Theoretical turbo question

Flight Service wrote: This was always clear to me: First Law of Thermodynamics The first law of thermodynamics states that, as a system undergoes a change of state, energy may cross the boundary as either heat or work, and each may be positive or negative. The net change in the energy of the system will be equal to the net energy that crosses the boundary of the system, which may change in the form of internal energy, kinetic energy, or potential energy. The first law of thermodynamics can be summarized in the equation: is the change in internal energy (This is enthalpy) is the change in kinetic energy (this is velocity of the air, with the exception of a smaller inlet than the outlet, this stays close to the same as the inlet speed, with the exception of a small amount of compression between the compressor wheel and the engine. This is why there is more lag in rear bumper mounted turbos and why turbos like no mufflers. This is very close to zero.) is the change in potential energy (it ain't getting ready to jump off a cliff so this is zero) is the work done by the system during the process (This is the side that compresses the intake side) All that being said, what does the work? Enthalpy. So that equation boils down to. = It's the heat, not the movement of the air, where the turbo makes most it's power. This is also why turbos get so hot. It really is cool when you think about it.

Turbos run by converting kinetic energy in the exhaust gas to kinetic energy in the turbo shaft. Heat is a means to an end of powering the air pump that pushes the exhaust gas through the turbo. Heat loss before a turbo only matters because density will go up and pressure will go down, and thus speed (kinetic energy) of AIR MOVEMENT across a given restriction for a given mass flow, will go down. It is important to retain total energy in the system, but you can spool a turbo with enough cold air. You CANT spool a turbo by just putting it in an oven. Heat is a means to an end. The end is putting kinetic energy into the exhaust gas.

This is why i think engineers are not any better than anyone else at explaining turbos. You can have movement of low-temperature air across a turbine and spin a turbo. You cannot have high temperature air without movement and still spin a turbo. Heat is just a means of generating the pressure differential across the turbine that creates the air movement that actually drives the turbo. Heat is important to the whole system, but the turbo itself does not run directly on heat anymore than my car runs directly on unrefined crude oil sitting underground in Saudi Arabia. There is pumping and changes of state that have to happen in between.

you are both sort of right. Heat loss and gain pays a big role in how a turbo works, but flow is the main driver.

Fueled by Caffeine wrote: you are both sort of right. Heat loss and gain pays a big role in how a turbo works, but flow is the main driver.

You got that backwards.

Seriously, got the degree in engineering to prove it. Spent and entire week in thermo just on turbo theory (strangely enough all of these arguments were put forward there, by the professor, knowing what would be said and what we have to defend. P.S. Damn you for making me remember that bastard.) Enthalpy, (Enthalpy is a defined thermodynamic potential, designated by the letter "H", that consists of the internal energy of the system (U) plus the product of pressure (p) and volume (V) of the system) is the primary source of power, kinetic energy (KE = (1/2)mass*velocity^2) is the second. Yes, the wind blowing does get it moving, but that is not what generates a MAJORITY of the power.

As with most conversions, it needs something to get it started, that is where the exhaust kinetic energy comes into play. Just to get it started.

Let me put it more intuitively.

If you have ever played with a properly sized turbo engine, you know you do not generate full boost until the engine is loaded. This is especially noticeable on diesel engines. Why? The engine is moving the same amount of air if you are standing on the throttle trying to challenge some one at Race Wars as you are running to top speed.

What changed? Load. The increased load requires, increased fuel, which creates increased heat, which spins the turbo faster. The volume of air available doesn't change because it is a fixed system dictated by displacement, valves, cams and volumetric efficiency of the design. Those are fixed items. Just the amount of fuel is changed.

If no one believes me, that is OK you choose to be wrong, some people choose to eat paint chips. But this isn't VTEC forums.
Here are some links.

TURBO THEORY (please notice all the references to HOT)

White paper on Analysis of a Turbocharger System for a Diesel Engine (if you really want to learn something)

He's probably played with a few turbos. Believe that's what he does for a living.

The engine doesn't move the same flow at full load vs just cruising at the same RPM, either.

Why? Because turbo.

In reply to Swank Force One:

Before September 8th it was

Flight Service wrote:

Fueled by Caffeine wrote: you are both sort of right. Heat loss and gain pays a big role in how a turbo works, but flow is the main driver.

You got that backwards. Seriously, got the degree in engineering to prove it.

ohh.. so the potential energy dosen't come from the gas flow? but only heat?

