Requesting information about compressors (ie turbo or supercharger) [Archive]

TangoR34

30th November 2007, 21:01

Hi all, I am doing a physics coursework finding information about how turbo and supercharger works and arguing which is better. I would really appreciate some detailed information without wikipedia waffle. any useful links would be great because google just come up with people selling stuff that kind of bu**s**t.
BTW is turbo actually more efficient than a supercharger like wikipedia says?

Daniel

30th November 2007, 23:08

A turbocharger is driven by "waste" gases. A supercharger is powered by the engine. You do the maths :)

Magnus

1st December 2007, 08:27

This is a huge area in itself. I wil come back to you later, if no one else gets to it first.
However: which is better? Depends on application. SC is better at low revs, since you have no exhaustflow to rotate the turbine fast enough at low revs. SC is driven by a belt or a chain. Volvo Penta often has both SC and ord. charger, with the turbo kicking in at abt 2500 rev.
Mind you: wastegate, adiabatic grade of efficience, the weight of the turbine (heavy one causing great lag), adjustable turbineblades, the necessity of cooling with gas/water, the necessity of lower comp., and more...

Magnus

1st December 2007, 08:52

Wki is actually good enough in this area. Also look here: http://en.wikipedia.org/wiki/Heat_capacity_ratio abt adiabatic rates and so on.
Regarding the efficiency hey are quite right, but as always it depends...
Please note that there are quite a few different kind of sc aswell. Btw: Roots blower+hemi is a nice combo!
Feel free to ask if you like, but my suggestion is you start out with wiki.
The links at the end of the article is also rather good!

TangoR34

1st December 2007, 22:42

ChrisS

2nd December 2007, 00:03

why can supercharger cannot boost better at high revs than a turbo then? I'm sure that the engine will spin quick at some point and drive the SC quicker. is there anyway for a SC to be more efficient than a turbo?

because a supercharger is powered by the engine it takes power away from the engine to work. superchargers can use up to 20% of the engine horsepower

these may be useful
http://auto.howstuffworks.com/turbo.htm
http://auto.howstuffworks.com/supercharger.htm

Daniel

2nd December 2007, 14:34

why can supercharger cannot boost better at high revs than a turbo then? I'm sure that the engine will spin quick at some point and drive the SC quicker. is there anyway for a SC to be more efficient than a turbo?
Because the more revs the more gases and the more power the turbo gives. The turbo isn't engine driven so therefore doesn't use any power. A supercharger takes LOTS of power from an engine and so as it revs higher the gains are somewhat offset by the huge loss in power. But it all depends what you want. If you want power from the moment you put the car in gear you get a supercharger. If you're happy to wait a little while for the power you get a turbo.

Advancements like anti-lag and variable geometry turbo's have somewhat lessened the gap between low end power that a turbo gives over a supercharger.

airshifter

2nd December 2007, 22:32

Kneeslider

3rd December 2007, 01:18

Hi there,

When you are trying to evaluate the pros and cons of supercharging versus turbocharging, as several other correspondants have noted, it all depends.

To say that there is no loss associated with bolting a turbocharger to an engine is folly. The engine breathes through it's exhaust pipe, and if you were to bung this up with a turbocharger, then of course there would be a restriction, which would have a detrimental effect on efficiency. If you look at what you mean by efficiency, then it might be better to start with something simple, like a Stirling engine. Have a look on the internet about them, and you will probably find lots of Physics related things which will lead you to know more about energy in, vs energy out, work, energy and power, and how you quantify them, if you get a long way, then you will be interested by the concept of Entropy.

Just because turbo and superchargers are everyday things, doesn't make them simple to understand.

In practical terms, if you take an engine and are looking to get the 'ultimate' output from it, then that all depends upon how much boost pressure it will tolerate before trying to reduce itself back to its molecular origins!

Daniel

3rd December 2007, 01:35

I would agree with most of the above by Daniel, but turbos do create pumping losses, and are also somewhat affected by heat rather than just sheer flow. Many turbos will generate very little boost until they are under load for that very reason.

The gaps are getting smaller for both turbos working better at low revs, and blowers being much more efficient. Many of the newer centrifugal blowers have much reduced parasitic losses, and still over great low end boost levels.

Both are subject to areas of higher or lower efficiency based on the trims of the impeller and/or rotors.
Well yes you do get turbo lag and there is "loss" but the loss from a turbo is far less than that of a supercharger and is more than made up for by the power gain :) So you might lose efficiency (as in fuel economy) but it's only low RPM ranges where you lose power. Problem is with a supercharger it can use a huuuge chunk of power at the top end plus it's not as efficient as a turbo as it's not using "waste" energy.

rah

3rd December 2007, 03:02

Just a few things of interest.

There is an electric powered supercharger. Not sure on the performance of it though but it does sound interesting.

