Help needed please: *Turbo gurus*-Turbocharger feasibility/restrictor impact analysis

[c5ho]

Hey everyone,
I was hoping someone would be able to point me in the right direction to get me started.

I am writing a report as to the feasibility of using a turbocharger in a future care for my school.

However, the faculty advisor is extremely concerned with the impact of the intake restrictor.

I know that other schools use a turbocharger so I would obviously think that there are still benefits and that the intake restrictor does not render a turbo useless.

How would I go about to begin to analyze the impact of the restrictor? I would like to examine the pressure drop across the restrictor and the effect on the mass flow of air due to it. Does that sound right? I would like to find out the necessary values in order to size the turbo according to the GT12 or GT15v data to prove that it would be in their operating ranges. What else should I examine?

My fluids is pretty rusty so I'm not sure what to do or where to begin. Can someone please shed some light?

Thanks in advance,

Calvin.

[c5ho]

Hey everyone,
I was hoping someone would be able to point me in the right direction to get me started.

I am writing a report as to the feasibility of using a turbocharger in a future care for my school.

However, the faculty advisor is extremely concerned with the impact of the intake restrictor.

I know that other schools use a turbocharger so I would obviously think that there are still benefits and that the intake restrictor does not render a turbo useless.

How would I go about to begin to analyze the impact of the restrictor? I would like to examine the pressure drop across the restrictor and the effect on the mass flow of air due to it. Does that sound right? I would like to find out the necessary values in order to size the turbo according to the GT12 or GT15v data to prove that it would be in their operating ranges. What else should I examine?

My fluids is pretty rusty so I'm not sure what to do or where to begin. Can someone please shed some light?

Thanks in advance,

Calvin.

[billywight]

Assume isentropic flow, then calculate the max volumetric flow rate for choked flow through the restrictor.

Then assume a reasonable volumetric efficiency for the engine at differnt RPM levels and figure out the volume flow it wants.

Compare the two values from above at various RPM levels and go from there. Just a hint though, most teams aren't doing forced induction just to look cool...

[Jonathan R.]

The turbo allows the air flow coming into the intake to reach supersonic speed into the intake. This way you build pressure in the plenum and have higher performance of the engine. But the if the flow passing the restrictor goes supersonic, you get a substantial total pressure loss at the restrictor.

[mangel83]

What would be a reasonable volumetric efficiency for a 4 cyl. 600cc restricted motorcycle engine.. I'm guessing between 55%-65% depending on intake design?

And what volumetric efficiency should one assume? The ve of a stock engine is different from the ve of a turboed restricted engine and from a NA restricted engine

[Kirk Feldkamp]

Think of %VE with respect to manifold conditions. This would put a 'normal' 600 at anywhere between 97% and 103% at peak VE. Your analysis should take the air from ambient, through the restrictor, through the turbo, and then through the intercooler (if applicable) and ducting. This will give you a resultant density in the plenum. If you know the %VE, you can determine the volume flow rate through the system. Combine that volume flow rate with the density, and you have mass flow rate. An air/fuel ratio and a BSFC later and you have a good approximation of power.

The tricky part is dealing with the turbine side... although the same sort of analysis can be done. Break the whole problem into chunks just like you do for any thermo-type problem.

Don't forget to work in corrected flow when dealing with the compressor and turbine maps!

-Kirk

[Wes Johnson]

In addition to your flow analyses don't forget to take into account the issues that arise from having the throttle plate before the compressor inlet.

Wes

Clemson FSAE

[Kirk Feldkamp]

There's an issue with that? Never heard of that! http://fsae.com/groupee_common/emoticons/icon_confused.gif

http://fsae.com/groupee_common/emoticons/icon_wink.gif

-Kirk

[mangel83]

I have the aproximate air mass flow rate range through the compressor (based on %ve, density and engine's rpm), now with this values I go to the compressor map and with the corrected air mass flow and the pressure ratio I want for my system I get the operating range for the compressor under those conditions (air mass flow rate, inlet pressure & temperature and desired PR), now I also have compressor efficiency and corrected rpm for the compressor, form this I can figure compressor outlet temp. and physical (real) rpm of my system.

