Turbine Engine Lubrication

A turbine engine is characterized as a complex machine that consists of a lot of systems and subsystems, which are all needed in order for the machine to operate in unison as a multifaceted integrated entity. Lubrication plays a huge role in a high-power rotating machine such as a turbine engine. The engine lubrication system has the major objective of reducing wear and friction of moving and non-moving parts of the turbine engine. Moreover, the lubrication system helps in cooling as needed by the bearing systems. The reduction of overall frictional force is achieved through the introduction of a viscous liquid that is capable of separating two surfaces that come into contact when a machine is operational. The absence of lubrication results in increased generation of frictional heating. Lowering of heat generation occurs when lubricant flows at the bearing interfaces while physical contact is reduced at a rapid rate in bearing surfaces (MacIsaac & Langton, 2011). This paper is a discussion on the concepts of lubricating and cooling through the turbine engine lubrication system.

Lubrication will ensure that oil reaches locations where sliding and rolling contact occurs on the engine bearings. The appropriate lubricant to be applied on surfaces or bearings depend on the ratio of heat generation together with dissipation. The analysis of the heat generation process that pertains to a typical bearing arrangement entails a complex analysis task of calculating movements and forces that are involved with the bearing’s elements. When lubricant is used as coolant, this brings about a practical method of cooling turbine engine bearings (Linke-Diesinger, 2008).

Continuous lubrication of bearings occurs through the delivery of oil while using pressurized jets that are assisted by centrifugal effect that comes from the bearing rotation. Varying mixtures of oil delivery and cooling passages define the mechanisms in which a turbine engine’s bearings are lubricated. Within the turbine engine’s bearings lubrication oil is removed quickly and also as completely as possible in order to maximize the cooling effect. Lubricants used in lubrication and cooling of engine bearings ought to have a viscosity of 15,000 centistokes (cSt) at -400 c together with a pour point at-540 c. Moreover, the lubricant should have a viscosity that ensures the maintaining of the Elasto-Hydro-Dynamic (EHD). Oxidative stability is an important attribute of lubricants since at elevated levels, there will be change in viscosity due to break down and forming of free radicals (Podevin, Clenci & Descombes, 2011).

Cooling requirements and EHD film thicknesses dictate bearing lubrication needs. In accordance with cooling requirements, sophisticated design practices propose that lubrication oil be delivered into the bearings through jets that have been located within the bearing housing, and afterwards, the oil has to be scavenged away from the bearings as fast as possible. While in the bearing housing, the residency of the oil is very short since the oil has to be limited to a temperature of 250C (Lin et al., 2014).

Turbine engines have oil tanks that offer reservoir of oil available to the lubrication system. The engine bearings receive oil through a high-pressure pump that obtains de-aerated fuel that has come from the oil tank. Additionally, the engine bearings together with the accessory gearbox are supplied by the primary oil supply referred to as oil supply pump. Before the oil reaches the bearing system, it is filtered by an oil filter. A pressure transducer, which is monitored by the full-authority digital electronic control (FADEC) is fitted in the lubrication system to aid in ensuring that the oil flows downstream from the main supply pump. The advanced lubrication delivery and cooling system, have been able remove several hundred horsepower heat from matching gear surfaces (Linke-Diesinger, 2008).

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    MacIsaac, B., & Langton, R. (2011). Gas turbine propulsion systems. Chichester, West Sussex: Wiley.