Not all supercharges work all of the time. Some kick in at specific revs, some kick in at full throttle.

Kneeslider

3rd December 2007, 13:42

I don't know if Daniel knows what he is talking about....

So I guess that we need to go back to first principles....

Daniel

3rd December 2007, 14:09

I don't know if Daniel knows what he is talking about....

So I guess that we need to go back to first principles....
Explain.....

Kneeslider

3rd December 2007, 15:01

Well I just want to say that the original question as posed by TangoR34 is rather ambiguous. When you say best, what do you mean? If you mean which is capable of producing the most power, or which is the most efficient, in terms of energy in vs energy out, because they are very different questions!

And Daniel, the loss of efficiency (quantity of power consumed by a supercharger, or a turbo) has nothing to do with the concept of "Turbo lag" :p :

Daniel

3rd December 2007, 15:23

Yes.

I didn't say it did ;) I said you get turbo lag and pumping losses :) Although I did kind of insinuate it later on in my post unintentionally :p I meant "lose" power as in the net loss a turbocharged engine would have over a well tuned NA engine at low RPM. Apologies for the ambiguity there :) For the purposes of the discussion I'll use efficiency and power from now on :up:

airshifter

3rd December 2007, 19:00

I have to agree with Kneeslider, that the differences and technical issues are far greater than most sterotypes suggest.

On many modern applications, turbo lag is a thing of the past unless the turbo is a trim designed for high RPM use primarily. Likewise, some of the new blowers are very efficient. Both produce power well above the same naturally aspirated engine at virtually all RPM.

Even within a certain type of application, variations in design can make huge differences. I have an excellent article on the Eaton vs Autorotor superchargers, and the differences are immense.

TangoR34

4th December 2007, 08:40

Then can I ask another thing. Does a SC produce far better power or boost (because they are normally used on exotics) than a turbo, regardless to efficiency and powerloss on the way?

Daniel

4th December 2007, 10:13

Then can I ask another thing. Does a SC produce far better power or boost (because they are normally used on exotics) than a turbo, regardless to efficiency and powerloss on the way?
Not sure why you say superchargers are more often found on "exotics"?

Such as
Ferrari F40
911 Turbo and GT2
Bugatti Verywrong

and so on.

All cars which use Turbochargers.

Kneeslider

4th December 2007, 10:57

Then can I ask another thing. Does a SC produce far better power or boost (because they are normally used on exotics) than a turbo, regardless to efficiency and powerloss on the way?

A supercharger, or a turbocharger can produce however much boost you want it to. Normally, the quantity of power you want to produce is proportional to the boost pressure. Therefore, a reciporicating engine with a turbo or a supercharger can produce however much power you want it to.

The limiting factor is how much pressure you can stuff into the cylinder before it starts to detonate or 'pink', which is what happens when the mixture in the cylinder ignites spontaneously BEFORE the spark occurrs, like in a diesel engine, but at a point considerably in advance of the 'normal' ignition timing point of the engine (typically 8° Before Top Dead Centre at idle, and around 38° BTDC at a few thousand revs) Engines are timed to fire BTDC so that by the time all of the mixture is combusting, and expanding at it's optimal rate, then engine is at a point after Top Dead Centre, on the 'power' stroke. The burning process of the mixture occurrs at the same rate regardless of the speed of the engine, so at higher engine rpms, you can use more advance (to a point)

You didn't say what sort of level of info you require for your physics coursework, is it GCSE, A level, or degree. It would help to know, so I don't assume you know more, (or less!) than you do! :D

Daniel

4th December 2007, 13:13

A supercharger, or a turbocharger can produce however much boost you want it to. Normally, the quantity of power you want to produce is proportional to the boost pressure. Therefore, a reciporicating engine with a turbo or a supercharger can produce however much power you want it to.

Can't be bothered reading the rest of your post.

I'm off to turn the boost up on my 406 :D

Boom! :arrows: :laugh:

TangoR34

4th December 2007, 14:13

well I'm dloing A level actually and another question is why is turbo still more popular than supercharger? is it because of the cost of installment?

Daniel

4th December 2007, 14:51

well I'm dloing A level actually and another question is why is turbo still more popular than supercharger? is it because of the cost of installment?
Efficiency and net power gain I would say but wait for kneeslider to confirm :p

Azumanga Davo

4th December 2007, 16:50

http://www.competitionplus.com/2005_04/photos/sports_nationals/mike_ashley.jpg

I always know what I prefer... :D

airshifter

4th December 2007, 16:52

well I'm dloing A level actually and another question is why is turbo still more popular than supercharger? is it because of the cost of installment?

In comparison of average cars that a normal person could buy, they are probably very close in popularity. Both accomplish the same basic task, but do so with different variables.

