flyrotary@lancaironline.net Mailing List Archive

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.

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

From: William

To: Rotary motors in aircraft

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 -----

From: Ed Anderson

To: Rotary motors in aircraft

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

Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

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