing Locations/Lubrication

No 1 Piston

1

No 2 Piston

2

No 3 Piston

3

No 4 Piston

4

CRANKSHAFT FROM A 4 CYLINDER ENGINE

Oil Splash

Oil Splash

Oil Splash Oil

Splash

Crankshaft Internal Oil Feed

Plain Bearing

TYPICAL OIL SYSTEM – Bearing Lubrication

Oil Distribution Groove

Lubricating Oil Film

Con Rod Big End