[killerbee]

this is the root of LLY cooling system problems. This is with a light load, on a normal Phoenix afternoon. I have had this number as high as 245.

At 245, and 20 psi of boost, at 5000 ft elevation the CAC offloads an additional 154,000 BTU/hr into the radiator. This is as much heat as is required to heat about 5 homes in North Dakota. Not to be too dramatic, the radiator is under attack.

 

[Bonediggley]

The dealer did some air box change, back last fall, when I brought mine in for running too hot when I pull my 5th wheel (over 210). It's been fine this winter and spring, but I'll towing here soon in the heat of the summer, see what happens. The fan runs all the time when towing, that's annoying. For some reason, it roars first thing in the morning too, stone cold.

 

[killerbee]

Even the new intakes are poor at reducing IAT, better, but still poor. 170 has been observed in the LBZ's.

The morning sickness is about par, unfortunately. The neighbors probably hate it as much as you do.

 

[chloeourdog]

Is there a bolt-on piece of plastic that outlines the wheel area (bolted to the fender - not the wheel well covering, but the outer trim itself) that could be modified with an inlet scoop to pressurize the inner fender area where a CAI draws air? In the picture below this would be the white painted area of plastic below the scoop area that was drawn.

 

[Thunderhead7]

I was on the recent Diesel Power Mag, that Banks is advertising a scoop for their CAI. It looks good, but I haven't seen one installed. Yes the fan is annoying!

 

[killerbee]

Is there a bolt-on piece of plastic that outlines the wheel area (bolted to the fender - not the wheel well covering, but the outer trim itself) that could be modified with an inlet scoop to pressurize the inner fender area where a CAI draws air? In the picture below this would be the white painted area of plastic below the scoop area that was drawn.

http://www.thedieselgarage.com/forums/attachment.php?attachmentid=10982&d=1178998530

do you mean a wheel well fairing that doubles as an intake scoop?


I have tested a couple of NACA scoop designs, and the best I have been able to obtain is 300 cfm. Using a leaf blower to simulate 50 mph flow

Not sure if it will be enough when the intake sucks down 800 cfm.

 

[killerbee]

I was on the recent Diesel Power Mag, that Banks is advertising a scoop for their CAI. It looks good, but I haven't seen one installed. Yes the fan is annoying!

I seldomly have morning sickness any more. The shrouds, CAI and EOC conspire to keep the clutch relatively cool on shutdown. That is where the cold start fan comes from...hot underhood temps on shutdown.

The tuning probably plays a part also. Using less boost at lower throttle settings means the CAC is staying cooler.

 

[fingers]

this is the root of LLY cooling system problems. This is with a light load, on a normal Phoenix afternoon. I have had this number as high as 245.

At 245, and 20 psi of boost, at 5000 ft elevation the CAC offloads an additional 154,000 BTU/hr into the radiator. This is as much heat as is required to heat about 5 homes in North Dakota. Not to be too dramatic, the radiator is under attack.

That is like 60 HP thermal KB. Your off a decimal place. It is more like 16,000- 17,000 BTU/hr. That's assuming a very efficient intercooler too. FWIW

 

[killerbee]

For the conditions posted, MAF is approximately 50 lb/min. The compressor is approximately 60% efficient at these higher IAT's. With a 245 IAT, or an increase of 150 over ambient, compressor discharge temps increase 250 degrees (150/.6).

The heat capacity, Cp, of this air is .25 BTU/lb, IIRC.

deltaQ=deltaT*Cp*m=250*.25*50=3125 BTU/min=187,000 BTU/hr (ADDITIONAL HEAT SUPPLIED TO THE CAC).

Now the CAC must reject 70-80% of this added heat, right in front of the radiator. The reamainder goes to hotter/thinner intake air. Presumably less power, especially considering that the stock code does not retard timing for these ignition hastening changes.

 

[fingers]

Hmmm, I was off on the decimal by your calcs. My bad I guess. So you are saying the turbo's turbine is generating 175 shaft HP? (40/60, 70 HP thermal/105 HP compression)

Theoretical HP to compress 350 ft3/min to 20 PSI gauge is <<30 HP.

 

[killerbee]

So you are saying the turbo's turbine is generating 175 shaft HP? (40/60, 70 HP thermal/105 HP compression)

Theoretical HP to compress 350 ft3/min to 20 PSI gauge is <<30 HP.