Now the tricky part, the turbine part, from the previous calcs. and with air/fuel ratio I can figure turbine inlet temperature and actual gas flow through the turbine. With the temperature I find the corrected rpm for the turbine, and that's as far as I get.

I've tried finding the corrected gas flow for what I need turbine inlet pressure (wich I think depends on the turbine itself and the backpressure it generates on the system), anyway, based on engine thermodynamic cycle I've tried to calculate this (approximate)pressure in 3 different ways: 1. Cengel's Thermodynamics, 2. Ferguson's Internal Combustion Engines Applied Thermosciences & 3. Ideal Gas Equation (P.v=R.T; v & R for gasses from a spanish book based on afr) and in all 3 ways the values differ and come higher than expected based on boost pressure. On the other axis, expansion ratio, I think I could aproximate discharge pressure of the turbine maybe through some simulations of the exahust pipe or something although I haven't tried that, but even if I find this pressure I would still need turbine inlet pressure.

With the corrected rpm for the turbine I think there's nothing I can do with it given I don't have neither pressure ratio in the turbine, nor corrected gas mass flow.

I have read Corky Bell's Maximum Boost back and forth, but he doesn't say much about turbines, just some graphs about exducer bore and A/R ratio to size accordingly but that's no help at all. I've gone through some basic turbomachinery books as well but with no luck. I'm stuck at this point... Am I missing something or doing it the wrong way? I've searched the forums with little to no luck, could anyone shed some light here, maybe other ways to approach the problem, other resources to search, anything...

One other thing, I've been working with Garret's GT12 and GT15V maps, and on the GT15V turbine map there's a percentage value next to the rpm's, wich goes from 0.9 to 1.2 depending on rpm, what this % means?

[Kirk Feldkamp]

A few "hints"...

1. Use a "normal" EGT (there has been a lot of discussion about EGT on these forums) for your turbine inlet temp. I don't know what you came up with from your analysis, but just make sure it's a reasonable number.

2. Don't forget to add the mass of the fuel to your turbine mass flow. I think you did, but I just wanted to make sure.

3. Don't forget the wastegate! The turbine will always operate on the line given on the turbine map. Always remember that the turbine is simply supplying the power to the compressor via the shaft. You need to figure out how much power is required to make X pressure ratio and Y mass flow (your compressor operating point). Then you need to figure out how much 'expansion ratio' is required on the turbine side to produce that power. Make sure you take aero AND mechanical efficiency into account! You should be able to place this turbine operating point somewhere on the turbine map line at this point. However, if you now look at the corrected turbine mass flow you'll see that it's either above or below the line at any given engine and turbo operating point. If it's above the line, then the wastegate is 'venting' the difference in mass flow. If the point is below the turbine map line, you can't make the compressor PR with the input parameters you used. This is how you figure out where your "boost threshold" is. Also, corrected shaft speed is the only way to do RPM between the two maps...

4. Corky Bell's "Turbochargers" isn't an engineering book by any means. He didn't even go into compressor matching in that book! If you read his newer book "Supercharged!" he goes through and does it there correctly. From item #3 you can see why he probably didn't even attempt to go through a turbine match. I've heard from various people that Haywood goes through a match in his book "Internal Combustion Engine Fundamentals", but I've never seen it with my own two eyes, so I can't confirm that.

Generally I recommend people get all of the available turbine housings for a particualr turbo we sell because it is easier and more cost effective than floundering around on the dyno/track with the wrong turbine housing. Unfortunately, there are no alternatives available for the GT12 and GT15V, so you're stuck with what you've got. I would highly recommend finishing the matching exercise because you really do learn a lot more than just slapping on a turbo. Keep up the good work.

5. I don't know what those numbers are on the GT15V map... but I can ask around.

-Kirk

[mangel83]

Kirk, thanks for all the hints!
As for those hints:

1. I've been using EGT between 750ºC and 830ºC based mostly on what I've found in these forums, we have some thermocouples laying around in the shop, but we don't have any kind of dyno to work with yet, we're working on that. I've found some equations that predict egt based on afr and fuel low heat value and most of the time you can get good approximate results, although I'm not very fond of this equations, I just use them as a reference.

