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View Full Version : Turbosupercharging vs. Supercharging



ForkTailedDevil
11-27-2004, 10:50 PM
What is the difference and how are they different say for example from my own turbocharged automobile. I thought turbo-supercharging was the same as a turbo in a car but I have heard otherwise.

xTHRUDx
11-27-2004, 11:01 PM
i always thought that normaly aspirated engines vs turbo vs supercharged engines was how the air was crammed into the engine.

turbo = exhaust driven method to cram air in.
super charged = belt/chain driven method to cram air in.

i could be wrong

Simjock
11-27-2004, 11:39 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by xTHRUDx:
i always thought that normaly aspirated engines vs turbo vs supercharged engines was how the air was crammed into the engine.

turbo = exhaust driven method to cram air in.
super charged = belt/chain driven method to cram air in.

i could be wrong <HR></BLOCKQUOTE>

You are exactly correct.

Tully__
11-27-2004, 11:53 PM
Go here (http://www.avweb.com/news/columns/182146-1.html) and read the articles "Those fire breathing turbos" parts 1 through 6. (#'s 31 - 36 in the series I believe). There are links in the engine related panel on the right side to make them easier to find.

chris455
11-27-2004, 11:55 PM
Superchargers are mechanically driven (belts or gears) "pumps" that force air into the intake manifold of an engine. More air = more power.
(simplified).
Turbochargers use the hot exhaust gas from the engine to turn a turbine that introduces more air into the engine. The net result is the same, more air allowing greater power from an engine of a given displacement.
Some planes in WWII had poweplants that were referred to as turbosupercharged or turbocompounded. These engines had both mechanical and exhaust driven components that greatly increased their power output at altitude. An example of this is the mighty Republic P-47 Thunderbolt featuring the Pratt & Whitney R2800 double-wasp engine coupled with the GE C-23 turbosupercharger delivering 2300 hp at WEP.

k5054
11-28-2004, 03:45 AM
Turbos in the 1940s were pretty hard to make, you needed high-temp alloys. The first turbo-boosted a/c flew in 1919, AFAIK, but the first in service was probably the B-17.

In WW2 I can count eight turbo-boosted aircraft which flew combat missions. Seven were USAAF types. Three were fighters, and this is where the problem came in, fitting a turbo in a WW2 fighter was hard. The airframe had to be designed round it, and this reduced the benefit, or it could be tacked on and therefore not be a good installation.
There are many trade-offs between a turbo and a good mechanical supercharger. Posibly you could say a turbo might just be superior in a long-range high-alt fighter. In a bomber it probably comes out better, all things considered, all for long range and high cruising alt.

Any of you avhist buffs care to produce the list of 8 turbo planes I'm thinking of? Or maybe you know better?

1.JaVA_Razer
11-28-2004, 04:48 AM
If you have a supercharger nad you floor it you'll rocket ahead immediatly because you're belt driven. So you'll pull up VERY fast.

Now with a turbocharger you'll floor it, go forward and 2 or 3 seconds later you'll skyrocket forward faster then the supercharger. It's because the tubocharger needs time to rev up.
Superchargers= fast acceleration but you don't go as fast as with a turbocharger which will give a delay but you'll get much higher speeds.

The best thing is to use'm both.

skabbe
11-28-2004, 06:16 AM
but the supercharger take power to give power, and turbos just give power, superchargers are more eazy to use because it give power all the time in a nice smooth way, turbos is a bit tricky

Taylortony
11-28-2004, 09:04 AM
Turbosupercharging is just a fancy name for a turbo as opposed to a supercharger, turbos you get something for nothing but get lag..... bit like FB http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif A supercharger takes power to produce power but weighs a hell of a lot more, although does not suffer from lag due to being instantaneuos, it also copes better with altitude.

SkyChimp
11-28-2004, 09:12 AM
Turbosuperchargers and mechanical superchargers both sap engine power, but in different ways.

