Some more drawings of the FW190C

[koivis]

Originally Posted by swiss

Not really, the P47 just had a turbo/IC setup - but they called it "exhaust-supercharger" which adds to the confusion.

Well, actually it was a similar system to Fw 190C. As far as I know, every P&W R-2800 made also had an internal supercharger mounted directly behind the engine, driven by the crankshaft. The confusing thing here is, that while the air from turbocharger went indeed to the carburetor, from there it continued to the supercharger! After that, it's of course going to cylinders. Some pictures to clarify:

P-47 Engine, supercharger in blue colour, carburetor is the black thing on top of it:


Another view, showing the duct leading to carb, blue object is the supercharger:


Rolls Royce Merlin had almost the same setup (I think most WW2 engines did), except it had an liquid cooled intercooler as the last thing before the intake. Also of note here (two stage version) is that the air is cooled between the stages too!


Hope this helps, I get sometimes confused with this technology too.

[T}{OR]

Originally Posted by swiss

Great, we finally agree.

Yeah.

Originally Posted by swiss

But I still dont get Turbo->SC.
It says they used an additional turbo, but nowhere a modified charger, which they probably had to, since it had to deal with altered pressure.
Also, I thought SC work with lower pressure compared to turbos.
Plus, the SC is fed with (still)hot air and heats its up again.
I have some doubts concerning efficiency, what is the SC's purpose? Reduce IC lag?

I guess I'll have to do some research.

I am guessing it has something to do along the lines what Azimech wrote:

Originally Posted by Azimech

... It seems they had it right to keep the supercharger attached to the engine, since the turbo takes load of from it, decreasing the load on the engine to drive the supercharger, and being able to boost even more. It was probably even coupled with the barometric device that regulated the variable hydraulic clutch. Anyway I would've chosen that spot due to the CoG.

On the second thought...

Originally Posted by koivis

Well, actually it was a similar system to Fw 190C. As far as I know, every P&W R-2800 made also had an internal supercharger mounted directly behind the engine, driven by the crankshaft. The confusing thing here is, that while the air from turbocharger went indeed to the carburetor, from there it continued to the supercharger! After that, it's of course going to cylinders.

Now that makes no sense. A supercharger compressing a mixture of air and fuel?! What was the compression ratio inside the cylinders then (ε)?

Unless... Doh! But of course. I am 90% sure this is a Pressure Carburetor since allied engines didn't have fuel injection. So you could say this was a form of fuel injection - to prevent negative G cutouts. Or at least has something to do with how Pressure Carburetor functions.

Question here is - is Fw-190C using proper mechanical fuel injection or a Pressure Carburetor as well?

Originally Posted by koivis

Rolls Royce Merlin had almost the same setup (I think most WW2 engines did), except it had an liquid cooled intercooler as the last thing before the intake. Also of note here (two stage version) is that the air is cooled between the stages too!

As it should be, or else you risk injecting too hot air inside the cylinder. Merlins had to have a mechanically driven SC because their exhaust was - almost non-existent.


A very interesting thread if I may say so!

[T}{OR]

After skimming through this document:

http://faculty.sdmiramar.edu/wnorth/249/249six.pdf

I am not so sure what this last supercharger is for. If someone can provide more accurate drawings maybe it will be more clear. I can't make out exactly how it works from the pictures posted.

And the added bonus is the fact it is already and hour past midnight here. So I will continue this discussion tomorrow.

EDIT: Something like this:

[koivis]

Originally Posted by T}{OR

I am not so sure what this last supercharger is for.

It's for supercharging the engine! (sarcasm) Well, really, if there wasn't a supercharger, the engine would probably put out considerably less power. The only reason why such large engines have internal superchargers is because otherwise, they would need to be even bigger. Without it, there would be less air turning the turbo, and it would provide less boost. I'm not aware of any WW2 aircraft having only a turbosupercharger without a normal, crankshaft driven one.

If this sounds stupid, it could be because it's way past midnight here too.