Sorry, you are so right. You know what's funny. That white paper you mentioned has an He351ve as the test subject in it, neat turbo. The paper dosen't touch anything with the turbine stage, where you know.. the PE is converted into KE...

but hey.. what the hell do I know. I was only part of the product launch team for the He351ve at Holset's Charleston turbo factory and an onsite design expert.. (also with a mechanical engineering degree).

I'll just stop talking cause obviously I'm wrong.

In reply to Fueled by Caffeine:

You have admitted it, that is the first step.

I'm more interested in what magical turbo motor produces the same airflow at a given RPM regardless of load. Never heard of such a thing.

this thread hurts my head.

Yes. heat matters. but a turbo is a simple Energy In energy out scenario.

Heat loss across the turbine is an indication of the amount of power being extracted from a gas flow.

Turbos are kept on the exhaust manifold to gather as much power from the expansion of that gas as it cools.

but it's a simple flow device.

Right, no argument there. Where the energy comes from, Enthalpy or Kinetic Energy is the argument.

I say Enthalpy, you are arguing for Kinetic Energy. I have heat, pressure, and internal disorder. Your argument has the mass of air and combustion by products and velocity.

Who has more?

I am a degreed mechanical engineer too, and I have something to add to this discussion.

My turbine wheels (and compressor wheels) are way bigger than yours, na na na!

And Swank, I don't think even an F2T can spool that turbine

tuna55 wrote: I am a degreed mechanical engineer too, and I have something to add to this discussion. My turbine wheels (and compressor wheels) are way bigger than yours, na na na! And Swank, I don't think even an F2T can spool that turbine

That was my last employer's motor. I did Overhaul and repair work on some cool stuff that powers..

yup.. I don't know what I'm talking about.

Flight Service wrote: Who has more?

The guy with 10 years industry experience or the guy who took a class once that potentially covered something in depth for one week?

Dunno. Tough choice.

Fueled by Caffeine wrote:

Flight Service wrote: Who has more?

The guy with 10 years industry experience or the guy who took a class once that potentially covered something in depth for one week? Dunno. Tough choice.

Sorry I don't have ten years, but I do have 6 and a class does that count? Your failure and/or deliberate refusal to answer the question of which contributes more, Enthalpy or KE, gives me all the answer I need.

Tuna55 wins, can I get one of those in time for Race Wars?

Flight Service wrote:

Fueled by Caffeine wrote:

Flight Service wrote: Who has more?

The guy with 10 years industry experience or the guy who took a class once that potentially covered something in depth for one week? Dunno. Tough choice.

Enthalpy or KE

Contradictory question. All energy is potential until going through the device. Kinetic energy is the only one in the shaft.. which is all anyone actually cares about.

Please take another class.

Flight Service wrote:

Fueled by Caffeine wrote:

Flight Service wrote: Who has more?

The guy with 10 years industry experience or the guy who took a class once that potentially covered something in depth for one week? Dunno. Tough choice.

Sorry I don't have ten years, but I do have 6 and a class does that count? Your failure and/or deliberate refusal to answer the question of which contributes more, Enthalpy or KE, gives me all the answer I need. Tuna55 wins, can I get one of those in time for Race Wars?

There's one being tested now, but you'd have to pay dearly to get it out of the hands of the engineers, plus it's already sold. It does make something like 530,000 horsepower, though.

Look.. I know what you are doing. You're smacking Euler's equation on the sucker and saying done.

All I'm saying is that it's a bit more complicated than that especially when transients are to be considered.

Equation 17 in here is the turbine work equation. In an ideal world.. set that equal to equation 11.. Wt=Wc kinda. get it.

http://users.ntua.gr/vgiakms/pdf/Energy_04.pdf

you cannot assume mdot stays constnt across the device because the density of the exhaust gas is changing as it cools rapidly.

Jesus.. you're making me remeber stuff that i did nearly 6 years ago..

Fueled by Caffeine wrote:

Flight Service wrote:

Fueled by Caffeine wrote:

Flight Service wrote: Who has more?

The guy with 10 years industry experience or the guy who took a class once that potentially covered something in depth for one week? Dunno. Tough choice.

Enthalpy or KE

Contradictory question. All energy is potential until going through the device. Kinetic energy is the only one in the shaft.. which is all anyone actually cares about. Please take another class.

Apparently given you just contradicted 6 years of experience with 2 global diesel engine companies and one actually built turbos, education from 4 top 30 university professors, and every single application calculation I have ever seen, 2 thermo books, and the 1st law of thermodynamics.

E36 M3. I need to see if gravity still works right.

Yo dawg, I heard you like turbines...

Wow, two of 'em!

Can we stop arguing now?