2. I did add the fuel mass to calculate turbine mass flow.

3. I have my compressor operating point (considering both aero and mech efficiencies), the problem arises in the "figuring the expansion ratio" part. According my calcs in order to find turbine pressure ratio I need to know the efficiency of the turbine, for GT12 I guess it would be ok to assume an efficiency around 60% since it stays pretty near that value throughout it's operating range. From here and assuming discharge pressure for the turbine (I'm thinking 5% to 10% above atmospheric, correct me if wrong) I find the turbine inlet pressure, then the corrected gas flow and voilÃ* I have the turbine operating point (Am I right?). But for the GT15V the efficiency range is quite different even though I think I could approximate an efficieny around the middle (55% maybe) and do the exactly same thing than before, but in this case I don't have a single line to compare it to, but a bunch of lines, I guess that as long as the turbine operating point falls somewhere inside the map, the turbo will work fine(I assume that if it falls below the map there won't be enough power available for the compressor, but what happens if it falls above it? ther's no wastegate to vent the system). I also have both, physical an corrected (compressor and turbine) rpm's, but not sure what to do with them anyway.

4. Those books you mention are quite difficult to find in this side of the world (at least here in my country) and since the team doesn't plan to go turbo in a near future I don't think I can get a hold of those books in a while. All this matching is just as a side project to establish some ground points if the team decides to go turbo in the future. Actually we believe that a competitive package, a "winning" package can be achieved without forced induction, many teams have proved that point, and I'm sure many more will.

5. It's not like it's a matter of life or death, but hey, if those numbers are there, there should be a reason

Edit: Some spelling mistakes

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by turbotwig:
There's an issue with that? Never heard of that! http://fsae.com/groupee_common/emoticons/icon_confused.gif

http://fsae.com/groupee_common/emoticons/icon_wink.gif

-Kirk </div></BLOCKQUOTE>
greatest post ever!!
I need to get a turbocharged engine calculator spreadsheet on here once I salvage my hard drive...computer crapped out on me...just need to host it...

[Dan G]

I think I got this from someone on here...

http://www.evilengineering.com/TurboCalcs.xls

[Homemade WRX]

here we go...
http://members.cox.net/drummerboy1784/turbosize.xls
now I just need to make maps for the GT12 and RHF3

[mangel83]

Hey Dan G, I was looking at that spreadsheet you posted but I have some doubts about it, hope you could enlighten me.

When calculating the turbine corrected flow you use Exhaust Manifold Pressure as 1.5*Boost (12psig), how do you come up with this value? does it represent a good approximation? But when you calculate turbine expansion ratio you use a slightly higher EMP (15psig) than before, is this just a mistake or..?? Also you use 1psig as turbine outlet pressure, another approximation?

[c5ho]

Perhaps someone could walk us through the entire process step by step with the equations used? I am personally still confused. Thanks.

[c5ho]

I've done some of the volume flow rate calculations for the compressor inlet and also for the engine at zero boost.

By definition, the volume flow rates required for the boosted situation will be higher than that of no boost at a given engine speed. However, where will this additional flow rate come from?

Thanks.

[VFR750R]

It will come through the restrictor until of course it is choked. With a turbo you may choke at 9000rpm instead of NA 12000 or so. The amount of air through the restrictor at choke will not change you'll just get there sooner.

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFR750R: The amount of air through the restrictor at choke will not change you'll just get there sooner. </div></BLOCKQUOTE>
exactly... a lot people who I discuss this with don't understand that...also that how fast you choke changes the lenght of your powerband (for the most part)...

[Dan G]

Manuel,

Unfortunately I've only clicked around that spreadsheet, I'm not familiar with it at all. I definitely didn't make it myself.

As for questions about assumptions/approximations, my best suggestion would be to actually build a turbo system to get those values experimentally. Then enter them into the equations, see the adjusted outputs, and iterate from there.

Also, I wanted to suggest this book to any teams that are just starting turbo research/development:

Street Turbocharging (http://tinyurl.com/mey3m)

This is a re-write/update to Hugh MacInnes' 1984 book "Turbochargers"�.Its not extremely technical, but covers the basic equations in relatively fine detail without skipping too many steps. Its also the newest book on the subject, which includes a decent amount of info not covered in Maximum Boost. Its a good read and only $13 shipped.

