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  #46  
Old 11-07-2005, 11:12 PM
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StRaNgEdAyS StRaNgEdAyS is offline
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Default On Intercoolers.

I used to have a motorcycle that was strictly for the insane, an 1100cc turbo fuel injected suzuki with a T04.
I had trouble when it came to fitting an intercooler, I did not have enough room for an air-air intercooler, and with no liquid cooling system an air-liquid one was not feasable, so I designed and built with the help of a friend who was fridgy mech an air-gas system using the salvaged parts of a portable car refrigerator.
This was a pretty simple device where a small core was made to fit into a modified air intake system (Think a car air con system) and the fairly small and thin radiator was placed up front near oil cooler. The compressor was run from the electrical system, it did not weigh much, I could hold the entire system with one hand without getting a sore arm (no it did not fit into my hand) and it did fit in without any major modifications, and absolutely no structural mods to the bike's frame.
One thing became apparent pretty quick and that was that if the enigne was left to idle with the sysyem running, the intake would ice up espescially in humid weather, so a pressure switch was added to only turn it on once boost was being produced.
Don't know how this would go for you, but it's a thought.
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  #47  
Old 11-08-2005, 09:52 AM
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I'm sure the system will not be as dificult as i am thinking - the current turbo that is on the plane and was in both the front and back position on a 337 worked with full power to 18000 and was designed in 1965!

337's are notorious for poor cooling on the rear engine. i only wamt an extra 7000 feet of full power
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  #48  
Old 03-12-2006, 11:12 PM
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MMMMMM - at 9:30 this morning I started to get into the calcs for the turbo in earnest.. mplafleur has done some great work on a spreadsheet, rv6jguy has had some great input...but, i feel i need to understand all the calcs.

All of em.

So i started simple - i new i needed formulas for F to C to K and for lbs burned per minute and for altitude density. and on and on and on.

So i just started doin it, stealing formulas for lafleur's spreadsheet, findin more on the internet. things were sometimes makin sense and sometimes NOT.

Here is one that is not. Turbocharger is about 75% efficient. MMMMM most formulas take the temp gain and divide it by the 75% to get a new temp gain. To me it does not make any sense

I went to the garret PDF i downloaded a long time ago - their formula does not do that for PR.

seems to me that is in error as the .75 says, to me, that of the exhaust gas energy that is present - it will create 75% of the power of a "perfect" turbo.

The garrett formula does not do this.

it is 11:08 PM, i been on this for a long time, a little at a time - do the formulas and then ponder them, and then do the formulas and ponder them again.

The more i do them the more it appears that i will easily get full power to 25000, but time will tell.

garret make the "maps" for their turbos - they might have the temp gain figured in so that you do not need to take the extra volume created into consideration. don't know

but by the time i am done - i will - ifin it causes me to lose the rest of my hair
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  #49  
Old 03-13-2006, 01:55 PM
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The modern Garrett will maintain your 31 inches to 25,000 feet no problem if your engine, oil and inter cooling systems can dissipate the heat. This is a fairly tall order to do with low drag.

Matching should involve considerations of compressor surge at high altitude and lower power settings, overspeed (not a concern in your case) and peak efficiency at typical cruise altitudes and power settings. This can be a bit more sticky if you cruise sometimes at 8000 and sometimes at 25,000.

It is easier in my view to use in hg Ab and degrees R for the calcs. Calculate massflow for the ambient temperature and pressure at various altitudes. I use hp divided by 8.07 for massflow in lbs. min. Cross pressure ratio with density ratio at your given compressor efficiency. Multiply density ratio with the calculated mass flow to arrive at compressor inlet airflow and correct for absolute temp (R). Plot this point on the map and do all your others including SL takeoff power. Anything below 65% is not good unless it is the SL WOT rating where compressor discharge temps won't be too high anyway. Any point near the surge line is a no no.

By the way, compressor discharge temps are always higher than calculated due to conduction through the bearing housing.

Have I helped or hindered?
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  #50  
Old 03-13-2006, 02:11 PM
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Thanks RV - I will eat this tonight, one more bite at a time. right now i get a P/r of somewhere between 1.6 and 2.95 - heh heh heh - anything below 2.3 looks GREAT.

understand the heat issue, but don't yet know how to calc it appropriately yet. funny - the factor all the calcs use is for CO2

I know what i have is decades old and worked in the front and back of a 337 - the 337 back was notoriously bad on cooling, it made full power to 18000 and then down the same way you would go if N/a at sea level to 7,000 on the power from 18000 to 25000

the intercooler that i have on the engine now is quite small, my plan is for about 3 times as much from a sq inch, nit cubic inch standpoint, have the room in the wing root with p51's style scoops.

