Turbochargers & Bulk

[KJ_Lesnick]

wuzak

The GE Form 13 turbocharger was redesignated B-1 at soem point in the late 1930s. This was then developed into subsequent B-series turbos.

Okay

The Form 10 turbosupercharger (and the Form 8 turbo on which the F-10 was based) had a reversed compressor impeller. That is, instead of the air being drawn in through the very end of the turbo, as in B-series and modern car turbos, the air was drawn in between the compressor and turbine housings.

Why the hell would you want to mount the impeller that way?

Yes

Why would you use that?  Wouldn't that require you to carry more coolant onboard and being that you could never re-use it you'd end up wasting it all?


Hobbes

This is basic physics

I know that, but sometimes people become so enmeshed in the complicated that they forget basic fundamentals.

It's possible that aviation engine designers were unaware of the work done on air compressors, but IMO not that likely.

So they understood most likely

The reason intercoolers aren't used on gas turbines is they move huge amounts of air.

Well that's an air to air intercooler...

An intercooler large enough to cool all that air is very large and would add a lot of drag, not to mention all the piping creates lots of air resistance for the compressed air.

Even a liquid-air cooled design?  For the most part I'm glad they went without them for simplicity sake.

[wuzak]

[

The Form 10 turbosupercharger (and the Form 8 turbo on which the F-10 was based) had a reversed compressor impeller. That is, instead of the air being drawn in through the very end of the turbo, as in B-series and modern car turbos, the air was drawn in between the compressor and turbine housings.

Why the hell would you want to mount the impeller that way?

The idea was that the intake air would be drawn in across the turbo's main bearings, and thus providing a cooling effect.

[KJ_Lesnick]

The idea was that the intake air would be drawn in across the turbo's main bearings, and thus providing a cooling effect.

Understood -- I still think making things as simple as possible is generally a good idea whenever possible.

[wuzak]

Yes

Why would you use that?  Wouldn't that require you to carry more coolant onboard and being that you could never re-use it you'd end up wasting it all?

The compromise is that a small extra tank of liquid (water/methanol) is carried instead of a (heavier) intercooler, associated plumbig and its coolant. Not to mention that there is no drag because no extra radiators are required.

The downside is that the amount of time that can be run at high boost is much reduced. Typically a WW2 era piston engine would spend only a small amount of time at such powers anyway. There will, theoretically, be some loss of efficiency comapred to intercooled engines at lower powers.

The reason intercoolers aren't used on gas turbines is they move huge amounts of air.

Well that's an air to air intercooler...

An intercooler large enough to cool all that air is very large and would add a lot of drag, not to mention all the piping creates lots of air resistance for the compressed air.

Even a liquid-air cooled design?  For the most part I'm glad they went without them for simplicity sake.

You have to look at he main reason why intercoolers are used on piston engines - detonation. Piston engines have a limit to how much boost/compression they can run, and it is to do with pre-ignition or detonation. And that is partly to do with how hot the charge is when it enters the cylinder.

In trubines the problems of pre-ignition and detonation do not exist, because turbines are continuous burn engines.

In theory better efficiencies can be gained in turbines by heating the intake air. German scientists developed heat exchangers for turboprops precisely for that reason, though I don't think any actually flew. They also have the disadvantage of increasing drag on an aircraft, so they weren't applied to jets.

That said, some modern turboprops are fitted with ADI to aid in take-off on hot days. This allows more compression, which means more fuel and more power, but less efficiency.

[KJ_Lesnick]

wuzak

The compromise is that a small extra tank of liquid (water/methanol) is carried instead of a (heavier) intercooler, associated plumbig and its coolant. Not to mention that there is no drag because no extra radiators are required.

I don't want to come off as answering a question with a question, but does this still work well for a long-range escort fighter or a bomber?  I'm assuming there's eventually a point where the intercooler and radiator produces less range-penalty than the water-methanol coolant carried []i](extreme range where you'd have to carry prodigious amount of coolant)[/i].

In trubines the problems of pre-ignition and detonation do not exist, because turbines are continuous burn engines.

So Nathan Price in his L-1000/XJ37 engine used intercooling merely as a way to keep turbine temps low even with high pressure ratios and increase density to further amp performance?

[wuzak]

In trubines the problems of pre-ignition and detonation do not exist, because turbines are continuous burn engines.

So Nathan Price in his L-1000/XJ37 engine used intercooling merely as a way to keep turbine temps low even with high pressure ratios and increase density to further amp performance?

Intercooling in turbines does allow for higher compression ratios, therefore more air, more fuel and more power. The compressor would be more efficient, but not the turbine itself.