Oil Recommendation for a Jet Engine Project

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sgvaibhav

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Hi,

I needed oil recommendation for my graduation project.
We are making a jet engine from an automobile turbocharger.

So oil will be required to lubricate the turbo (of course :P) and to keep the turbo cool as well (oil cooled).

I needed recommendation for oil weight.
is there anything higher than 20W60?
 
I'd personally use a Mobil 1 product, and probably 5w30...the turbine should be balanced, and not adding huge bearing loads...if it's ball bearing, then even less need for thick.

Just get the cooling right.
 
You are making a centrifugal flow compressor. Concern yourself with adequate flow and large sump capacity. Use light alloy for sump design to aid in heat dissipation.

I'd choose some type of PAO or PAO/Ester in the Xw-30/Xw-40 range. A synthetic motorcycle oil might be a good choice.

Detergents and high TBN fluids aren't required for applications like this. Oils that deal with oxidation and nitration are.

What do you plan to use for fuel?
 
I believe his theory is to make a gas turbine engine. The term "jet" is just a common nomenclature. Whether it's axial, centrifugal, or axial-centrifugal is not the issue here.

While the reactive propulsion will be minimal, the term 'jet' would still apply to this project.
 
Originally Posted By: EricG
Are you converting the turbocharger into an axial flow design? Otherwise, its not a "Jet" engine!


That's not entirely correct. Frank Whittle's first jet engine had a centrifugal flow compressor with an axial flow turbine. I don't know of any jet engines with radial-flow turbines, however. But that's not to say that it can't be done. There are plenty of examples on You Tube of people that have built jet engines out of turbochargers.

At one point in my career, I worked on an automotive gas turbine at Allison that had radial-flow turbines; one to run the compressor, and a separate one to propel the car. The thrust from a simple-cycle turbojet engine is produced by accelerating the exhaust gases through a nozzle. I think the drawback of centrifugal-flow turbines in jet applications is the flow field at the outlet of the turbine probably has less component of flow in the direction of motion as an axial flow turbine.

If you could find a turbocharger with a centrifugal compressor and an axial flow turbine, it would probably yield a more efficent jet engine. EMD locomotive engines use that type of a turbocharger, and there are probably other examples on large diesel engines.

As far as an oil recommendation is concerned, I would say some Red Line product, maybe their 0w20 or 20WT racing oil. The best thing to do would be to send a personal message to Tom_NJ. If I'm remembering correctly, he designs ester lubes for gas turbine engines.
 
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Originally Posted By: FowVay
I believe his theory is to make a gas turbine engine. The term "jet" is just a common nomenclature. Whether it's axial, centrifugal, or axial-centrifugal is not the issue here.

While the reactive propulsion will be minimal, the term 'jet' would still apply to this project.
+ 1
 
Originally Posted By: EricG
Are you converting the turbocharger into an axial flow design? Otherwise, its not a "Jet" engine!
Whittle's turbines were not axial and that design flew in everything from the Bell jet prototype to the Mig 15. The Brits gave the communists the plans for the Rolls engine.
 
Originally Posted By: Shannow
I'd personally use a Mobil 1 product, and probably 5w30...the turbine should be balanced, and not adding huge bearing loads...if it's ball bearing, then even less need for thick.

Just get the cooling right.


Yup its a ball bearing.
Its an Garret - GT 4502R, so its really huge.

Originally Posted By: FowVay

What do you plan to use for fuel?

Initial plan was Propane, but it was changed to LPG later.


Basically jet engines found in aircraft use axial compressor/turbine for space considerations.

This project will instead use a radial compressor/turbine by using an automobile turbocharger.
Thrust is generated, by accelerating hot gases through a nozzle. Since Newton's third law applies for here thrust generation, I guess it can be considered a jet engine.


...
Starting the engine can be critical and adequate lubrication at low rpm/starting is a priority when the oil temperature might be around 25 deg C.
We will be using 4 liters of oil in the sump for the turbo to manage heat transfer and ensure that oil doesn't get overheated, since temperatures are expected to reach about 700 deg C in the turbine.
Looking at these range of temperatures, i was thinking of 10W60.
But does a 10W40 and 10W60 have similar viscosity at engine starting condition (25 deg C)? - because i dont want a very thick oil at starting, and i dont want oil to break up because of high temperatures.

Suggestions guys...
laugh.gif
 
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The polyol ester based turbine oils used in commercial jet engines are very light (less than a 0W-16) and have only mild anti-wear properties as there is very little load. Not sure how suitable these would be for a modified automotive turbo charger. They can certainly take the heat, but load must be considered.

Typical physical properties are:

Viscosity @ 100°C: 5.1 cSt
Viscosity @ 40°C: 25 cSt
Viscosity @ -40°C: Viscosity Index: 135
Pour Point: -57°C
Flash Point: 260°C
Noack Volatility: 4%
Density @ 15.5°C: .993 g/ml

The most thermally stable of the commercial jet engine oils is Air BP 2197. If more load carrying is needed, AeroShell 555 may do the trick provided there are no silicone seals. Of course no oil will handle 700°C but I doubt the oil itself is seeing those temperatures. If you need extreme presure, Redline 0W-20 or 30 can be considered.

Hopefully you will be able to trial your lubricant choice and monitor frequently with oil analysis.

