[merve_extreme]

Originally Posted by DRC

certainly the turbos must use some power to produce some.. Can you elighten how much of a power does a turbo use..

turbo does not use the engines power.it uses the redudant or waste power in the exaust gases of the engine to run itself.

I was actually planning to put in an electrical turbo fan just to experiment.. So I can have more control.

this is what is called as the supercharger.it uses the engines power to run itself(hence it is fitted on the crankshaft).

Both turbo and superchargers work on the same principal and do the same work,only diffrence is that since supercharger runs on the engine it produces boost continously till the engine is running whereas a trubocharger produces boost only when the pressure of exaust gases is strong enough to run the turbocharger which happen at a higher rpm say 1500-2000RPM onwards(hence the associated turbolag).

[DRC]

MX,
that defies the LCE. Where does the energy to spin the turbo come from.. From exhaust! Now if any one goes for a hypothetical free flow, which means, 0 back pressure, then, the turbo can not use the energy from exhaust. In any case that is the load on the prime mover.

My 2 cents of learning in school

[merve_extreme]

the turbofan is rotated by the gases comming out of the engine exaust outlet(before connection to the silencer and exaust system of the vehicle).it is like if we hold a fan and blow air into it,the fan starts spinning due to the flow of air through it.the flow pressure is what i am talking about.the higher the speed of the exaust gases the faster will the turbofan rotate and this will lead to increased air suction.

IMO even if we disconnect the silencer unit the turbo will work just fine or maybe even better since the exaust gases will flow unrestricted and this will increase the speed of the gases(i:e it will increase the pressure,genetrated by the exaust gases while rotating the turbo's fan).

[merve_extreme]

this is the diagram i have drawn.i think u can very well see how it works.diagram is not exact.

[DRC]

MX, Are we missing the whole point here...
I know that the exhaust gases will still have a little bit of energy let in them which the turbo tries to make use.
Now, Let's try to understand the free flow working.. They eliminate /reduce teh back pressure generated by the exhaust system to let the engine generate more power. If a complete free flow is used and a turbo is added to it, then the very presence of turbo will reduce teh effect of the free flow because the turbo will cause some back pressure. And this back pressure is reflected on teh Engine. This is exactly the energy being used by the turbo to spin (though wasteful in practical cars).

The question I am trying to find the answer for...If I had to run the same turbo with out using any of the engine power, neither crank nor exhaust nor anything else that taps on teh engine, say I will connect a seperate engine powered by a seperate fuel tank, or a electric motor powered by 230V AC etccc., then how powerful a prime mover should I use?

Hope I am clear, else we can ask more question to each other to get some clarity...

[merve_extreme]

OK now i got to know what u wanted to say.

see in my diagram if u see the turbine design then the airfows from the side and exits from the front.the air thus loses very less momentum.certainly it will cause some back pressure to build up,but i dont think it will affect the working of the free flow much.

ur concept of fitting a electric fan is an energy effecient idea,but it wont work for the turbo.the turbine of the turbocharger spins at about 30 times the speed of the engine.so if ur running at 5000rpm then the turbine will rotate at 150000rpm(that why it gets so hot).this high speed is needed to compress the air to pressures of 10psi +.so even if u fit a electric fan it wont work since u cannot achive enough compression of the air for the turbo system to be effective since the electric motor is not going to spin faster than 1500rpm.

fitting another engine is not a good idea since ur going to spend more energy than u can generate and u will also waste a lot of fuel for small increase in power.another difficulty will be in maintaing the rpm of the turbine acc to the speed of the engine.

and then even if u got it to work somehow,i cannot tell how reliable it is going to be.hope u got what i wanted to say.

[Boom Shiva]

If you're really power obsessed then go for a twin turbo setup or something like that.

[ananthkamath]

Originally Posted by merve_extreme

see in my diagram if u see the turbine design then the airfows from the side and exits from the front.the air thus loses very less momentum.

You are absolutely right. A turbine is a device meant to convert dynamic pressure head to static pressure head. In simple terms this means that the velocity of the gases is gained when they are used to spin a turbine. See this diagram:



In a turbine, the blades are such that the area of cross-section keeps decreasing, so that the pressure decreases. So the backpressure is positive and equal to (P2 - P1).

But due to the volute casing of the turbine, which has a smaller inlet than exit, some amount of this backpressure is reduced. So the NET BACKPRESSURE is less than (P2 - P1).

In a compressor, the opposite happens and so the backpressure is negative.

Take a look at the turbine and compressor section from a Garrett turbo. The aluminum one is the compressor section. You will see what I am talking about:




What all this means is that having a turbo is effectively free power. Yes, a turbo is the classic advocate of a free lunch!

Ananth

[DRC]

let me put my question, which every one has understood, in "i mean business" way..
If an engine is developing 100 bhp and with a turbo develops 130 bhp, how much bhp are needed to spin the turbo, irrespective of where the enrgy come from (even if a paid lunch way). Spinning it 150krpm to 10psi does take a sizable energy!

Examples of using an electric motor or a engine are only hypothetical and for the arguement sake only!

[ananthkamath]

Originally Posted by DRC

let me put my question, which every one has understood, in "i mean business" way..
If an engine is developing 100 bhp and with a turbo develops 130 bhp, how much bhp are needed to spin the turbo, irrespective of where the enrgy come from (even if a paid lunch way). Spinning it 150krpm to 10psi does take a sizable energy!

Examples of using an electric motor or a engine are only hypothetical and for the arguement sake only!

Well then let me put my answer, which all but you have understood, in a "I am stupid" way: Nobody does those calcs. All they see is how much NET power they are getting by running a turbo at x psi. If you still don't get it, ask the kind people at AVL, Austria. Chances are, they will tell you the same thing.
And if it helps, let me tell you that your battery will be out of juice before you even start to make boost with your electric supercharger.

[ananthkamath]

Sorry if the previous post sounded harsh. Saw your original question. I suggest you read this before you try anything:


http://digest.net/bmw/archive/v7/msg08818.html

http://digest.net/bmw/archive/v7/msg09047.html

http://digest.net/bmw/archive/v7/msg09049.html

And also, supposed dyno gains from the "original" electric supercharger, the e-RAM:

http://www.electricsupercharger.com/dyno.shtml

[DRC]

thanks ananth, for the useful links
I think this way it works (language)..

Now I understand, compressing that amount of air to 1.7psi needs about 1bhp, and doing the same, if the equations are linear, need about 8-9 bhp ( so much drawn from the engine, though wasteful). No doubt it will drain the battery!!

Now , I have to think other ways, How about scoops?

[DRC]

9 bhp going through the exhaust pipe!!!! what a waste man

[ananthkamath]

With scoops you may get 1 psi at 140 kph

[merve_extreme]

Scoops have only one primary function and that is to let cool air enter the engine bay for a cold air intake and the other reason is Style.