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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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