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The other thing that occurred to me in reading
Dave's account is that he ran it on the ground, getting stable temperatures. It
was only after taking off, climbing to altitude, and then leveling off that he
had the temperature excursion and the problem.
** speculation/theory**
On the ground, the cooling from the prop blast
would be relatively low, therefore the glycol could circulate and warm up.
During climb -- engine generating a lot of power, air speed higher than taxi,
but still not at max flow of air through the radiators. Now you get to altitude,
level off, speed up, increase the flow of air (and resultant cooling) through
the radiator, and lower the power setting somewhat. ??Can you?? get into a
situation where the radiator is cooling the glycol so much that it gets viscous
and starts slowing down/blocking flow passages?? I don't know, but I had the
following observation on a cold morning in December:
I was driving my wife's PT-cruiser at steady speed
on an interstate with the temperature on the outside measuring -15*F. The
temperature gauge in the car would rise to the thermostat set point, hold for a
short time, and then drop off. This cycle repeated as long as I was maintaining
constant power input. When I would go off the Interstate, going through town at
~30mph, the temperature would stabilize at thermostat setting, solid as a rock.
My *hypothesis* of what was going on was:
1. At low speeds, the radiator/thermostat
combination could assume a steady state condition.
2. At highway speeds, the high rate of very cold
air flowing through the radiator would supercool the coolant, and when the
thermostat opened the cold coolant would cause the engine temperature to drop a
few degrees, then the thermostat would close and the temperature would slowly
climb back to the thermostat setting. I have watched for this behavior at less
extreme conditions, and if there it is not noticable.
Bill Schertz
KIS Cruiser # 4045
----- Original Message -----
Sent: Wednesday, February 01, 2006 7:49
PM
Subject: [FlyRotary] Re: Suitability of
NPG for Rotary Engine use
Thanks, Bill
Just thought it might be useful to some who might be
considering it why NPG just might not be well suited to the stock rotary
coolant system.
Yes, I noticed that the chart did not measure the
viscosity of the NPG at the same temps as they did the 50/50 mixture.
Might be a legitimate reason for that but escapes me. I suspect the
viscosity goes much higher at lower temps. No problem with a running
engine, but starting a really cold block might offer some problems as you
suggest. Especially given the small diameters of some of the GM cores
channels. Could be that Dave simply was not getting any significant
cooling due to minimal flow. I recall him saying the temps went up all
of a sudden and wonder if the coolant "trapped" in the block might not have
reached very high temps before managing to "burst" lose and send the temp
sensor soaring.
Ed
----- Original Message -----
Sent: Wednesday, February 01, 2006 6:40
PM
Subject: [FlyRotary] Re: Suitability of
NPG for Rotary Engine use
Excellent write-up Ed, I would be particularly
leery of NPG in a severely cold climate with small channels in the heat
exchanger. High viscosity and small channels can lead to high pressure drop
-- low flow. This then becomes unstable, if the flow becomes low, the fluid
in the radiator can become colder, leading to higher viscosity, lower flow,
higher pressure drop, all the while the engine portion can be
overheating.
Note that the viscosity for NPG+ is >10
times that of 50-50 EG/water at 50*F, a really interesting number would be
the viscosity at 0*F (Where Dave was flying). It could be that the pump
cannot generate enough pressure drop to force the fluid through the radiator
if it gets cold. On plain (room temperature) water, the Mazda pump can
generate ~20 psi at zero flow at 5500 rpm.
Bill Schertz
KIS Cruiser # 4045
----- Original Message -----
Sent: Wednesday, February 01, 2006
9:31 AM
Subject: [FlyRotary] Suitability of
NPG for Rotary Engine use
Things have been a little dull on the list, since
Dave reported on his "adventure".
Also, I recently received a phone call from a
rotary enthusiast (not on the list) about the use of Evans NPG (Propylene
Glycol) in rotary engines. I did a bit of research and my conclusion
was the rotary engine was not well suited to benefit from the
properties of NPG in its stock coolant system
configuration.
That the use of 100% glycol would
require increased coolant flow rates by 10-15% and more coolant
pump power would be required (hard to quantify this one but it appears in
the range of 15-25% more). Also the hazard of fire due to a leak on
hot exhaust would be increased (this would apply to a 100% mixture of
either Ethylene or Propylene glycol). There are benefits to using
NPG, however, in my opinion the effort needed to change the
rotary cooling configuration to safely use it makes the cost effectiveness
of the conversion questionable.
The apparent success of Evans NPG in reciprocating
engines is not in conflict with my assessment about its suitability for
the rotary engine.
Attached is some supporting (I believe) facts to
support this opinion (and that is all it is).
Ed
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