AFAIK, The engine eqipped with a turbo loses power due to exhaust back-pressure, though not as much power as a engine with a mechanical supercharger, which loses power due to the power needed to run the geared supercharger.

The turbo also takes exhaust to run the turbine, which could otherwise be used for exhaust thrust. Exhaust thrust from an engine with a mechanical supercharger could provide a couple hundered pounds of thrust, IIRC.

Turbosuperchargers were generally bigger and bulkier than mechanical superchargers. Both are just excess weight down low. In the American experience, I think it was generally considered that the mechanical supercharger was good for lower to medium altitudes, but the turbo was better for high altitide.

diomedes33
11-28-2004, 11:40 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by skabbe:
but the supercharger take power to give power, and turbos just give power, superchargers are more eazy to use because it give power all the time in a nice smooth way, turbos is a bit tricky <HR></BLOCKQUOTE>

Nothings for free, the engine still has to work to push the exhaust through the turbine.

1st Law of Thermodynamics: You can't win
2nd Law of Theromdynamics: You can't break even

Turbocharger may dissipate less energy than a Supercharger (I don't know), but it still takes power from the engine.

k5054
11-28-2004, 12:04 PM
Something like two thirds of the energy in the fuel goes out in the exhaust. It doesn't break any law of thermodynamics to use a little of that energy to turn a turbine. The effect of exhaust back pressure is minimal, in fact the GE turbo would be the same to the engine as running at sea level atmospheric pressure, by design. Later on they started to overboost the turbo a little more than that. Of course to use the exhaust energy DOES cause it to be unavailable for the not-so-vital task of heating up the atmosphere until a little later in the cycle.

Taylortony
11-28-2004, 12:39 PM
If you want to squeeze a little more power out of it, some of the big radials as on the connie actually used to squirt fuel into the exhaust as the end like a mini reheat system to burn the remaining oxygen and produce thrust from the exhaust system

Korolov
11-28-2004, 03:22 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by k5054:
Any of you avhist buffs care to produce the list of 8 turbo planes I'm thinking of? Or maybe you know better? <HR></BLOCKQUOTE>

P-38, P-47, B-17, B-24 and the B-29 are all I can think of. I can't even remember if the B-29 had turbos.

pourshot
11-28-2004, 03:51 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by 1.JaVA_Razer:
If you have a supercharger nad you floor it you'll rocket ahead immediatly because you're belt driven. So you'll pull up VERY fast. <HR></BLOCKQUOTE>

Correct.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Now with a turbocharger you'll floor it, go forward and 2 or 3 seconds later you'll skyrocket forward faster then the supercharger. It's because the tubocharger needs time to rev up. <HR></BLOCKQUOTE>

Correct, however it wont happen if your revs are already elevated slightly, for example if your set you engine controls for a fast cruise.Even so I dont think the lag would be very much with the compound supercharging used on aero engines.


<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Superchargers= fast acceleration but you don't go as fast as with a turbocharger which will give a delay but you'll get much higher speeds. <HR></BLOCKQUOTE>

Incorrect as in the end it comes down to how much air (volume) the gear driven supercharger/turbo supercharger can pump and at what boost level.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> The best thing is to use'm both <HR></BLOCKQUOTE>

Correct


This topic came up some time ago and it did show that supercharging and turbo supercharging where interchangable in the aero industry as terms used to discribe forced induction.Many mechanical blowers are listed as turbin superchargers probably becuase of the use of impellers as apposed to rotating screws.

