Lubrication Part 2 - Aircraft Gas Turbine Engines #23

Summary

The video script explains the intricacies of the lubrication system in gas turbine engines, focusing on gear tight pumps for oil delivery and retrieval. It details the use of multiple scavenge pumps to maintain a dry sump system and the importance of oil coolers, which can be air or fuel-cooled. The script also covers oil temperature regulation, oil cooler matrix assembly, and the prevention of oil starvation with bypass valves. Additionally, it discusses chip detectors for early failure detection and the role of filters and strainers in debris management. The necessity for synthetic oils with specific properties, such as low volatility and high film strength, is highlighted for optimal engine performance.

Takeaways

• 🔧 Gear tight pumps with intermeshing steel gears are used for oil delivery and retrieval in recirculate systems.
• 🛠️ Oil pumps, both pressure and scavenge, are mounted on the accessory housing and are part of an oil pump pack, which can include up to seven scavenge pumps.
• 💧 Multiple scavenge pumps help maintain a dry sump system for the lubrication system.
• 🌡️ Oil coolers can be air-cooled or fuel-cooled, and some engines use both methods to regulate oil temperature effectively.
• 🔁 A fuel-cooled oil cooler warms up cold fuel and cools hot oil, achieving dual benefits.
• 🚫 An oil bypass valve in the fuel-cooled oil cooler prevents oil starvation and damage from excess pressure by allowing oil to bypass a blocked cooler.
• 🛑 Chip detectors and magnet plugs in scavenge lines collect ferrous material, indicating potential bearing failures.
• 🌀 A centrifugal breather in the accessory drive unit separates oil from air, minimizing oil loss and maintaining engine lubrication.
• 🛡️ Filters and strainers within the lubrication system prevent debris circulation and ensure oil cleanliness.
• 🛢️ Early gas turbine engines used mineral-based oils, but synthetic oils were developed to handle higher temperatures and speeds, offering better performance.

Q & A

What is the primary function of gear tight pumps in a recirculating oil system?

Gear tight pumps are used for delivering and retrieving oil in a recirculating system by rotating gears that draw oil into the pump, carry it around by the teeth, and deliver it at the outlet.

Why are multiple scavenge pumps used in an oil pump pack?

Multiple scavenge pumps are used to ensure that the lubrication system remains a dry sump system, which helps in maintaining efficient oil circulation and prevents oil from accumulating at the bottom of the sump.

How does an oil cooler work, and what are the two types mentioned in the script?

An oil cooler works by exchanging heat from one medium to another, typically using a matrix assembly with baffle plates to ensure maximum cooling effect. The two types mentioned are air-cooled and fuel-cooled oil coolers.

What is the purpose of the oil bypass valve in a fuel-cooled oil cooler?

The oil bypass valve is designed to prevent oil starvation in the engine and to protect the matrix assembly from damage due to excess oil pressure by allowing oil to bypass the cooler if it becomes blocked.

How does the pressure maintaining valve prevent fuel from entering the oil system in case of damage to the oil cooler matrix?

The pressure maintaining valve keeps the oil pressure higher than the fuel pressure, so in the event of damage to the oil cooler matrix, oil will leak into the fuel system rather than fuel entering the oil system.

What is the role of chip detectors in the lubrication system?

Chip detectors, which are permanent and magnet plugs, collect ferrous material from the oil as it returns to the scavenge pumps. This helps in detecting potential bearing failures by monitoring for metal contamination in the oil.

Why is it important to vent the interior of the engine to the atmosphere?

Venting the interior of the engine to the atmosphere is important to prevent excessive air pressure within the accessory drive unit and bearing chambers, and to manage airborne oil droplets that form an oil mist.

How does a centrifugal breather minimize oil loss in a gas turbine engine?

A centrifugal breather minimizes oil loss by spinning at high speed to separate oil from air using centrifugal force, flinging the oil back into the accessory drive unit and allowing clean air to escape to the atmosphere.

What is the purpose of filters and strainers in the lubrication system?

Filters and strainers are used to prevent debris and foreign matter from being circulated continuously with the oil, ensuring clean oil reaches critical engine components.

What are the key properties of synthetic oils used in gas turbine engines?

Synthetic oils used in gas turbine engines have properties such as low volatility, high flash point, high film strength, a wide temperature range, low viscosity, and a high viscosity index to ensure efficient lubrication under various conditions.

Why are gas turbine engines invariably dry sump engines, and when should the oil level be checked?

Gas turbine engines are dry sump engines to facilitate efficient oil circulation and to prevent oil from accumulating at the bottom of the sump. The oil level should be checked immediately after engine shutdown or within a specified time after shutdown.