Ok, Al

 

That as you said, explains it.  My recollection of reported coolant temps were clearly in error and what you cited about coolant temps using NPG does correlate.  My mind is happy!

 

I have fortunately never experienced cascade boil-over and hope never to do so, clearly a terrifying and hopeless feeling to encounter why flying.  Shutting off the engine in such a situation might bring things back under control - if you have plenty of altitude.  But, I would assume most boil overs happen after a high powered takeoff on a hot day, so altitude may be lacking.

 

 I can certainly understand why that would induce someone to go to the NPG coolant. 

 

Long, Long ago and in a place far, far away - Japan to be exact.  Mazda provided that 180F coolant temps (out of the block) and 210F Oil temps (into the block) were the limits.  These can also be found in Racing Beat's technical catalog.   I have on occasion - and for very limited amounts of time - had oil temps as high as 230F and coolant as high as 250F.  These were cases where coolant was still flowing and pressurized.  After the first incident with an 86 N/A block, I found I had coolant "O" ring compromised (coolant leaking into combustion chamber), I then switched to the Teflon Enscapulate Silicon "O" rings and on the one or two occasions when the temps reached 220F oil and 230F coolant - there appeared to be no damage.

 

I believe that those limits were established for the mid 1980 era 13Bs and that block coolant galley improvements and casting changes (as well as use of higher temps rubber seals) have probably raised the permissible operating temperature.  But, I do not know of anyone who has tested an engine to destruction to find out {:>)

 

Ed

----- Original Message -----

From: al p wick

To: Rotary motors in aircraft

Sent: Saturday, February 04, 2006 9:32 PM

Subject: [FlyRotary] Re: NPG Coolant Temperature vs 50/50

The Egg guys no longer operate at the normal 200F when they install NPG. I don't recall the exact number, but they operate around 215F (cruise). Which explains most of your theoretical differences.

They gain a significant safety bonus in the boil over temp. That safety margin is what it's all about. At least from the risk perspective.

So by operating at a higher Delta T, they compensate for the reduced efficiency of the fluid.

 

I've heard you guys describe the importance of operating coolant around 185F or so? Are you sure of that limit? Is that just a recommended thing, or hard and fast limit. I'm always skeptical of stuff like that.

 

-al wick

 

 

On Sat, 4 Feb 2006 20:56:49 -0500 "Ed Anderson" <eanderson@carolina.rr.com> writes:

Hi Al,

 

Appreciate your (anybody else welcome also) views on one other thing that is still bothering me about the use of NPG. 

 

Given that NPG+ has a specific heat of 0.66 at 212F or  20% less than  the 0.82 for the 50/50 mixture and given that NPG+ is  approx 7% more dense than the 50/50 - then that for the same flowrate for both it would seem that NPG still has a 13% lesser overall capacity for heat transfer  (at the same temps 212F and flow rates).

 

Also assume that the engine is produce the same heat load (Q),lets take alook at what temperature we might see with NPG+ compared to the 50/50 solution.  We have from the oldie but goody Q = c*M*DeltaT the ability to solve for the temperature increase, DeltaT.

 

Delta T = Q/cM, now if the combined effects of c and m  provide 13% less heat transfer capability than the 50/50 mixture that would indicated that to carry away the same Q at the same flow rate, the delta T of NPG+ would need to increase by 13%.  So if I were getting 180F with the 50/50 for the same Q load (and flow rate) then with NPG+,  I would expect 180 *1.13 = 203F.  Yet, if I understood correct we have reports  that lesser temperatures results noted by users of NPG - this leaves me a bit puzzled.

 

If my assumption is correct thus far, then I am at a loss to understand the reports of lesser cooling temps when using NPG+, it would seem just the opposite would happen, that is - the coolant  temperature would increase. 

 

Now,  If the coolant temp with NPG+ actually does  remain  the same (or decreased) for the same Q and flow rate,  then it could indicate the engine heat load is not being carried away as well as with the 50/50.  IF the reports of lesser cooling temps occurs when switching to NPG+  are correct, then it would appear to me that the engine must then be operating under a higher heat load (i.e heat not being transfer to the radiators as effectively) .  This doesn't even take into consideration the possibly lesser flow rate of NPG+ for the same pump speed as the 50/50 due to its higher 3 times higher viscosity (at 212F). 

 

 Yes, I have no problem understanding that boil-over has been eliminated - but, is NPG actually cooling as well as coolant temps may lead one to believe? I mean with NPG, I could have a excessive block temperature and still not have boil-over - but my rotary engine would likely have suffered damage.

 

 What am I missing? Inquiring minds (even old ones) want to know {:>)

 

Ed A

 

 

-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
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