If i can't beat the cooling of the 337 back or front engine position - I'll eat my 10 gallon resistall, wife won't let me wear it anyways
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  #51  
Old 03-13-2006, 02:32 PM
Lynn Erickson Lynn Erickson is offline
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Thanks RV6EJGUY, Dust, did that make sense to you? Ii does now that I read it like 5 times. I have been learning more and more about turbos from this forum. keep it up. starting to think turbo again but just don't know where to put it.
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  #52  
Old 03-13-2006, 02:40 PM
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Quote:
Originally Posted by Lynn Erickson
but just don't know where to put it.
In the boat tail, well shielded for all three types of heat transfer - you could feed it combustion and cooling air from the naca (spell checker says nacho)
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dust

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  #53  
Old 03-13-2006, 05:54 PM
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The compressor discharge temp will be pretty high at 25,000 feet you should try to keep the intercooler discharge temps below 160F to be safe from pre-ignition. This involves a pretty large inlet as the massflow available is less than half what you have at SL. Ditto for the heads, oil cooler etc.

If you give me your power settings at various altitudes, I'd be happy to run the calcs and see what I come up with.
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  #54  
Old 03-13-2006, 07:45 PM
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Quote:
Originally Posted by rv6ejguy
By the way, compressor discharge temps are always higher than calculated due to conduction through the bearing housing.

Have I helped or hindered?
You wanna laugh - it may be, just may be that the temps are also off cause someone used the wrong gas compression factor. everyone uses CO2 as a representative gas for its compression heating factor. Well, i can understand the air picking up some temp as it goes through the compressor, but, think of it, if it was THAT easy to heat air that is going buy really quickly on surfaces that are not designed to be heat transfer surfaces then the intercoolers would work a lot better than they do.

I'm gonna bump up all temps by 20%, when i finish the calcs, we can compare.

I am also gonna contact garrett on the method they produce the MAPS cause their calcs do not take temp increase into consideration, maybe they make the MAPS to match their computations and not what we all think they should be calculated

that make any sense?
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  #55  
Old 03-13-2006, 08:16 PM
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Strike that last 20% comment - how much do you see the temps go up over the calculated value?
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dust

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  #56  
Old 03-13-2006, 11:24 PM
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When turbocharger compressor maps are generated, they use electric motors to spin them up, not exhaust. So no heat conduction into the backplate. Temperature measurement is actually how compressor efficiency is arrived at. In the real world we see CDTs as much as 45C over calculated values. This is highly dependent on compressor massflow. At idle for instance, if you wait long enough, CDTs can reach over 70C with the compressor barely spinning, PR zero. This is strictly due to conduction. Spin up the compressor up to 20K and within a minute CDTs drop 40+C as all this air cools down the backplate and compressor housing.

In flight I've seen 110C CDT in the climb at 35 inches and 10,000 feet. You can guess this will easily reach 200C+ at 25,000 feet. With that turbine housing glowing red hot 2 inches away from the backplate, the IR flux is tremendous.

The Exxon Tiger was running 1800F EGT, 525F CHT, 260F OT and 400F CDT at 47,000 feet. OAT was -70F! CDT temp rise 470F!
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  #57  
Old 03-14-2006, 10:05 AM
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Did not dig into it last night, everything in my house has broken since christmas

Started with oven, 180F tap, kitchen faucet, sump pump AND backup sump pump on SAME weekend. Note, it was the weekend that my 2 grand daughters daughter and son in law, daughter and her wife, Son and his girl friend. were in town for the holidays. Next it was a TV, then another TV, then the washing machine and yesterday the pump up to the septic field.

My son drove down 2 1/2 hours and fixed it. For some reason i thought replacing the pump so that all of the septic discharge went into the septic field instead of the yard took precedence over turbo calcs.
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  #58  
Old 03-14-2006, 12:00 PM
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Sounds like an incoming power problem
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  #59  
Old 03-14-2006, 12:53 PM
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Quote:
Originally Posted by rv6ejguy
Temperature measurement is actually how compressor efficiency is arrived at.
So by this you are saying that they compute the turbo outlet pressure that should occur and then measure what actually does occur and that differential it the efficiency.

So i have to divide the computed outlet pressure by the efficiency (say 75%) to get the actual computed output temp AND then add for conduction from the hot turbo side.
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dust

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  #60  
Old 03-14-2006, 04:57 PM
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They measure the pressure ratio and compute ideal (theoretical) temp rise at 100% efficiency and compare this to the actual measured temperature. The difference is the compressor efficiency. This is something you don't really need to know as they have plotted airflow vs. pressure ratio vs. compressor efficiency vs. N1 for you on the map already.

Using a VE figure pulled out of a hat is far less accurate than using hp to do the calcs. If we assume an AFR of 13 to 1 and a BMSFC of .5 at this AFR, let's see what we come up with. 200hp, 100 lbs. of fuel per hour, 1300 lbs. of air per hour. Divide 1300 by 60 for lbs. per minute equals 22 lbs./ min. This is fairly close (24.8) to my standard figure of hp divided by 8.07 will equal mass flow in lbs./min.
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