Originally Posted by T}{OR

The reason for "added" complexity:

http://en.wikipedia.org/wiki/Turbo-compound_engine

Yes, exactly! I read that article, just used the Dobrynin as an example as even a bit more complex than R-3350 TC. Napier Nomad is another case, you simply cannot describe that one (atleast thefirst version) without a picture or two.

You have to remember that the first turboprops and turbojets were considerably less fuel efficient than the turbo-compounds, and for the same power, while the TC probably weighed twice (or more) as much, it still burned much less fuel. That's why Canadair Argus changed to R-3350 TC from Bristol Proteus, and why the big piston airliners (Starliner, DC-7) soldiered on for so long. It was the weight and complexity that killed them, and the more advanced (two-spool) or larger (Kuznetsov NK-12!) turboprops in development.

[Azimech]

Thor, the reason the carburettor was placed on top of the supercharger in allied engines was that it increased the efficiency of the supercharger due to the cooling of the air due to vaporisation of the fuel. This was the main reason Rolls Royce chose the carb over fuel injection, because they considered it. On big radials the supercharger has the bonus of better distribution of the mixture to the cilinders.

Koivis, amazing find! I don't mind offtopic if it's about beautiful technology (and huge and absurdly complex engines )

For fun you should see diagrams of the oil distribution system in big radials, it looks like spaghetti XD

Okay, here's a BIG ONE:

[swiss]

Now it's really getting confusing.
That SC in pics of the p47 engine looks like it's driven by the crankshaft.
So it's not a turbo-compound-engine(of which I didn't even know they exist until tonight) - or am I wrong?

Back to the 190

... It seems they had it right to keep the supercharger attached to the engine, since the turbo takes load of from it, decreasing the load on the engine to drive the supercharger, and being able to boost even more. It was probably even coupled with the barometric device that regulated the variable hydraulic clutch. Anyway I would've chosen that spot due to the CoG.

Concerning the power draw of the sc:
Does it matter whether it compresses:
-ambient air to Xpsi
vs
-X psi to ?X psi
It needs to "work" either way, no?




And then there's the heat issue again.
While googling I found this neat little calculator I'd like to share: http://www.stealth316.com/2-turbotemp.htm
Of course there are a ton of factors, but at least it's a start.

I used a pressure of 4.37psi@10k
Temp: -58°F
source:
http://sydney.edu.au/engineering/aer...ere/atmtab.txt
http://www.engineeringtoolbox.com/ai...ure-d_462.html

Whatever I tried, the results in the Intake manifold, after the SC, were actually worse then directly after the turbo.
Maybe I'm reading wrong though.

[T}{OR]

Originally Posted by koivis

You have to remember that the first turboprops and turbojets were considerably less fuel efficient than the turbo-compounds, and for the same power, while the TC probably weighed twice (or more) as much, it still burned much less fuel. That's why Canadair Argus changed to R-3350 TC from Bristol Proteus, and why the big piston airliners (Starliner, DC-7) soldiered on for so long. It was the weight and complexity that killed them, and the more advanced (two-spool) or larger (Kuznetsov NK-12!) turboprops in development.

Very interesting stuff, I agree.

Indeed early Turbos were indeed heavy. Last month I was in BMW's Museum in Munich - the comparison in size between F1 turbochargers back in '70s and today is astonishing. Today you can basically just 'attach' it to the exhaust manifold lol.

Originally Posted by Azimech

Thor, the reason the carburettor was placed on top of the supercharger in allied engines was that it increased the efficiency of the supercharger due to the cooling of the air due to vaporisation of the fuel. This was the main reason Rolls Royce chose the carb over fuel injection, because they considered it. On big radials the supercharger has the bonus of better distribution of the mixture to the cilinders.

For fun you should see diagrams of the oil distribution system in big radials, it looks like spaghetti XD

It really did look to me as if there was a bonus of better mixture distribution (on the P&W R-2800) if you put another compressor behind the Carburetor. I forgot about the fuel vaporisation.

LOL, a proper spaghetti indeed. Reminds me of the cross section of an automatic gearbox.

Originally Posted by swiss

Now it's really getting confusing.
That SC in pics of the p47 engine looks like it's driven by the crankshaft.
So it's not a turbo-compound-engine(of which I didn't even know they exist until tonight) - or am I wrong?

