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Aeroderivative Engine PGT25+G4
Why there is no electrical pump in aeroderivative engine?

In aeroderivative engine PGT25+G4, synthetic oil system don't have AC pump to pump the oil to AGB? Why there is no electrical pump, only AGB driven PL-1?

shahba95@gmail.com

shahabas,

Why do you believe it would be beneficial to change the pump driver?

The engine is an aeroderivative engine--meaning that it uses the gas generator section that is typically used for powering aircraft. Do you think it would be a good idea to have a single AC motor-driven oil pump on an engine powering the plane you are flying in?

Mostly, when aero-derivative engines are used for land and marine applications (power generation and propulsion) they use the same gas generator sections (axial compressor and HP turbine section). They are interchangeable, and can be quickly changed out and sent back for service or repair and then returned to one of any number of other locations to produce hot combustion gases for the power turbine (whether it be driving a generator or a propelling a ship).

Would it be possible to reconfigure an aero-derivative gas generator to use an electric motor-driven pump (or two, or three (two AC and one DC)? Yes. But, at what cost? If the Accessory Gear Box-driven pump is acceptable to the engine manufacturer for land and marine use (meaning it meets the safety and protection requirements of warranties), and it doesn't require a new pump system and additional power source(s), why change the system?

I think this question was asked previously on control.com, and I don't recall that it was answered. If you have an application that could benefit from electric motor-driven pumps for the gas generator lube oil pump then if you own the engine you are free to design and implement whatever lubrication delivery system you deem appropriate--as long as you are willing to accept the responsibility of any unforeseen and unaccounted-for knock-on effects.

Aircraft engines have millions of hours of service with only the AGB-driven pump--and the designers and manufacturers of these engines and their lubrication systems would be the first to change if warranty costs and liability forced them to do so. Using an existing design for an application is a tried and proven method to reduce costs and maintain commonality using proven technologies and systems.

Hi sir,

Thanks for your reply.

I have a question, during first startup. How the AGB will lubricate? The PL-1 will pump synthetic oil to AGB after startup only, so it means AGB drive the pump accessories without lubrication?

In a frame machine we have 88QA&88QE for mineral lube oil pumping to starting system, AGB and turbine bearings.

shahabas,

Synthetic oil has some very different properties than hydrocarbon-based "mineral" oil, and one of them is its ability to adhere to surfaces.

The types of bearings used in aircraft derivative engines are usually roller- or ball bearings which don't need the same lubricity during start-up.

Also, the weights of the rotors and the components in the Accessory Gear Box are much lighter in aircraft derivative engines than in heavy duty gas turbines--MUCH lighter. And, so they probably don't require as much lubrication as lower speeds than heavy duty gas turbines do.

I'm NOT an aircraft-derivative gas turbine person--but I can tell you from having flown on hundreds of jets (with aircraft engines) that they all start and run very well with the Accessory Gear Box-driven L.O. pump and synthetic oil. I would imagine, that just like the Accessory Gear Box Main L.O. Pump of GE-design heavy duty gas turbines the oil pump is a positive displacement pump which means it's not a centrifugal pump like the 88QA and 88QE electric motor-driven pumps. Positive displacement pumps put out lots of flow and pressure at very low speeds, and while it may not be enough for starting a heavy duty unit (with HEAVY rotors and journal bearings) it is enough pressure and flow to keep the Emergency (DC) L.O. Pump from starting during a coast-down from rated speed until below 100 RPM.

These are good questions; when considering the answers one has to consider all of the differences between the engines--and the oil used for lubrication, as well as the operating conditions. The two engine types use very different bearings, have very different masses (weights), and employ different oils. And, I believe the Accessory Gear Box-driven oil pump used for most aircraft derivative engines is probably designed to have a high output at low speeds (flow if not also pressure), and probably has some kind of internal compensator to control or limit pressure/flow at higher speeds. Whereas, the pumps driven by electric motors 88QA and 88QE on heavy duty gas turbines are usually centrifugal pumps, which require higher speeds to produce rated flow and pressure.

Hope this helps! You really need to compare the components used in the two types of engines as well as the oil characteristics to fully understand all of the engineering choices made between the two engines. And, by asking these kinds of questions and researching the answers more fully you can be prepared to understand all kinds of different machines as you progress in your career. It's a good exercise to question and delve into the differences. Not all machines require the same auxiliaries, and certainly aircraft engines and aircraft derivative engines are very different from heavy duty gas turbines--even though they might operate on the same principles. A rotary internal combustion engine produces torque that can be used in the same way as the torque produced by a reciprocating internal combustion engine--but they are two very different engines with very different components and characteristics (even though they both do the same thing: produce torque). Aircraft-derivative engines, used as prime movers for generators or compressors or pumps produce torque to drive the generators or compressor or pumps (as opposed to producing thrust to propel an airplane). But, that torque is the same torque as produced by a heavy duty gas turbine engine that can also be used to drive a generator or a compressor or a pump. They're just different types of prime movers--and they don't all have to have the same auxiliaries or components.

Thank you very much sir. I understand perfectly.

While go through p&id, I couldn't understand why the electrical pumps are not in aeroderivative engine for synthetic oil pumping. Now I understand the reason.