Fueled by Caffeine wrote: Look.. I know what you are doing. You're smacking Euler's equation on the sucker and saying done. All I'm saying is that it's a bit more complicated than that especially when transients are to be considered. Equation 17 in here is the turbine work equation. In an ideal world.. set that equal to equation 11.. Wt=Wc kinda. get it. http://users.ntua.gr/vgiakms/pdf/Energy_04.pdf you cannot assume mdot stays constnt across the device because the density of the exhaust gas is changing as it cools rapidly. Jesus.. you're making me remeber stuff that i did nearly 6 years ago..

No. I am putting things where they go. In the first Law of Thermo. I am not calculating losses in the system (which go to heat, BTW), why would I use Euler's?

Kinetic energy involves 2 things. Mass and velocity. nothing else, period, end of story, no etc., no buts, no ands, no or's, nothing else.

Enthalpy is Heat, Pressure, and all the other little things go bump in the gas.

Kinetic Energy is the movement of the air, everything else is Enthalpy. Seriously.

Flight Service wrote:

Fueled by Caffeine wrote: Look.. I know what you are doing. You're smacking Euler's equation on the sucker and saying done. All I'm saying is that it's a bit more complicated than that especially when transients are to be considered. Equation 17 in here is the turbine work equation. In an ideal world.. set that equal to equation 11.. Wt=Wc kinda. get it. http://users.ntua.gr/vgiakms/pdf/Energy_04.pdf you cannot assume mdot stays constnt across the device because the density of the exhaust gas is changing as it cools rapidly. Jesus.. you're making me remeber stuff that i did nearly 6 years ago..

No. I am putting things where they go. In the first Law of Thermo. I am not calculating losses in the system (which go to heat, BTW), why would I use Euler's? Kinetic energy involves 2 things. Mass and velocity. nothing else, period, end of story, no etc., no buts, no ands, no or's, nothing else. Enthalpy is Heat, Pressure, and all the other little things go bump in the gas. Kinetic Energy is the movement of the air, everything else is Enthalpy. Seriously.

You are getting confused. I state multiple times that turbos work on flow. Mass flow. And I'm getting confused with that stupid enthalpy entropy E36 M3. So we're both effectively right.

How's that for an ending.

I hate engineers.

@Flight Service. You are being very narrow minded here. From a layman's stand point, which is all I'm claiming to be, a turbo will do nothing if you heat it. Lets take a Turbocharger (Of any variety) and put it in a kiln at 1000 degrees and see what kind of boost pressure it produces. My hypothesis is it will just sit there. It has heat, why is it not working?

A turbo, for all people in the physical world, (and just as Fueled By Caffeine Stated) is a simple energy in and energy out system. Yes there are a million variables. Yes heat makes a difference.

I'm done, go run a CAD flow diagram and get more experience while I turbocharge another car successfully.

NordicSaab wrote: I hate engineers. @Flight Service. You are being very narrow minded here. From a layman's stand point, which is all I'm claiming to be, a turbo will do nothing if you heat it. Lets take a Turbocharger (Of any variety) and put it in a kiln at 1000 degrees and see what kind of boost pressure it produces. My hypothesis is it will just sit there. It has heat, why is it not working? A turbo, for all people in the physical world, (and just as Fueled By Caffeine Stated) is a simple energy in and energy out system. Yes there are a million variables. Yes heat makes a difference. I'm done, go run a CAD flow diagram and get more experience while I turbocharge another car successfully.

This is why engineers are mostly introverts. Broad based statements with no accuracy.

Try to successfully boost your car by putting the intercooler between the engine and the turbo, cooling the exhaust before it gets to the turbo.

See how well it works.

I am gonna steal FbC words here. "It's not that simple"

I will try to put it in laymens terms.

The air moving out of a cold engine, starts the turbo turning. Now we have motion of the turbine. The engine heats up and the turbo starts to spin faster. The heat and pressure expand in the turbo housing causing it to spin faster than the exhaust is coming out of the engine. This gives it the power to add pressure to the intake charge. Because the flow velocity (not mass flow rate) of the exhaust would be the same as the intake if it wasn't pressurized from the heat.

Flight Service wrote: Try to successfully boost your car by putting the intercooler between the engine and the turbo, cooling the exhaust before it gets to the turbo.

Remote mount turbos are effectively what you have described. They work. Now, in my youth I argued about how they were innefficent or not thermodynamically ideal.. But now.. I say. they work but are not ideal.

If I follow what you are saying a remote mount turbo wouldn't work because there is little "heat" available..

http://ststurbo.com/why_rear_mount.php