No I don't think it is. A turbo compound engine would have a turbine for power recovery on the exhaust section.

SC is indeed driven by the crankshaft. That was my point of confusion as well...

Originally Posted by swiss

Concerning the power draw of the sc:
Does it matter whether it compresses:
-ambient air to Xpsi
vs
-X psi to ?X psi
It needs to "work" either way, no?

You mean X to Y psi?

By either way do you mean: X => Y & Y => X, or ambient to X & X to Y?

It will compress whatever you input first, to a certain ratio.

Originally Posted by swiss

And then there's the heat issue again.
While googling I found this neat little calculator I'd like to share: http://www.stealth316.com/2-turbotemp.htm
Of course there are a ton of factors, but at least it's a start.

I used a pressure of 4.37psi@10k
Temp: -58°F
source:
http://sydney.edu.au/engineering/aer...ere/atmtab.txt
http://www.engineeringtoolbox.com/ai...ure-d_462.html

Whatever I tried, the results in the Intake manifold, after the SC, were actually worse then directly after the turbo.
Maybe I'm reading wrong though.

I didn't have a chance to test this calculator (typing as I am on my way out), but out of the blue I will say that it isn't this simple. You need to take into account various stuff like difference in the pressure affecting compressors efficiency, various thermodynamic & hydrodynamic laws, etc.

Are the some formulas written that were used in the calc?

Very interesting find, none the less!

[koivis]

I did not say that a normal turbocharged R-2800 or any similar engine would be a turbo-compound engine. I just meant to say that no matter what extra components are added around the engine (including turbos and turbo-compound turbines), it almost always still has a normal, integral, crankshaft driven supercharger.

[koivis]

To confuse myself I and others even more, I present you the ultimate in piston engine technology, actually the most powerful piston engine to have ever powered an aircraft:

Dobrynin VD-4K

I kinda feel sorry for air when it faces this 24-cylinder, six-bank, four-row, 59,5 liter monster, as it has to go through a most confusing route:

Air from intake goes to turbo, turbo blows air into a two-stage, variable geometry supercharger, air goes to cylinders (I assume it had direct injection). Exhaust gases go trough three "blowdown" turbines between the cylinder banks (one for each 8 cylinders = 2 banks), then continues towards the back to go turn the aforementioned turbosupercharger. Probably, after this point, the exhaust gases don't have anything more to give...

The blowdown turbines are mechanically connected to crankshaft, in this case adding some 700 free horsepower. Of course, there is also the two-stage supercharger, and all this most likely needs whole lotta intercooling and other extra piping. I could draw a picture of that, but it's late, and I think that would take some time.

Sources:
http://en.wikipedia.org/wiki/Dobrynin_VD-4K
http://de.wikipedia.org/wiki/Dobrynin_VD-4K

I have a few wonderful books, "TDevelopment of Piston Aero Engines" and "World Encyclopedia of Aero Engines", both by Bill Gunston. These explain the engine and one of them might even have a picture of it. I don't have access to my library at the moment, so the third source is my memory.

Off topic it is, could you pls forgive me...

[T}{OR]

Originally Posted by koivis

Air from intake goes to turbo, turbo blows air into a two-stage, variable geometry supercharger, air goes to cylinders (I assume it had direct injection). Exhaust gases go trough three "blowdown" turbines between the cylinder banks (one for each 8 cylinders = 2 banks), then continues towards the back to go turn the aforementioned turbosupercharger. Probably, after this point, the exhaust gases don't have anything more to give...

The blowdown turbines are mechanically connected to crankshaft, in this case adding some 700 free horsepower. Of course, there is also the two-stage supercharger, and all this most likely needs whole lotta intercooling and other extra piping. I could draw a picture of that, but it's late, and I think that would take some time.

The reason for "added" complexity:

http://en.wikipedia.org/wiki/Turbo-compound_engine

It was realized that in many cases the power produced by the simple turbine was approaching that of the enormously complex and maintenance-intensive piston engine to which it was attached. As a result, turbo-compound aero engines were soon supplanted by turboprop and turbojet engines.