In daily driven cars, reliability and ease of use in cross platforms is important to the designers, not to mention those watching the money. In this respect superchargers might be easier to adapt to various platforms, as changing boost levels is often as simple as changing a pulley that drives it.

By comparison turbos have to be more properly matched to the specifics of an engine, unless you want the ability to adjust boost levels and vent excess boost. This is often done in modified vehicles, but for a large scale production run may not be as cost efficient. Since turbos use exhaust gasses to drive the impeller, they also require a different exhaust manifold. This wouldn't be a large concern to someone building a modified car, but adds up quickly with production costs to a company.

Zico

4th December 2007, 18:00

You may also want to include in your studies engines that are both TC and SC. In Rallying the Lancia Delta S4 had both forms of forced induction, the supercharger to increase the torque/power at the lower rev ranges until the turbo spooled up fast enough to take over improving drivability by reducing turbo lag. Its explained in more detail here..
http://homepage.virgin.net/shalco.com/lancia_S4.htm

Volswagon have sucessfully introduced a Supercharged and TurboCharged Diesel engine option to their current line-up, a 1400cc TSI "Twincharger" that has 170ps but has already been shown to be able to achieve 230PS in standard form simply by chipping or remapping the ECU.
It has the best of both worlds and then some.. Ultra efficient, a much broader power band than a typical Turbodiesel.. It revs to over 7000rpm! Very impressive..

http://www.drive.com.au/Editorial/ArticleDetail.aspx?ArticleID=40001

Daniels thread on how Toyota cheated by by-passing the restrictor may also be of interest to you if you haven't seen it.
http://www.rallyforum.com/forums/showthread.php?t=121013&highlight=toyota+cheat

Zico

4th December 2007, 18:19

Then can I ask another thing. Does a SC produce far better power or boost (because they are normally used on exotics) than a turbo, regardless to efficiency and powerloss on the way?

As mentioned earlier, I dont believe thats strictly true that "exotics" usually have superchargers. With modified cars on the other hand, its usually cheaper and easier to supercharge the engine as its a relatively simple modification as opposed to turbocharging an engine which was not designed/built with lower compression figures to accomodate and allow the high boost pressures turbos produce without blowing the engine. So much more work is required to turbocharge than supercharge a former naturally aspirated engine.

well I'm dloing A level actually and another question is why is turbo still more popular than supercharger? is it because of the cost of installment?

What Daniel says AND... Turbo power although having a more spikey delivery is probably considered more tunable, quick easy gains simply by installing larger injectors, a larger intercooler and adjusting boost pressure.

TangoR34

4th December 2007, 20:32

Does a supercharger suffer 'knocking' as well as turbo? Does it have the potential to heat up the air while compressing them?

Daniel

4th December 2007, 20:40

If you compress a gas you heat it up.

TangoR34

5th December 2007, 07:56

then does it need an air cooler like a turbo does?
What other disadvantage does a supercharger have other than taking power from the engine, adding weight to it and make it spend more fuel?

Daniel

5th December 2007, 08:11

then does it need an air cooler like a turbo does?
What other disadvantage does a supercharger have other than taking power from the engine, adding weight to it and make it spend more fuel?
I think if we continue on like this you might as well just post what your project is about and let Kneeslider write it :)

If you provide a link to this thread in your references your teacher isn't going to be impressed! Google is your friend.

Kneeslider

5th December 2007, 08:26

then does it need an air cooler like a turbo does?
What other disadvantage does a supercharger have other than taking power from the engine, adding weight to it and make it spend more fuel?

Those are pretty much the disadvantages. But you could also say that they are the same disadvantages which apply to turbochargers too.

A lot of the time, you don't NEED an intercooler, (if that is what I think that you mean) but using one is desirable to improve volumetric efficiency.

If you think of an engine as a pumping device for pumping an ideal gas (a gas where pressure is proportional to volume at constant temperature) when the super or turbocharger does work on the gas, to compress it, then the temperature goes up, which leads to a loss of volumetric efficiency, cooling the charge gets this back, and the practical upshot is that you have more power at the wheels.

Ta for the compliment Daniel, but I have other things to do, like try to get enough bits together to finish my project hi comp 900ss engine! ;)

airshifter

6th December 2007, 03:35

then does it need an air cooler like a turbo does?
What other disadvantage does a supercharger have other than taking power from the engine, adding weight to it and make it spend more fuel?

Cooling the compressed charge is always helpful, but not really required at lower pressure levels. Different types of compressors will affect heat in different ways. As stated by Kneeslider, cooler air is more dense and improves volumetric efficiency.

The concerns of detonation (knock) as the same with both superchargers and turbochargers. As more air is forced into the cylinders more precise spark and fuel control are needed.

The additional fuel is required to maintain the correct air/fuel ratio of the mixture for proper ignition and burn. Unless the compressor is producing boost, the engine runs as normal.