How does Turbo Turbine map work ?
04-08-2015, 08:26 PM
#28
Volume drives the turbine, the restriction (nozzle and wheel) create the differential pressure. Mass is what we use instead of volume on the map, because temperature assumptions are made.
This is exactly how jet engines work, except they just toss fuel in the air to make the volume change without the mess of pistons or rotors in the middle.
This is exactly how jet engines work, except they just toss fuel in the air to make the volume change without the mess of pistons or rotors in the middle.
04-08-2015, 08:38 PM
#29
Volume drives the turbine, the restriction (nozzle and wheel) create the differential pressure. Mass is what we use instead of volume on the map, because temperature assumptions are made.
This is exactly how jet engines work, except they just toss fuel in the air to make the volume change without the mess of pistons or rotors in the middle.
This is exactly how jet engines work, except they just toss fuel in the air to make the volume change without the mess of pistons or rotors in the middle.
04-08-2015, 09:00 PM
#30
Apples and oranges. Mass flow creates power in the engine because it needs it for oxygen for combustion. Differential temperature makes the power in the turbo because it needs it for the volume change. Run higher EGTs and you provide more volume at the same mass flow: turbine spools faster.
04-08-2015, 09:16 PM
#31
Apples and oranges. Mass flow creates power in the engine because it needs it for oxygen for combustion. Differential temperature makes the power in the turbo because it needs it for the volume change. Run higher EGTs and you provide more volume at the same mass flow: turbine spools faster.
04-08-2015, 09:34 PM
#32
OK a simple example. Take a jet engine. Just a compressor tied to a turbine with a shaft and a combustion chamber in between. You can blow as much air as you want through it and mass in will equal mass out. If you spin it up until it is using 50lbm/min air flow it will just spin back down again once you take the air away. If you spin it up with 50lbm/min air and heat the air in the combustion chamber it can become self sustaining and even gain power and flow. Without temperature multiplying volume a turbocharger won't work. Just like without heat raising combustion gas pressure a piston engine won't work.
04-08-2015, 10:44 PM
#33
I prefer to think of it simply . You need power to drive a turbine . That power comes from air hitting the turbine . If the air has no mass ....turbine wont spin and no power is made .
If temperature is increased you need more volume flow to create the same mass flow but mass flow stays the same at the same turbine speed .
If temperature is increased you need more volume flow to create the same mass flow but mass flow stays the same at the same turbine speed .
04-09-2015, 03:24 AM
#35
OK a simple example. Take a jet engine. Just a compressor tied to a turbine with a shaft and a combustion chamber in between. You can blow as much air as you want through it and mass in will equal mass out. If you spin it up until it is using 50lbm/min air flow it will just spin back down again once you take the air away. If you spin it up with 50lbm/min air and heat the air in the combustion chamber it can become self sustaining and even gain power and flow. Without temperature multiplying volume a turbocharger won't work. Just like without heat raising combustion gas pressure a piston engine won't work.
You both need to quit arguing/posting and instead get your head wrapped around the actual subject matter clearly. Just a friendly suggestion.
.
04-09-2015, 09:44 AM
#38
http://en.wikipedia.org/wiki/Brayton_cycleA turbocharger just like a jet engine runs of a Brayton cycle.
There have even been closed Brayton cycle nuclear plants using hydrogen or helium as the medium.
04-09-2015, 07:34 PM
#39
Why do we keep bringing temperature into it.... it's the pressure differential that does the work.
Bernoulli principle anyone? Temperature of exhaust matters because it INCREASES the pressure differential. If the post turbo exhaust pressure were somehow increased to several hundred PSI, the temperature of the pre-turbo exhaust would not matter. The system would break down.
In any energy transfer.....ANY, heat is a byproduct of inefficiency. Conservation of mass simply illustrates that the MASS of intake and turbine are the same (small change to accommodate fuel), and therefore the mass required to spin a turbine is directly related to the mass it can efficiently compress. The mass in the turbine map is more useful because the pressure differential is already assumed in the engineering of the shape of the blades. Therefore, in a perfect world, mass in, mass out. Rotaries break the mold because the pressure differential is not the same as an equal piston due to the lack of a dead cycle in the motor.
Bernoulli principle anyone? Temperature of exhaust matters because it INCREASES the pressure differential. If the post turbo exhaust pressure were somehow increased to several hundred PSI, the temperature of the pre-turbo exhaust would not matter. The system would break down.
In any energy transfer.....ANY, heat is a byproduct of inefficiency. Conservation of mass simply illustrates that the MASS of intake and turbine are the same (small change to accommodate fuel), and therefore the mass required to spin a turbine is directly related to the mass it can efficiently compress. The mass in the turbine map is more useful because the pressure differential is already assumed in the engineering of the shape of the blades. Therefore, in a perfect world, mass in, mass out. Rotaries break the mold because the pressure differential is not the same as an equal piston due to the lack of a dead cycle in the motor.
04-09-2015, 08:09 PM
#41
Why do we keep bringing temperature into it.... it's the pressure differential that does the work.
If the post turbo exhaust pressure were somehow increased to several hundred PSI, the temperature of the pre-turbo exhaust would not matter. The system would break down.
In any energy transfer.....ANY, heat is a byproduct of inefficiency.
If the post turbo exhaust pressure were somehow increased to several hundred PSI, the temperature of the pre-turbo exhaust would not matter. The system would break down.
In any energy transfer.....ANY, heat is a byproduct of inefficiency.
Heat is the byproduct of inefficiency of higher forms of energy, but it's also the starting point. Turning heat into something useable is the basis for all heat engine, including the otto cycle which turns our engine, and the brayton cycle which turns our turbo.
