Sounds like you took from school what you needed. Turn a wrench and you'll be two steps ahead of most 2-dimensional engineering graduates.
BillyM;1048808 said:
Turbo Size psi/volume
- Thread starter FlikRacing
- Start date
BillyM is completely right I say amen brother.
Also I would like to point out that boost is merely a restriction to flow and is really pointless and unused in any performance calculations that matter. You can not use boost to figure anything out because it is an answer to an equation not a variable to be plugged in in order to solve one.
Also I would like to point out that boost is merely a restriction to flow and is really pointless and unused in any performance calculations that matter. You can not use boost to figure anything out because it is an answer to an equation not a variable to be plugged in in order to solve one.
I don't think anyone who has claimed volume is proportional to boost has ever looked at a compressor map. If they had they would notice that for a specific mass flow there are a huge spread of available pressure ratio's.
Its all about MASS of air, MASS of fuel forget about volume.
Its all about MASS of air, MASS of fuel forget about volume.
Big Rob;1060326 said:
huh?
MASS of air is only PART of the overall equation.
DENSITY which is related to Temprature is also needed.
Err... you feeling ok today, dude? You've got it backwards, which is odd for you. Temp is used to calculate density, and density is used to calculate mass. Unless my memory deceives me...figgie;1075194 said:
Mass is the final number, presure x density = how many molecules...
Figgie wrong, Grim right...
--billyM
Figgie wrong, Grim right...
--billyM
BillyM;1076966 said:
Say what?
What physics/chemistry class where you paying attention to?
Mass does not change. Mass is constant for a given element/chemical (come on this is basics physics!). 1mole of N2 (28.012 Mass Units) + O2 (31.998 Mass Units) is the same wether it is measured here, on planet earth, the moon, jupiter or deep space. Come on! this is one of the first things physics teaches. Mass does not change! Weight does!
As for Pressure?
You ALMOST got it right.
The equation is Mass, Volume Density = Mass(kg or moles) x VOLUME which is no where near the same as pressure. We are not dealing with static gas here!
mass is only calculated for an unknown gas or unless you feel like finding out why the answer is the way it is
Grim
the atmosphere we breath is well known Mass wise (N2 + O2 + traces of the rest). 1.229kg/m^3. There is zero need to calculate mass volume density unless you want to take it down at the mole level.
Agreed on the mass not changing bit. However, the volume and pressure do change, by quite a bit, depending on location.
Air at sea level isn't even vaguely close to what is in my intake manifold at 20 pounds of boost.
I currently run MAP, which uses a temperature sensor and a pressure sensor to calculate the mass of the air entering the engine and the ECU adjusts fuel injection to match. I'd have to go look up the ideal gas law as I haven't been in school for 20+ years, but I'd suspect that it'll tell me I can derive mass from pressure and temperature.
Air at sea level isn't even vaguely close to what is in my intake manifold at 20 pounds of boost.
I currently run MAP, which uses a temperature sensor and a pressure sensor to calculate the mass of the air entering the engine and the ECU adjusts fuel injection to match. I'd have to go look up the ideal gas law as I haven't been in school for 20+ years, but I'd suspect that it'll tell me I can derive mass from pressure and temperature.
GrimJack;1097210 said:
Grim,
PV=mRT --> (m/v) = [P/(R*T)] = density
R is constant. You car knows the pressure and temperature, which gives the density. Engine speed determines the rate at which air leaves the manifold, giving a volume. Multiply by that ECU-calculated volume, and there you have mass.
Grim
Actually, the only thing that really has changed at sea level v. the 1+ atmosphere inside of your manifold is absolute pressure.
Barometric compensation - compensates for the density due to altitude if you use it that is. If you do use it, it helps in adjusting for changing exhaust velocity due to the lack of atmosphere hindering the exhaust on it's way out.
Hence why turbo props can go to 20k+ feet and still remain running.
300kpa inside of your manifold stays the same if it is 300kpa @ sea level or 300kpa @ 30k feet.
Actually, the only thing that really has changed at sea level v. the 1+ atmosphere inside of your manifold is absolute pressure.