Ummm, no. All the work performed can be measured in the heat produced (adiabatic heating is a byproduct of compression, and no additional work is performed for this heat). You would take the adiabatic (reversible) portion and add it to the non-adiabatic, non-reversible waste heat produced,

OR just use the one process delta T. I have seen 170 degree air compressed to 500 F. This ends up as 250,000 BTU/hr or 98 HP work. That is for 800-900 cfm of 170 hot air intake. It is worse yet for 240 degree intake, over 300,000 BTU/hr. So, yes, non-adiabatic behavior results in more shaft HP. At 120,000 rpm, 98 HP is not unrealistic IMO.

But this 98 HP is not parasitic to wheel HP, at least not entirely. EGT's drop up to 500 degrees across the turbine, the exhaust firecracker "free snack" is serving up at least 2/3rds (guess) of that. Still, the cost of this problem, is parasitic HP loss (some) and high EGT, and of course...overheating. But not from high EGT as some people think. From a thermally overloaded stack, on fire at the CAC.

But if you agree at all, there is the explanation for the elusive drive pressure canundrum. I always thought that maybe drive pressure was related to the problems of the compression and airflow side, moreso than vane and exhaust related restriction. But who knows? I am planning a CAC tube swap to 3", whick according to some calculations, should remove 2-3 psi of restriction, translating to 2-3 psi less compressor discharge boost, or 10,000 rpm less. Too bad I don't have a drive pressure monitoring. It would be useful.

If this is something you can talk about more, please dust off the old test results from Wisconsin. If you can post a chart of the baseline run, and show ECT, IAT, Drive Pressure and EGT, I have made sense of something that we could never explain in those charts, re the ECT plateau, and the unexplainedsubsequent rise. I don't have the database, or I would do it myself.

 

[Turbotug]

If you're tapped for a pyro a drive pressure gauge wouldn't be too tough to do. Cheap boost gauge (extra), a couple feet of copper tube, a few more of poly tube, and a couple of minutes and you' re ready to rock. I might be free Saturday morning if you are looking for a hand.




On a side note, access to a metal lathe looks to be back on track. W/M by the end of the month maybe.?

 

[fingers]

Ummm, no. All the work performed can be measured in the heat produced (adiabatic heating is a byproduct of compression, and no additional work is performed for this heat). You would take the adiabatic (reversible) portion and add it to the non-adiabatic, non-reversible waste heat produced,


The Heating of the compressed air is a combination of both the adiabatic process and the efficiency of the turbo. Separate inputs, but both require power to generate.


OR just use the one process delta T. I have seen 170 degree air compressed to 500 F. This ends up as 250,000 BTU/hr or 98 HP work. That is for 800-900 cfm of 170 hot air intake. It is worse yet for 240 degree intake, over 300,000 BTU/hr. So, yes, non-adiabatic behavior results in more shaft HP. At 120,000 rpm, 98 HP is not unrealistic IMO.

To use this example: Assuming 5000 ft elevation (~12 PSI?) and 20 PSI boost

Adiabatic heating of the air charge would bring it from 170F to 372F. To get to 500F would require a turbo efficiency of about 60%. So that's 202F increase due to adiabatic and 128F due to efficiency.

At 3000 RPM that would be ~2880 lb/hr of air or ~67 HP to compress and another 35 HP dumped into heat. Total 102 shaft HP, close to you 98 HP. Total dumped out the CAC is 222,000 BTU/hr. A little less than your 250,000 BTU/h

But this 98 HP is not parasitic to wheel HP, at least not entirely. EGT's drop up to 500 degrees across the turbine, the exhaust firecracker "free snack" is serving up at least 2/3rds (guess) of that. Still, the cost of this problem, is parasitic HP loss (some) and high EGT, and of course...overheating. But not from high EGT as some people think. From a thermally overloaded stack, on fire at the CAC.

ALL of the work done by the compressor comes from the shaft and is at the mercy of the efficiencies of the turbine and exhaust system before and after it. Tap a turbo pre and post vane. Very enlightening.


But if you agree at all, there is the explanation for the elusive drive pressure canundrum. I always thought that maybe drive pressure was related to the problems of the compression and airflow side, moreso than vane and exhaust related restriction. But who knows? I am planning a CAC tube swap to 3", whick according to some calculations, should remove 2-3 psi of restriction, translating to 2-3 psi less compressor discharge boost, or 10,000 rpm less. Too bad I don't have a drive pressure monitoring. It would be useful.