Tom NJ
 
Originally Posted By: sgvaibhav
Yup its a ball bearing.
Its an Garret - GT 4502R, so its really huge.

Suggestions guys...
laugh.gif



Since you're using a ball-bearing turbo, maybe a dedicated gas turbine oil wouldn't be a bad choice.
 
Quote:
Starting the engine can be critical and adequate lubrication at low rpm/starting is a priority when the oil temperature might be around 25 deg C.

We will be using 4 liters of oil in the sump for the turbo to manage heat transfer and ensure that oil doesn't get overheated, since temperatures are expected to reach about 700 deg C in the turbine.


As Tom said, I doubt the oil will see 700C. And glad to see that you are using a heat exchanger to cool the oil.

One of the things one should do is a thermodynamic analysis of the system as part of your paper or thesis. This will show you understand the thermodynamics of your design.

Start with the temps expected as a result of the combustion chemistry, then heat paths via conduction, then you will be able to determine oil flow and cooling requirements in order to size your heat exchanger and any air flow needed through the heat exchanger.

Determining your temps at the bearings will be critical in your design and success. As an example, bearing cells in axial flow jet engines will see the highest temps in the turbine bearing cells because of heat conduction from the burner cans or annular burners.

I second Tom's suggestion to start with a lubricant that has a polyol component to the base oil for temperature stability, such as Redline's 20 weight or 30 weight oils.

It seems the only unknown here is bearing loads. Hopefully, you have done radial and axial loads analysis to determine that.

What RPM are you expecting?

One of the rules of thumb for bearing lubrication is that for bearings with light loads and high rpm, you use a low viscosity oil, and that for low rpm's and high loads you use a high viscosity lubricant.
 
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I will take the suggestion of gas turbine oils into consideration.
Some similar projects we reviewed were carried out with smaller turbo's and they used automotive oils.
Since we are also using an high performance"automobile turbocharger", we are little inclined to using automotive oils.
I guess we will go with 0W30 or 5W30.
If temperature sensor shows very high temperatures, we will switch to a higher grade oil (such as 10W-40 or 10W-60)

Originally Posted By: MolaKule

As Tom said, I doubt the oil will see 700C. And glad to see that you are using a heat exchanger to cool the oil.

One of the things one should do is a thermodynamic analysis of the system as part of your paper or thesis. This will show you understand the thermodynamics of your design.

Start with the temps expected as a result of the combustion chemistry, then heat paths via conduction, then you will be able to determine oil flow and cooling requirements in order to size your heat exchanger and any air flow needed through the heat exchanger.

Determining your temps at the bearings will be critical in your design and success. As an example, bearing cells in axial flow jet engines will see the highest temps in the turbine bearing cells because of heat conduction from the burner cans or annular burners.

I second Tom's suggestion to start with a lubricant that has a polyol component to the base oil for temperature stability, such as Redline's 20 weight or 30 weight oils.

It seems the only unknown here is bearing loads. Hopefully, you have done radial and axial loads analysis to determine that.

What RPM are you expecting?

One of the rules of thumb for bearing lubrication is that for bearings with light loads and high rpm, you use a low viscosity oil, and that for low rpm's and high loads you use a high viscosity lubricant.



Yes, there wouldn't be 700 deg C at the bearing, or no oil would satisfy the requirements.
Thanks for idea of thermodynamic analysis of system. I will consider that.

We have installed a temperature sensor from the oil outlet, to monitor operation and help us with oil selection IF we face any troubles.

We never thought of determining bearing loads.

The rpm range is between 55,000 rpm (self sustaining start point) to 109,000 rpm (MAX).
 
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It also couldn't hurt to send an e-mail to Garrett to get their recommendations for oil. You could also ask them what their balance specification for that turbo is and calculate a max expected radial load based on that. The high shaft speeds of turbochargers require very precise balancing, probably on a par with gas turbines. After all, Garrett makes gas turbine engines, too.
 
Originally Posted By: Tom NJ
The polyol ester based turbine oils used in commercial jet engines are very light (less than a 0W-16) and have only mild anti-wear properties as there is very little load. Not sure how suitable these would be for a modified automotive turbo charger. They can certainly take the heat, but load must be considered.

Typical physical properties are:

Viscosity @ 100°C: 5.1 cSt
Viscosity @ 40°C: 25 cSt
Viscosity @ -40°C: Viscosity Index: 135
Pour Point: -57°C
Flash Point: 260°C
Noack Volatility: 4%
Density @ 15.5°C: .993 g/ml

The most thermally stable of the commercial jet engine oils is Air BP 2197. If more load carrying is needed, AeroShell 555 may do the trick provided there are no silicone seals. Of course no oil will handle 700°C but I doubt the oil itself is seeing those temperatures. If you need extreme presure, Redline 0W-20 or 30 can be considered.

Hopefully you will be able to trial your lubricant choice and monitor frequently with oil analysis.
Tom NJ

As Tom suggests a jet engine oil is likely the way to go.
In a POE/PAO motor oil like Red Line their 10wt race oil (spec's below) would most closely match the characteristic of a jet engine oil:

KV100 5.2cSt
KV40 27.2cSt
VI 130
NOACK 6%
Flash Pt 215C

http://www.redlineoil.com/product.aspx?pid=12&pcid=1
 
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