Barometric compensation - compensates for the density due to altitude if you use it that is. If you do use it, it helps in adjusting for changing exhaust velocity due to the lack of atmosphere hindering the exhaust on it's way out.
Hence why turbo props can go to 20k+ feet and still remain running.
300kpa inside of your manifold stays the same if it is 300kpa @ sea level or 300kpa @ 30k feet.
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It won't be the same, higher up, you will be running a greater pressure ratio to achieve the same manifold pressure. By going from sea level to somewhere way above sea level, you will likely be running at a reduced efficiency, as you start pushing higher up on the compressor map.figgie;1097354 said:300kpa inside of your manifold stays the same if it is 300kpa @ sea level or 300kpa @ 30k feet.
I always calculate using 13.5psi (instead of 14.7) base atmospheric pressure to compensate for my altitude when doing flow calculations..
annoyingrob;1097810 said:It won't be the same, higher up, you will be running a greater pressure ratio to achieve the same manifold pressure. By going from sea level to somewhere way above sea level, you will likely be running at a reduced efficiency, as you start pushing higher up on the compressor map.
I always calculate using 13.5psi (instead of 14.7) base atmospheric pressure to compensate for my altitude when doing flow calculations..
Incorrect!
It WILL be the same.
The pressure ratio is irrelevant to achieving said 300kpa. Now your example shows only that it will take more WORK to achieve said 300kpa but in the end. If it take .5 times the work or 1000x the work. As long as it is 300kpa inside of the manifold. 300kpa will be measured anywhere inside of the manifold, if is a Death valley or if it is 75 miles above this planet's surface.
so since you did bring it up.
Show through equation why 300kpa inside of the intake manifold be the same regardless of altitude (I am even going to make it easy for you. sea level and 30k feet is fine).
and just so we are on the same page.
kpa = kilopascals ABSOLUTE
figgie;1098017 said:Incorrect!
It WILL be the same.
The pressure ratio is irrelevant to achieving said 300kpa. Now your example shows only that it will take more WORK to achieve said 300kpa but in the end. If it take .5 times the work or 1000x the work. As long as it is 300kpa inside of the manifold. 300kpa will be measured anywhere inside of the manifold, if is a Death valley or if it is 75 miles above this planet's surface.
so since you did bring it up.
Show through equation why 300kpa inside of the intake manifold be the same regardless of altitude (I am even going to make it easy for you. sea level and 30k feet is fine).
and just so we are on the same page.
kpa = kilopascals ABSOLUTE
Figgie, PLEASE give up on this thread. The point was made many posts back by BillyM.
annoyingrob is right about the pressure ratio, as were most of the other posts that you argued over their theory.
This thread had great info and it's getting tailed with banter. People like to search and find answers without having to read a ton of info that doesn't matter. Mods should delete everything after BillyM's post.
/thread.
87witmoreboost;1098024 said:
I don't think so.
I deal with facts and in this case Physics along with Thermodynamics.
last I checked.
Ideal gas laws, though used incorrectly in this post as we are not dealing with a perfectly static gas is a law not a "theory".
Same with Avograda and Boyle's law which all can be used here though incorrectly.
So seeing as that information that you and annoyingrob posted is infact incorrect. My job is to correct you.
So as I posted to annoyingrob and now you.
Show us through equation why 300kpa inside the manifold @ what altitude X is not the same ( != ) as 300 kpa inside the intake manifold @ altitude Y. How it gets there is at this point irrelevant. Once you figure that out. Then you can put in can turbo X get there efficently, same with Turbo y and turbo z.
and if that is to much work.
How much work does turbo x need to do to flow y cfm @ alt a, @ alt b. (that is assuming that it can flow efficent enough to even get there).
Actually we don't even have to use turbos.
How does an airplane calculate air speed at altitude (the old fashion way of pitot static tubes). How about altitude? Angle of attack?
Btw this is really just a setup question for you two to understand what is actually happening inside of the "system" (which happens to be an engine in this case).
Pressure * density is not only wrong it is INCOMPLETE. You can ask for a delete but it is not happening when the information provided by you two is just flat out incomplete hence why I am asking for an equation solution with real numbers and not typing
also keep in mind.
this is the Turbocharge SME sub-forum not the Turbocharger speculation or best guess sub-forum.