If this is something you can talk about more, please dust off the old test results from Wisconsin. If you can post a chart of the baseline run, and show ECT, IAT, Drive Pressure and EGT, I have made sense of something that we could never explain in those charts, re the ECT plateau, and the unexplainedsubsequent rise. I don't have the database, or I would do it myself.

No, I'm done. Have a nice day.

 

[killerbee]

No, I'm done. Have a nice day.

:shrug:


If you look at a typical heatup curve of the truck, ECT, you see a gradual increase in ECT, then the fan comes on. When it does, ECT appears to plateau, and in some cases mildly reduce. As you continue under the same load, within 30-60 seconds of this plateau, ECT begins to rise again. It was a mystery, the fan seems to put out the fire, at least for a moment, then up she goes again.

If you look at what happens to IAT when the fan comes on, coupled with the thermodynamic changes of that moment, outlined in the above posts, an explanation surfaces. As soon as the fan comes on, IAT rises sharply.

As it does, the work performed by the compressor also begins to increase sharply, BECAUSE a dramatic decrease in compressor efficiency occurs, but also because higher compressor rpm is required for the same call for boost. Other stuff happens also, including higher air velocities of this "hotter" charge through the CAC and plumbing...this results in additional head losses, that must be compensated for to make the map sensor happy.

The worst thing that ever happened in the evolution of the truck, was the loss of the wastegate without a good software substitute for limiting work.

The result is this extra 100,000 BTU/hr or more of production in the compressor, and added CAC heat load. With more heat to dissipate, in front of the radiator, the ambient air heats up further, giving the radiator less cooling. (we have measured ambient air at 240 degrees post CAC, for the first third of the radiator...that air is heating the radiator, not cooling it) It takes 30-60 secs for the latency of this process to show up at the ECT sensor. In a short time, there is so much added heat, that the fan augmented airflow is no longer sufficient to curb it. Also important, as IAT increases with fan onset, the cycle begins that guarantees it will increase more, using the fan to connect the cycle.

 

[killerbee]

The Heating of the compressed air is a combination of both the adiabatic process and the efficiency of the turbo. Separate inputs, but both require power to generate.

agreed. And it makes compressor efficiency the center stage item to improve upon, IMO.

if the compressor were 100% efficient (adiabatic), there would be only the adiabatic heating, which is completely reversible, the air then behaving according to PV=nRT. If allowed to then expand, also adiabatically, then the air returns to the same temperature it started out as, yet no added work is performed by the consequential change in temperature

This is what happens across the turbine, as my understanding. Again, not 100% adiabatic. The combustion gases are piled up behind the turbine, by virtue of all this work that the compressor must do. A huge amount of backpressure, drive pressure. If the compressor were easy to drive, then this backpressure would be unloaded, and egt would drop significantly, also less parasitic losses.

Making the compressor easier to drive, is a matter of operating it in the most efficient way possible. That involves reducing IAT, using less restricive CAC plumbing, evaporative cooling, etc...AND incorporating a software "wastegate" for towing to limit the loop damage. All of it begins at the air intake, and fan coupled IAT increase.

 

[killerbee]

If you're tapped for a pyro a drive pressure gauge wouldn't be too tough to do.

Thanks for the offer, I have no way to log it.

 

[scootersparky]

New to the forum

Just wanna say thanks for all the great info.

 

[killerbee]

welcome!

By way of clarity, it should be stated, that for every 250 HP put to the ground, there is another 500 HP of thermal waste leaving the cylinders as hot exhaust. Easy enough for the turbine to use some of that.

 

[killerbee]

This Should Look Familiar

One of the charts that came from overheat testing 2 years ago. It shows 5 timed runs on a dyno, running under gradually increased load. Each run has some unique changes to the truck, not applicable to the topic here. It was never explained why ECT would stop rising when the fan came on, then continue rising a moment later.

I have illustrated the fan actuation. it looks the same in every run. Sudden rise in IAT. (on actual road tests, this precipitous rise is much more prominent, but this serves fine)

What happens is that the fan appears to curb the ECT rise, then it doesn't. The increased load a moment later is not enough to explain this. It is explained by the increase in turbo heat produced, due to the rise in IAT. Heat from the motor gets ingested into the turbo, where it is heated further by a factor of 150%. The heat is released by the CAC, and the hotter cooling air is no longer cool enough to serve the radiator.

Note: the lines on the bottom marked ambient, is room temperature.

 

[killerbee]

Death to the Radiator

This should make clear the meaning of "the radiator is under attack"