If you guys don't get this then it will shock you to know that in many cases the pressure in the charge pipe is higher than the exhaust pressure going into the turbo . What pressure is driving the turbo then?
Edit:
Since you guys don't like my answers and can't be bothered to look at the links I posted, answer me this question: What powers the turbo?
If it's a change in mass from fuel, then will the turbo work if you aren't igniting the fuel (either with a spark plug or pressure)?
If it's pressure from the engine, then why doesn't the engine lose HP similar to a supercharger?
If it's something else then where does the energy come from?
Simple right?
Last edited by Harlan; 04-09-2015 at 08:16 PM.
04-09-2015, 08:52 PM
#42
*The pressure differential from one side of the turbine to the other is what forces the air through the turbine .
*The inertia of the air hitting the turbine blades is where the energy to power the wheel comes from .
*That inertia is dependent on the mass and velocity of the air molecules .
*Hotter air has less mass density so needs a higher velocity to create the same inertia .
*which in turn means volume flow is higher .
*mass flow stays the same because inertia is directly proportional to mass and velocity .
*The inertia of the air hitting the turbine blades is where the energy to power the wheel comes from .
*That inertia is dependent on the mass and velocity of the air molecules .
*Hotter air has less mass density so needs a higher velocity to create the same inertia .
*which in turn means volume flow is higher .
*mass flow stays the same because inertia is directly proportional to mass and velocity .
Last edited by Brettus; 04-09-2015 at 09:51 PM.
04-09-2015, 09:22 PM
#45
And I need to know that because it's vital to the design of the manifold i'm considering . Anywhere from 40-50% at peak flow should work well but higher than 50 ...not so good.
So yes ...... For me it's practical information I'll apply and not just a futile argument for the sake of it .
Last edited by Brettus; 04-09-2015 at 09:57 PM.
04-09-2015, 09:59 PM
#46
Watch the first 5minutes of this video or not. This is pretty basic stuff to understanding where the energy to drive the turbo comes from, and why temperature matters.
I'm done debating it. I really want you guys to understand because this is important to designing and sizing systems, but it's pointless to derail this thread further over conceptual errors. Good luck understanding how it all works together without understanding why.
I'm done debating it. I really want you guys to understand because this is important to designing and sizing systems, but it's pointless to derail this thread further over conceptual errors. Good luck understanding how it all works together without understanding why.
04-10-2015, 12:22 AM
#48
Ok Harlan , I just wasted 5 mins of my life watching that video .I was very disappointed because It has very little to do with what we are talking about . It is describing a complete system and very little about what happens at the turbine to convert airflow to power (there was one sentence that was relevant). You may as well have posted a video of you clipping your toenails for all light that one shed on the subject.
I looked at your video so how about you do this thing for me :
Go through my post #42 above and see if you can argue against any one single point I made in that explanation .
I looked at your video so how about you do this thing for me :
Go through my post #42 above and see if you can argue against any one single point I made in that explanation .
Last edited by Brettus; 04-10-2015 at 02:32 AM.
04-10-2015, 08:20 AM
#49
The video has everything to do with what we are talking about, but you aren't seeing it yet. The exhaust housing is part of a complete system. The engine is just the heat source as far as the turbo is concerned.
Here is my response to post #42
Without the restriction (exhaust housing) raising the velocity of the air there is nothing to cause a pressure difference. So in reality it is the flow that is restricted which causes the differential pressure, but this is done to raise the kinetic energy of the exhaust gas. It’s kinetic energy of the exhaust gas that spins the turbine. Inertia (or rather momentum) is not a measure of energy.
E=1/2mv^2
Sure mass is important, but the velocity is exponentially important. If you ran 50lbm/min of water through a turbine it would spin slowly, if you ran 50lbm/min of steam through the same turbine it would spin much faster. Because the water (1000 times the density) moves very slowly through the same pipe at the same mass flow.
Hotter air traveling through the same size pipe at the same mass flow must move at a higher velocity. Higher velocity means more kinetic energy. Again it’s exponential so if you cut the density in half you double the velocity and the energy in the system goes up by 4.
The differential pressure through a restriction is exponential with volumetric flow. This causes there to be point of futility when trying to push more volume through the same hole. We see that on the turbine map as pressure goes up but flow stays nearly constant.
This is a bit of an oversimplification using classical mechanics, but the fundamentals hold true.
Here is my response to post #42
Without the restriction (exhaust housing) raising the velocity of the air there is nothing to cause a pressure difference. So in reality it is the flow that is restricted which causes the differential pressure, but this is done to raise the kinetic energy of the exhaust gas. It’s kinetic energy of the exhaust gas that spins the turbine. Inertia (or rather momentum) is not a measure of energy.
E=1/2mv^2
Sure mass is important, but the velocity is exponentially important. If you ran 50lbm/min of water through a turbine it would spin slowly, if you ran 50lbm/min of steam through the same turbine it would spin much faster. Because the water (1000 times the density) moves very slowly through the same pipe at the same mass flow.
Hotter air traveling through the same size pipe at the same mass flow must move at a higher velocity. Higher velocity means more kinetic energy. Again it’s exponential so if you cut the density in half you double the velocity and the energy in the system goes up by 4.
The differential pressure through a restriction is exponential with volumetric flow. This causes there to be point of futility when trying to push more volume through the same hole. We see that on the turbine map as pressure goes up but flow stays nearly constant.
This is a bit of an oversimplification using classical mechanics, but the fundamentals hold true.
04-10-2015, 10:13 AM
#50
Driving my unreliable rx8
force= mass x acceleration
If you heat it up then the mass per volume becomes less and the acceleration increases proportional to each other so the force would remain constant.
If you heat it up then the mass per volume becomes less and the acceleration increases proportional to each other so the force would remain constant.