GrimJack;998489 said:
I can!
You should come over the EFI101 forums where it is constant.
BillyM got it right on post #7.
BillyM said:
Then he does not heed his own words in post #26
BillyM;1076966 said:
Contradictory since temprature is nowhere to be found..... odd though as he did mention it prior.
Oh well.
You should see when the topic, Barometric Compensation: Needed on a standalone or not comes about. I have "discussed" this subject with Jason S (AEM now doing the Pro_EFI) and he never backdown from the BACP not being needed. Talk about fun discussion!
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figgie;1098037 said:I don't think so.
I deal with facts and in this case Physics along with Thermodynamics.
last I checked.
Ideal gas laws, though used incorrectly in this post as we are not dealing with a perfectly static gas is a law not a "theory".
Same with Avograda and Boyle's law which all can be used here though incorrectly.
So seeing as that information that you and annoyingrob posted is infact incorrect. My job is to correct you.
So as I posted to annoyingrob and now you.
Show us through equation why 300kpa inside the manifold @ what altitude X is not the same ( != ) as 300 kpa inside the intake manifold @ altitude Y. How it gets there is at this point irrelevant. Once you figure that out. Then you can put in can turbo X get there efficently, same with Turbo y and turbo z.
and if that is to much work.
How much work does turbo x need to do to flow y cfm @ alt a, @ alt b. (that is assuming that it can flow efficent enough to even get there).
Actually we don't even have to use turbos.
How does an airplane calculate air speed at altitude (the old fashion way of pitot static tubes). How about altitude? Angle of attack?
Btw this is really just a setup question for you two to understand what is actually happening inside of the "system" (which happens to be an engine in this case).
Pressure * density is not only wrong it is INCOMPLETE. You can ask for a delete but it is not happening when the information provided by you two is just flat out incomplete hence why I am asking for an equation solution with real numbers and not typing
also keep in mind.
this is the Turbocharge SME sub-forum not the Turbocharger speculation or best guess sub-forum.
I can!
You should come over the EFI101 forums where it is constant.
BillyM got it right on post #7.
Then he does not heed his own words in post #26
Contradictory since temprature is nowhere to be found..... odd though as he did mention it prior.
Oh well.
You should see when the topic, Barometric Compensation: Needed on a standalone or not comes about. I have "discussed" this subject with Jason S (AEM now doing the Pro_EFI) and he never backdown from the BACP not being needed. Talk about fun discussion!
You ARE correct about pressure not changing at different altitudes, assuming constant temp.
It is tiring to read your posts because you bounce all over the place with your theory. Point being, your rants arguing everyone about their technical engineering theory is unnecessary and at times, incorrect.
This was sweet thread up to the end of page 2. I hate to knock on you as you seem to have a good technical understanding of things, but it's just old now. Let this thread die so that when people search for information about pressure in larger turbo's, they can read all that they need in two pages. I am equally adding to the rant here, but it's an attempt to preserve this information.
Nothing personal, let it end.
87wit: No it's not going to be deleted.
Accept it that Figgie has taken the time to provide a complete answer and move on.
I'm quite happy to be corrected if I'm wrong about something and look at it as furthering my knowledge and will thank someone for educating me.
Accept it that Figgie has taken the time to provide a complete answer and move on.
I'm quite happy to be corrected if I'm wrong about something and look at it as furthering my knowledge and will thank someone for educating me.
figgie;1098037 said:
Typo on my part, I meant to say Volume x Density ...doesn't make you right though.
Mass is the final result. Volume x Density.
Density is a factor of Pressure & Temperature. <--there is where temperature went, it wasn't missing
...and the next person who says pressure-ratio doesn't matter, all that matters is total MAP, I add to my ignore list. Try sizing a turbo for a motor at sea level and then size one at 10,000ft. Pressure ratio is absolutely important. ...that is how you derrive the efficiency of the turbo, and thusly temperature. <--important
Figgie, you realize this whole arguement was started by symantecs, right? Big Rob wasn't saying "mass" as in the specific mass of air, he was saying total mass of the air in the cylinder, and he's 100% right in that. Mass is the final number. Yes, "the mass of air" is not the final answer, but the "mass of the air in the cylinder" is.
