Right...

It has nothing to do with the movement of air through the turbine, and doesn't spin the turbine. Heat does.

Does heat make windmills turn too?

And besides, without your turbo encabulator nothing would run.

YouTube - ‪Turbo Encabulator‬‏

 

Because cooling exhaust gases, in a straight pipe, slow down as they contract.

Pistons push the exhaust out of the cylinder into the exhaust. Not to mention that the exhaust is still expanding as the exhaust valve opens. So all in all, you get a net "flow" of exhaust gas into the manifold and out into the pipe.

The turbo impedes the flow of exhaust, just like a clogged catalytic converter would. Instead of the pressure acting backwards (backpressure) and impeding the pistons on the exhaust stroke (and in fact it still does with a turbo), that pressure is used to spin the turbo. Pressure acting on the individual vanes in the turbo wheel push that wheel. The higher the boost on the intake side, the more work is required to spin the exhaust side, which means even more backpressure.

Now, OF COURSE heat is essential to all of this, but it's not the driving force. Flow and pressure is. Heat helps keep the volume of the gas up, and pressure in the pipe before the turbo, and the velocity of said gases.

But, theoretically, you COULD engineer a tapered pipe with a certain amount of cooling effect, where you could predict the amount of contraction of the gas versus the narrowing of the pipe, keep the velocity up, and still have the same net effect on the turbo vanes. Matter of fact, I posit that you COULD actually get a more efficient turbo using a smaller wheel, using denser, cooler exhaust gas, and achieve the same effect, coupled with less centrifugal weight of the exhaust turbine wheel might actually yield better spool up time.

It all comes down to the number of molecules, and how fast they impact the vanes of the exhaust wheel. The temperature of said molecules matters not in a direct kinetic-energy effect.

 

Yes, it does. Heat creates the wind, which in turn spins the windmill.

 

Yes, but if the world was all 500* hot... and not changing.. I bet there wouldn't be a lot of wind movement...

 

More energy is expelled.through the exhaust than is actually harnessed into forward motion. . . .this means there is a PHENOMENAL amount of energy passi.g through the turbo. . . . .i.e. heat. Air alone is not spinning the.turbo 200,000+ rpm. . . . .it goes back to the candle/propeller comparison. The candles prob release 1 btu a piece and that spins the prop. There is 70-90,000 btu of thermal energy passing through the turbo. A mere 40 psi of drive pressure cannot provide that kinda energy. . . . . . . . .

 

40 psi of air has a lot of oxygen in it. Next time you light up an acetylene torch, see how much that good old O2 helps it burn. And, add that 40PSI to the intake charge, which is normally 15PSI, so you have a net of 55PSI. Compress that at 12:1, or whatever a PSD uses for static compression, and you have more than three times the "naturally aspirated" dynamic cylinder pressure. With three times the O2, you have three times the power.

It's a "net positive" - the mechanical energy required to pump more O2 into the cylinders is outweighed by the mechanical energy "robbed" from the engine by driving the turbo.

If it only had to do with heat, why does a supercharger work? (see note below) The Detroit Diesel 6-71 blower exists for a reason.

*NOTE: Superchargers add to the rotational weight of the engine. Acceleration is directly effected. Turbos, not so much. They do rob power, but not directly, allowing faster spin up at the crank.

 

Where does all this pressure come from?
No, no, no, no, no, no.

IT IS the driving force.
I will take that bet
It matters greatly.

Go back to PV=nRT

n and R are a constant in this.
If the Volume is a constant (which it isn't - but it doesn't change anywhere near as much as the Pressure), what causes the Pressure to change?I am not sure whether that was intentional, but its a very astute point you make. Energy has entropy too (i.e. quality), if your base point is 500*, then its worthless, but its the temperature differences which provide value to the energy

 

Thats how Turbo Chargers add Power - Super Chargers add power by the same manner, by forcing more air in (and having more fuel delivered).


What we are debating is that a Turbo engine is more thermally efficient.
Myself and '89F2urd (and some others) are contending that they are, and that for the most part Turbo's are driven off energy that in a N/A engine would be wasted in the form of exhaust heat.



So I will come back at you. How does a Gas Turbine engine work?

 

As a few others have said, because of the EPA...



Pressure does spin the turbo, but the heat increases the pressure.

The idea on the 6.7L having the inverted manifold system is so that the heat will reach the turbo fastest, the faster the heat gets to the turbo, the less lag.

When I am cruising in my truck, if the pyro is reading up near 7-800, and I get after it, boy it sure does light instantly, but try lighting it down near 500, no way.....

 

More energy is expelled.through the exhaust than is actually harnessed into forward motion. . . .this means there is a PHENOMENAL amount of energy passi.g through the turbo. . . . .i.e. heat. Air alone is not spinning the.turbo 200,000+ rpm. . . . .it goes back to the candle/propeller comparison. The candles prob release 1 btu a piece and that spins the prop. There is 70-90,000 btu of thermal energy passing through the turbo. A mere 40 psi of drive pressure cannot provide that kinda energy. . . . . . . . .

 

Now, I don't know all the actual specs, and not going to look everything up, but I'm gonna throw some stuff out there quickly:

T444E = about 55.5CI per cylinder.

2000RPMs = roughly 111,000CI of air expelled per minute. (64 cubic feet per minute)

Engine Compression is 17:5:1.

Thats a lot of air, and a lot of pressure.

 

How does it get the air volume and the pressure?
Through Thermal energy.



I think the most confusing part is that the turbo acts like an external combustion engine, not like an internal one.

 

Exactly, pressure spins the turbo. As the air cools off it is losing volume, thus the closer to the engine the better.

 

engine compression has little to do with drive pressure. . .

the air and pressure is a result of combustion, not independant of it.

 

40 PSI definately CAN !

A lot more exhaust leaves the engine than air going in, because the combustion created heat and expanded gasses.

40 PSI is only 1 part of the equation, theres also velocity. Sort of like comparing HP and TQ, 40 PSI in a container can have minimal energy, while 40 PSI @ 1000's of cubic feet per minute could mean huge power being available.

The exhaust pressure acting on the vanes of the turbo is in fact the ONLY force causing it to spin.

The engine is creating pressurised heated air, and as it travels through the vanes, the force is exerted.

This is maybe why we seem to be disagreeing,
YES, the entire system depends on heat to operate,
NO , the actual turbocharger does not, it relies on pressure, which IS provided by heat.