Synthetic lubricating oil is frequently used in modern gas turbine engines because, compared to lubricating oil made from mineral oil, it is better able to withstand high-temperature levels. Since modern gas turbine engines operate at temperatures higher than 260 degrees Celsius, the lubricating oil used in these engines tends to break down into its component molecules, which can negatively impact the machine’s performance.
Because of this, a tiny amount of the oil will often evaporate, leaving behind a residue consisting of carbon and gum. Furthermore, as the oil is heated to higher degrees, its ability to act as a lubricant becomes less effective.
Many sub-categories can be applied to synthetic oil, but the Type I synthetic lubricating oil is the one that has the most widespread acceptance. Type I oil, and the MIL-L-7808 were the results of early research conducted by the military on developing a lubricating oil that could sustain high temperatures for an extended time without exceeding its capabilities. At first, it was demonstrated that Type I, alkyl diester oil, worked effectively; but, in the late 1950s and early 1960s, more powerful engines were developed. These new engines operate at a higher temperature, and machines that use Type I oil are more likely to acquire heavy oil deposits, which require prompt repair in the event that they occur.
Because of this, a new kind of synthetic lubricating oil known as Type II oil was developed as a result. It was generally agreed that Type II polyester-based synthetic oils, also known as MIL-L-23699, achieved the greatest level of success both technically and financially. This synthetic oil is also referred to as a 5-centistoke oil. This designation indicates that the oil needs to have a kinematic viscosity of at least 5 cSt when heated to 99 degrees Celsius. This criterion enables the oil to maintain a sufficient body at a range of operating temperatures in order to carry all loads that are applied.
In most cases, the benefits of using synthetic oil in turbine engines exceed the drawbacks of using synthetic oils, such as the difficulty and expense involved in producing synthetic oils. As a result of using synthetic lubricating oil, not only was the service life of the lubricant extended, but it also reduced the formation of carbon deposits on the engine and strengthened the engine’s protection against wear. As a result, the cost of maintenance was reduced.
Since the early 1960s, type II oil has been widely utilized and serves as the foundation for modern jet oils. Several engines have attempted to push the limits of type II oil and have tested its capabilities. However, the pursuit of developing powerful engines is one that never ends. In addition to this, the materials of the engine components have been revolutionized through the use of composite materials in order to achieve lightweight technology. This technological advancement makes it possible to produce new generations of lubricating oils. The third generation and the fourth generation were both created by different businesses in an effort to boost load carrying capabilities, as well as improve lubricating qualities and performance.
The Mobil Jet Oil 254 is an example of lubricating oil that belongs to the third generation. When compared to a regular type II oil, this particular form of lubricant possesses superior qualities in terms of its resistance to deterioration and deposit control, as well as an extraordinary high-temperature thermal stability, as stated by Exxon Mobil Corporation (2022). In addition to this, they improve the oil’s resistance to foaming and can cut the rate of oxidation in the bulk of the oil by up to half.
Here are some examples of lubricating oils used in gas turbine engines and their advantages and disadvantages:
AeroShell Turbine Engine Oil 500
Aeroshell Turbine Oil 500 is a 5 mm synthetic hindered ester oil incorporating a carefully selected and balanced combination of additives to improve thermal and oxidation stability and metal passivation.
- Improves thermal and oxidation stability
- Approved in a wide range of turbine engines
- Contains a synthetic ester oil
- Not stable for High thermal uses
Mobil Jet Oil II
Mobile Jet Oil II is a high-performance aircraft-type gas turbine lubricant formulated with a combination of a highly stable synthetic base fluid and a unique chemical additive package. The combination provides outstanding thermal and oxidative stability to resist deterioration and deposit formation in both the liquid and vapor phases, as well as excellent resistance to foaming The effective operating range of Mobil Jet Oil II is between -40 ºC (-40 ºF) and 204 ºC (400 ºF) Mobil Jet Oil II is engineered for aircraft gas turbine engines used in commercial and military service requiring MIL-PRF-23699G Type STD level performance. It also is recommended for aircraft-type gas turbine engines in industrial or marine service applications.
- Suitable for a wide range of severe operating conditions
- High specific heat
- Excellent bulk oil stability
- Not suitable for mixing with other products
- Turbo Oil 2389
The Type of engine that you are utilizing should determine whether or not you use oil from the third generation. Although a regular type II lubricating oil is regarded to be more affordable, third-generation oil is considered to be more expensive; yet, its efficiency and efficacy can be seen when applied to current and powerful engines. It allows the engine to start up and ensures effective lubrication of critical components even when the temperature is low, which are some of the advantages it has over a standard type II lubricant. Other advantages include the reduction
of the formation of carbon and sludge deposits, the reduction of engine maintenance, the extension of the life of seals, gears, and bearings, the reduction of evaporation losses, and the reduction of oil consumption.
Despite the fact that lubricating oils of the fourth generation are still thought to be in the process of being developed, it is expected that the power of lubricating oils of the fourth generation will continue to increase. The Mobil Jet Oil 291 is an example of lubricating oil that belongs to the fourth generation.
However, engine manufacturers such as CFM international and Honeywell have issued a service bulletin regarding carbonization that can be found on valves and seals during routine checks. Another problem that is filed under the same lubricating oil is corrosion, particularly in the O-rings, due to the fluorosilicates. It was described by the Exxon Mobil Corporation as providing superior thermal and oxidation stability. The oil system developed a leak as a direct result of the corrosion.
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