--billyM
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figgie;1098037 said:
Argue with you? OK!
With all else being equal, 300kpa is 300kpa is 300kpa. You are entirely corect with this, nobody is arguing that. What I AM arguing about is that not everything else is equal. Air temperature will be different within the manifolds.
Lets say at location A, air pressure is 100kpa. You want 200kpa in your manifold. That's a 2:1 pressure ratio your turbo needs to run at. At location B, air pressure is 60kpa. To achieve 200kpa in the manifold, the turbocharger is now running at a 3.3:1 pressure ratio.
Here's a compressor map of a Garrett GT40-88.
To create that 200kpa at location A, the turbocharger is running at 74% efficiency. To create 200kpa at lcoation B, the turbocharger is only running at 72% efficiency. The reduced efficiency of the compressor means that it's pumping more heat into your air charge. That means the air in your intake manifold, while still being the same 200kpa, is hotter.
And with your seemingly massive knowledge of thermodynamics, you understand that while at the same pressure, the hotter gas will have less density.
So there, my point is proven. It's not the same, it's less efficient. 300kpa at sea level will be a denser charge than 300kpa up in the sky, running the same motor and turbo, which you told me was wrong.
Guys, I seriously have a tear in my eye right now, reading all this (I'm so proud of the discussion!) I've got to go pick up a laptop, then I'll be back to straighten this out.
You guys all seem to be forgetting a very basic thing - these are equations, and they can be worked both ways.
In a given turbo system, volume WILL be static. If you increase mass of air, you MUST increase the density. Works the other way around - increase the density, you increase the mass.
Doesn't matter if it's by pressurization or temperature. The fact is, if you can make a CT26 and a PTE67 make 20psi of boost, you are not getting the same amount of power due to difference in temperature. If you have a PTE67 making 15psi and 20psi, you get differing power levels not so much according to temperature, but more due to the pressurization delta.
300kPa is 300kPa. I don't care if you make it here, or on the Moon. What IS different, however, is how much work it took to make that 300kPa (figgie hit this one) - if you are attempting to make 300kPa from a 100kPa atmospheric pressure, that takes a certain amount of work.
Making 300kPa from a 50kPa atmospheric pressure, takes much more work. This is reflected, as Ian pointed out, in the Adiabatic Tables. You can also calculate Adiabatic Efficiency with the flow map - map out your Pressure Ratio (which will take into consideration the atmospheric pressure you start with) and figure out your mass flow of air. X/Y coordinates that point right at your AE, provided other variables are held constant (you can look up and see what temperature points are used, but invariably, we can figure everything out if we know the atmospheric temperature and pressure at any given moment)
You guys all seem to be forgetting a very basic thing - these are equations, and they can be worked both ways.
In a given turbo system, volume WILL be static. If you increase mass of air, you MUST increase the density. Works the other way around - increase the density, you increase the mass.
Doesn't matter if it's by pressurization or temperature. The fact is, if you can make a CT26 and a PTE67 make 20psi of boost, you are not getting the same amount of power due to difference in temperature. If you have a PTE67 making 15psi and 20psi, you get differing power levels not so much according to temperature, but more due to the pressurization delta.
300kPa is 300kPa. I don't care if you make it here, or on the Moon. What IS different, however, is how much work it took to make that 300kPa (figgie hit this one) - if you are attempting to make 300kPa from a 100kPa atmospheric pressure, that takes a certain amount of work.
Making 300kPa from a 50kPa atmospheric pressure, takes much more work. This is reflected, as Ian pointed out, in the Adiabatic Tables. You can also calculate Adiabatic Efficiency with the flow map - map out your Pressure Ratio (which will take into consideration the atmospheric pressure you start with) and figure out your mass flow of air. X/Y coordinates that point right at your AE, provided other variables are held constant (you can look up and see what temperature points are used, but invariably, we can figure everything out if we know the atmospheric temperature and pressure at any given moment)