WTE_Galway
11-28-2004, 04:12 PM
a minor point

in aircraft the supercharger (turbo or otherwise) is generally not there to provide extra power

its purpose is to compensate for the loss of pressure at altitude so the engine can still provide maximum sea level power even at high altitude

diomedes33
11-28-2004, 04:34 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by k5054:
Something like two thirds of the energy in the fuel goes out in the exhaust. It doesn't break any law of thermodynamics to use a little of that energy to turn a turbine. The effect of exhaust back pressure is minimal, in fact the GE turbo would be the same to the engine as running at sea level atmospheric pressure, by design. Later on they started to overboost the turbo a little more than that. Of course to use the exhaust energy DOES cause it to be unavailable for the not-so-vital task of heating up the atmosphere until a little later in the cycle. <HR></BLOCKQUOTE>

I'm not saying it broke any laws, I was using the thermo laws to back up what I said; Nothing's for free.

@WTE_Galway you answered my next question thanks.

ForkTailedDevil
11-28-2004, 08:22 PM
Wow I am glad to see so many good responses. I know quite a bit about turbocharging espacially on cars so I was curious to know the difference. Another question what kind of superchargers are on most WW2 aircraft are they centrifugal (spelling?) or roots style? Also does a belt spin the blower like on a car if so how can you does it work in the engine for example when you change blower speeds?

pourshot
11-28-2004, 10:19 PM
Here is a great site to learn about aero engines enjoy engine history (http://www.enginehistory.org/)

VMF513_Viper
11-28-2004, 11:00 PM
Hi Just my 2 cents,

A good article on How Superchargers and turbochargers is on il2flying.com

Located in Viper's House of Pain

http://www.il2flying.com

Viper

effte
11-29-2004, 05:31 AM
Turbines don€t run off heat, they run off pressure. If you have a turbine in the exhaust, you get an increased pressure in the exhaust manifold. This means more work for the engine to get rid of the exhaust gases €" which means less power out at the shaft.

While chargers did compensate nicely for the effects of altitude, they also made sure that the engines could provide massive amounts of power per cubic inch down low, a lot more than what could have been achieved without forced induction. Think about it. You had a MAP way above SL ambient pressure. This means a lot more fuel-air mixture in the combustion chambers than at one bar!

If chargers were dead weight down low, we wouldn€t have them in cars would we?

On a sidenote, I suspect most of the losses associated with turbocharging are found in the ducting required. Anyone got the facts?

Cheers,
Fred

Abbuzze
11-29-2004, 06:46 AM
A supercharger is "eating up" upto 30% of the plus power resulting through his work. Hope I remember the correct number.
The turbocharger has the advantage that it is driven by the exhaust and has no mechanical connection, which results a loose of power...

skabbe
11-29-2004, 07:43 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by diomedes33:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by k5054:
Something like two thirds of the energy in the fuel goes out in the exhaust. It doesn't break any law of thermodynamics to use a little of that energy to turn a turbine. The effect of exhaust back pressure is minimal, in fact the GE turbo would be the same to the engine as running at sea level atmospheric pressure, by design. Later on they started to overboost the turbo a little more than that. Of course to use the exhaust energy DOES cause it to be unavailable for the not-so-vital task of heating up the atmosphere until a little later in the cycle. <HR></BLOCKQUOTE>

I'm not saying it broke any laws, I was using the thermo laws to back up what I said; Nothing's for free.

@WTE_Galway you answered my next question thanks. <HR></BLOCKQUOTE>


its for free, you dont even have to count the loss, and when it spinns it will suck the exhaust out of the enginen, almost.... ones they tested to make a small 2 liters enginen with 800hp, they used supercharger, and just the charger took 75 hp from the effect. both turbos and supercharger are both needed...

Von-Wand
11-29-2004, 09:02 AM
Hello All,
Just a quick one,

The supercharger supplies a constant pressure of air (ie 1 bar) wether at idle or running flat out, the pressure dosnt alter only the volume (amount) changes.The only limiting factor is the speed it can turn at, which is why some aircraft have two speed superchargers, and the size of the throttle housing which restricts the air flow.

The turbocharger has no pressure at idle and supplies very little volume. As the turbo spins up to speed (driven by exhaust gases from the engine) both the pressure and the volume of air rise very quickly. Again the only restriction with a turbo is the size of the throttle.

