The principles of aircraft engine lubrication

It is understood that to keep competitive and protect their investment in equipment, enterprises in the aircraft industry require lubrication solutions of the highest quality at the best possible prices. While specialist lubricants for the sector are designed to ensure that system components can move freely and efficiently, they must also tick multiple boxes.

Reducing wear and tear from friction and excessive heat in aviation engines, they are also required to clean and cool engines while acting as a sealant against contamination and corrosive forces. Rust protection can be especially important when fleets are used infrequently, as unused aircraft are at high risk from corrosive elements during spells of downtime.

In this article, we’ll take you on an in-depth examination of the most important principles of aircraft engine lubrication. Read on to find out more.

Lubricating the aircraft engine

The first quality most people consider when it comes to a lubricant is, naturally, its lubricating properties. Effective lubrication always requires an oil film that is both strong and thick enough between moving components to keep wear and friction to an absolute minimum.

Oil properties may include hydrodynamic, dynamic, mixed film or boundary forms.

Mixed-film or boundary lubrication is used in the aircraft engine’s upper cylinder area within its outer boundary. This point is the most remote area of the engine requiring lubrication, as the oil rings take most of the oil film from the cylinder walls before it ever ascends to the upper cylinder. There must always be a residual amount of lubricant in the upper cylinder so that the engine is protected on start up.

If an engine is left idle, some lifters may be pressed and loaded with maximum spring pressure. In such cases, most of the lubricant has been squeezed from the junction. As a result, when the aircraft engine starts, it takes time to get oil to where it is required. Therefore, a good boundary oil film is necessary.

Dynamic lubrication comes from the pressure generated by the oil pump. This pressure delivers a sufficient flow of oil to the lubricating system. Hydrodynamic lubrication offers a smooth surface for moving parts to operate on and prevents direct contact occurring between moving parts.

In hydrodynamic lubrication, contact pressure is kept lower and spread over a greater surface area. As a result, a constant supply of oil is necessary between the components for hydro-dynamic lubrication.

Lubricants must clean aircraft engines

All oils designed for the aviation industry can clean. This concept commonly conjures the removal of varnish, sludge and other accumulated deposits on the plugs in the dedicated oil pan, or within the screen. There are additional benefits to this process, however, for aircraft operators. When lubricants keep an aircraft engine clean, they also clean the ring belt area to ensure that the combustion process is kept under better control. When these rings can move freely, an airplane engine will operate at higher efficiencies and has enhanced ring seal. It also produces far less blow-by and will consume less oil.

A ring belt that remains dirty will restrain the fluid movement of the engine rings within their grooves and, as a result, they cannot seal. Resultantly, pressure is often created between the cylinder wall and the ring face, leading to scuffing, scarring and undue wear.

How aviation lubrication keeps engines cooler

Air-cooled airplane engines depend on the oil that they use for cooling more than automotive engines cooled by water. As a rule, automotive oil commonly accounts for around 40 per cent of the cooling capacity required, but in aviation engines, oils must be relied upon to carry off a far greater percentage of heat from the engine.

Oil acts as a heat-transfer medium and flows via the crankcase and dedicated oil coolers, and as it flows, it dissipates the heat from all moving components, continually cooling piston rings and engine bearings.

Without the cylinder wall being cooled by this film of oil film, the rings would have a poor heat transfer path. As a result, issues like melting, scarring and galling can occur. Engine oil also cools the entire valve train and its valve springs.

Oil as a sealant in aircraft engines

Finally, oil creates a seal between cylinder walls and the rings, but also assists by sealing the rubber and synthetic seals and gasketed areas for the engine’s crankshaft. When the oil flows around those areas, it works to retain the seal. For this reason, aviation oil must always involve a formulation that is fully compatible with an engine’s seal materials to extend the active service life of seals.

When the correct aviation engine lubricant is selected for a specific make and model of engine, all these principles will be sufficiently satisfied. As a result, aircraft operators can enjoy maximum performance from a well-protected engine.

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