[golfer17]

im not so sure i understand fully what exactly it is your looking for, but i have been doing quite a bit of research on turbochargers for fsae myself, and here are a few threads ive found with what i thought was some helpful info.

http://fsae.com/eve/forums/a/tpc/f/125607348/m/14660271...466027104#1466027104 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/1466027104/r/1466027104#1466027104)

http://fsae.com/eve/forums/a/tpc/f/125607348/m/5946004534/p/1

as far as ICE fundamentals by heywood goes, my advisors in the automotive research program i am doing this summer have reccomended it as one of the best out there. i just recently purchased it on half.com for $44 or so (international softcopy ed.). ive been using it this summer for equations for calculating mass flow rates for sonic and subsonic compressible flows.

[c5ho]

Could anyone shed some light on the topic of turbine matching? I have figured out the compressor mapping side of things (I think) but am not sure what to do on the turbine side. I understand that I must relate the two using thw physical speed but how do I find the pressure ratio and mass flow across the turbine? Also, I understand that this mass flow across the turbine must also include the mass flow of fuel. How can I find that? Is the mass flow into the turbine simply the mass flow going through the engine (based on its displacement at various engine speeds)?

And, after all that, how can I calculate the power and torque of the engine with the turbocharger?

Thanks again for all the help!

[TPS]

Mass is a conserved property remember all that thermodynamics that you learnt. So unless you are releasing the exhaust gas from the engine someplace other than the exhaust.

Mass in= mass out
i.e. Mass fuel+Mass air= Mass out

[mangel83]

I have a few doubts about turbine operation, anyone care to point me in the right direction?

How do I determine turbine operating point (expansion ratio & corrected gas flow). Turbotwig (kirk) stated earlier in this thread (hint #3) "You need to figure out how much power is required to make X pressure ratio and Y mass flow (your compressor operating point). Then you need to figure out how much 'expansion ratio' is required on the turbine side to produce that power"

I do have the compressor operating point (PR, corrected air mass flow, efficiency, rpm) and the power needed to achive it, but how do I figure out expansion ratio needed if I don't know the efficiency of the turbine? Assuming it? (I guess for GT12 would be ok to assume 60% eff. and go from there, but what about GT 15V?)

The other thing I need is corrected gas flow mass, I have actual gas flow mass, and I have turbine inlet temp. but I need Turbine inlet pressure. Honestly I don't have a clue of what to do here. If I had expansion ratio and turbine discharge pressure I could find the inlet presure. Assuming I've figured expansion ratio in the previous step, would it be correct to assume a discharge pressure of say... 5% to 10% above atmospheric?

Is there anything I can do with rpm? After finding the compressor operating point, I have corrected rpm for both, compressor and turbine, and actual rpm of the system, but what can I do with this?

[pthickett]

We used a turbo last year, the restrictor does make it less useful, but useful none the less. However the fsae rules are being used that places the restrictor between the turbo and the engine, instead of straight off the throttle body. This means the turbo can draw more air in than previously, if that makes any sense.

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by pthickett:
We used a turbo last year, the restrictor does make it less useful, but useful none the less. However the fsae rules are being used that places the restrictor between the turbo and the engine, instead of straight off the throttle body. This means the turbo can draw more air in than previously, if that makes any sense. </div></BLOCKQUOTE>
They had turned down the proposed rule change. The restrictor is staying infront of the turbo.
Yes it does suck http://fsae.com/groupee_common/emoticons/icon_frown.gif

[BeaverGuy]

The rule change wasn't about the restrictor relative to the turbo but the restrictor relative to the throttle. Allowing the restrictor after the turbo would be rediculous as power levels would essentially be unregulated at that point.

[Kirk Feldkamp]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BeaverGuy:
The rule change wasn't about the restrictor relative to the turbo but the restrictor relative to the throttle. Allowing the restrictor after the turbo would be rediculous as power levels would essentially be unregulated at that point. </div></BLOCKQUOTE>

Thankfully someone can read around here.

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by turbotwig: Thankfully someone can read around here. </div></BLOCKQUOTE>
brainfart...meant TB...
I wanted to fool with antilag and a big plenum for fun...