With a supercharger there is no lag as it is already suppling pressurised air even at idle( instant throttle responce). The lag with a turbo is the time it takes to spin up to speed. Also with a mechanically driven device you have the option to turn it off (to save fuel) via a magnetic coupling. Both are as good as each other but in different ways.It must be noted, that on alot of German aicraft a G-charger was used, a sort of mechanically driven turbocharger!

I hope this helps abit!



"Meine Ehre Heisst Treue"

effte
11-29-2004, 11:39 AM
skabbe, Abuzze,
it was explained above that the loss when using a supercharger is through exhaust backpressure. The engine has to work to push the exhaust gases through the turbine.

To say that a turbine will suck the air, well, I€m sorry but that is just unbelievable. You really need to go read up on turbines as you clearly don€t have the slightest idea about how they work! I may sound harsh, but if you are going to make statements in public forums where you claim to know how things work it is your responsibility to have that knowledge first€¦ or expect to be told so.



A supercharger does not run at a constant speed. The speed will change with gear and engine RPM. The pressure increase over the blower will change with RPM. Other than that, good explanation.

k5054
11-29-2004, 01:37 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
it was explained above that the loss when using a supercharger is through exhaust backpressure. The engine has to work to push the exhaust gases through the turbine. <HR></BLOCKQUOTE>

Here's a quote from Gunston about the effect of back pressure..

"The piston finishes its exhaust stroke with a pressure remaining in the cylinder of about 85 psi. Thus, when the exhaust valve is opened, the pressure ratio across it is at least 6, far above the critical value. Consequently the pressure downstream has no effect on the rate at which the gas leaves the cylinder. At BDC the exhaust valve is already partially open, and before the engine has to expend work in positively pumping out exhaust against back pressure more than 75% has already escaped. Thus, three quarters of the turbo gas is obtained at no cost in crankshaft power, only the remaining quarter having to be pumped out. The net result is that the turbine HP is four to five times as great as the power taken for mthe engine in pumping against back pressure. Even with a turbine efficiency as poor as 65% the turbo still recovers two to three times the lost crankshaft power."

That ought to go some way to show what effect back pressure has.

To clear up some car comparisons, in WW2 aircraft supercharger, there are no belt drives, only gears and sometimes hydraulic coupling. There is no supercharger which can be disengaged, although the R2800 had a neutral gear for the first stage supe, not the second.
All compressors are centrifugal, no Roots or other blowers. RPM was in the 20,000 range.
For a centrifugal compressor, mechanical or turbo, the output pressure varies with the square of RPM, the power used with the cube of RPM.

diomedes33
11-29-2004, 03:14 PM
@k5054

To clarify somethings.

The turbo does take away from the engine. However, with the higher compression ratios generated by it, you gain much more power then was used to turn the turbine?

@skabbe
Explain how it can be for free?

This is the way I understand it.

Take an engine without a turbocharger and straight pipes.
inlet pressure = outlet pressure
Only source of power is the explosion of gas/air mixture
The engine is using some of this power to turn a shaft, some of it to blow the exhaust out the pipes and some is lost due to inefficeny.

Take an engine with a turbocharger during lag (turbine is still spooling up)
Now the engine is using power to turn the shaft, blow the exhaust through the pipes and turn the turbine. More energy is lost to inefficeny there is no way the turbo is perfectly efficent. This will take more power to run then it would for straight pipes.

When the turbocharger is running it effectively places a compressor inbetween the inlet and engine. This increases the compression which increases the power generated by the explosion. You still have to push the exhaust out of the engine through the turbine and now the turbine is spinning the compressor in the intake. Power that is generated is lost at all these points.

Its not for free you're helping the engine make a bigger boom.

I have a car with a turbocharger in it. It has pretty slow acceleration between 1000 - 3000 rpm, slower than it would without it. As soon as I hear those impellors wind up, it takes off like a bat out of hell.