-Jehuty+Jan 10, 2005 - 11:08 AM

Ok So if I stick my turbo in an oven I'm going to be making boost? Heat being the main factor in making the turbo spin doesn't make any sense.

No, heat still IS the main factor to turbo spool. Without heat air expanding, you would never spool up or suck in air; because it'd always be at the same pressure. You'd suck in cool air, and just as much cool air would "push" the turbine. it doesn't work.

-WannabeGT4+Jan 10, 2005 - 12:33 PM


Haha, not quite! But if you where to dissapate heat from your pressurized exaust gasses by say... running them down the length of your car's underbody where cold air rushes by... they would remain pressurized, but not have as much of the energy to expand, dissapate, and spin the turbine as would hot gasses.

Of course, according to the Ideal Gas Law, we could be arguing semantics here, as there is a direct relation between pressure and heat. However that does not make my initial statement that turbines are driven by heat any less true. Nor does it change the fact that turbine performance would suffer if the exhausts gasses where cooled before reaching the turbine.

-Jehuty+Jan 10, 2005 - 5:49 PM

Your arguments are true, but how you arrived there is false.

-shid+Jan 10, 2005 - 12:51 PM

If you are reffering to the part about the outlets of the turbo manifold, then it's down to heat and pressure not being completly interchangable in that part of the turbo system. However, different manifold/turbine housings have been designed to emphasize either pressure, heat, or both. Is that the part that could be considered false or am I lost here?

A turbo works almost exactly like a gas turbine engine (Link: http://travel.howstuffworks.com/turbine.htm )

and here's how turbochargers work:

http://auto.howstuffworks.com/turbo.htm

because heated gases take up more space than cool gases; you are correct in saying without heat, the gasses would cool and take up less space- less pressure. However, you are incorrect in saying that the air does not move the turbine like a waterwheel- it is exactly like that.

-shid+Jan 10, 2005 - 1:08 PM


Oh, I see. I was just trying to illustrate the difference between the way many people think a turbine works and the way it acutally does. That is, the picture many (if not most) people get in their head is that of the exhaust gasses "blowing" the turbine wheel. Hmmm, even that description can be ambiguous. Anyhow, yeah it's hard to clearly converse about. But I think we're on the same page. I hope I didn't make it more confusing than it needed to be by trying to explain myself.

but exhaust gases DO blow the wheel.

-shid+Jan 10, 2005 - 12:26 PM

LOL That's what I was trying to say.

-Jehuty+Jan 10, 2005 - 1:18 PM

I'm going to run out of ways to say this. I'm trying to point out the distiction between flowing gasses simply pushing the turbine around, and energy (heat) being reclaimed by the turbine wheel. And while you could say that flowing gasses do indeed simply push the turbine around, I think it's worth making the distinction.

And after all this, bleading the heat from the exhaust before it reaches the turbine still hurts the performance of the turbine. Re-interpretation of my admittedly gray-area language doesn't change that.

-Jehuty+Jan 10, 2005 - 9:35 PM

What you don't seem to realize is that a turbine would spin just fine even if there was no heat energy. Energy is energy; and the turbine changes that form of energy. Thats all. Heat has no special part in driving the turbine any more than blowing on a uhh.. one of those hand head windmill spinner things does.

You're getting confused because you believe that the transfer of energy is straight from the hot air (heat energy) to kinetic energy in the turbine; thats not true. The heat energy makes NO direct thermodynamic transfer to the turbine wheels.

here's what it comes down to; in a supermarket there is a revolving door. People want to get into the supermarket so they cram in together; and the revolving door takes lik 4 people at a time.

Inside the store, they get fat because they open and eat all the candybars, and they only leave one at a time- but they're still the ones pushing the door.



Inside the engine, close proximity air molecules are combusted and heated so that they take up more space. This explosive force directly drives the turbine; heat has no direct relation to it.

yes, it still would be a bad idea to give the molecules a chance to cool down and group together; but thats not the same thing.

ohhh someone seems to be a physics major...

Yes the main energy source of a turbo is to have air spinning the turbine. But the extreme hot gasses also help the turbo increase its efficency.

simply..

20 gallons of 5psi cold air will make a turbo put out 3 units of energy..
but..
20 gallons of 5psi hot air ( like car exhaust temp) will make 3.1 units of energy.

why would there be more energy put out? Well, we all know hot air likes to expand. If the turbo design manages to catch this expanding energy, the more energy it can produce.

Simple -

Exhaust gas blows on the turbine making it spin

Hot and Pressurized air makes the turbine spin faster.

And since you don’t seem to grasp the idea that your exhaust pipe really doesn't dissipate heat like you think, I’ll say it again. The spool time between the two is roughly the same. You’re arguing that this is a bad design. Sometimes it’s the only design. Hell the new LF-A has the radiators in the back! Sometimes odd designs must come into play to make things to work. The difference between to two is small, and also, maybe the difference is made up because all that heat you talk of is in the back far away from the intake. >>

-Ti