flyrotary@lancaironline.net Mailing List Archive

Georges, the 'wall paper' is back. I love cats but make it go away : )

OK, I'll give this a stab. But first an observation. I can't help laughing every time I read something on this thread because for the most part, everyone is right. It's just that everyone is right about a different part of the subject.

In terms of *continuous* power production, the rotary is limited by the number of BTU that can be dissipated through the combustion chamber walls. There is nothing (in common use) that can equal the heat dissipation ability of boiling water AS LONG AS IT DOES NOT PROGRESS TO FILM BOILING. The available data suggests that the rotary relies on nucleate boiling. This is not a simple subject so Google these terms if you are not familiar with them.

Because film boiling (or overt steam pockets, different subject) will result in skyrocketing combustion chamber wall temps (and a long term failure caused by cracking around the spark plug bosses in rotary engines), you might conclude that PG would solve the problem. And it might. It depends on the critical wall temperature that causes this failure mode (which I don't know). At the power level at which nucleate boiling occurs (about 170 continuous HP I think) PG use will cause higher wall temps than EG. That is the reason I am sticking with 50/50 EG & H2O.

This is a related subject to the oft belabored subject of water pump flow rates. If the flow rate is not high enough, nucleate boiling will quickly degenerate into film boiling.

From this point, the discussion could go off into innumerable permutations for which my beer befuddled brain is not prepared for this evening. I'd better wait to comment on the air cushion. Everybody is right on that too.

Tracy

Rusty

"boiling removes heat" I have a hard time understanding that quote. When racers started using PG they were able to run 15:1 compression on "pump" fuel

due to the fact that boiling coolant created hot spots in the combustion chambers & in turn causes pre-ignition (they also reversed the coolant flow direction to bring the cooled coolant to the hottest part of the system, & all this with no pressure cap. The one disadvantage I see in the 13b is that it can't handle the potential higher boiling point of PG. I have a 3.0 L V6 that I reversed the cooling system on to use in the Christavia (that was before I got hooked on the 13B)

Georges B.

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

From: Rotary motors in aircraft

Date: 06/27/05 12:13:55

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: NPG + use in aircraft??

Has anyone used the NPG+ coolant in an aircraft? What are the pros and cons?

NPG+ is standard issue in the 912S, and perhaps the 912 also.  If I'm not mistaken, Dave Leonard is running NPG+ now, and I'm running NPG-R.

The Evan's marketing folks can give you way more pros than I can think of, but I do think it's working very well. The primary benefit is the fact that it's native boiling point is in the 375F range, so you don't have to worry about a cascade effect of boil over if you unexpectedly run hot, lose pressure, etc. It's also not supposed to be subject to localized boiling around hot spots in the engine. Evan's claims this as a big benefit, but others, such as Tracy, think this boiling helps remove heat.  It's a bit more environmentally friendly too, so it won't hurt the rats in John's hanger.

The high boiling temp means that you don't need to run a pressurized system, which is my favorite part. There's less stress on the system, and any leak that occurs, will be much slower (initially) than if there was pressure.   I added an air separator tank, with a level sensor inside, so if I get a leak, I'll know about it before it gets to the level of the top of the engine. That was the best detection method I could think of.

The down side is the cost, and the fact that it doesn't transfer heat as effectively as traditional EG/water mix. Your temps will almost certainly go up some, but at least you won't boil over.

If the oil temp is below 180 F but the coolant is above 220F, is this detrimental to the 13B??

Define "above" :-)   I don't think there's anything harmful about 220F, or a bit over that for coolant, since cars do it all the time.  I believe the power will be reduced a bit at those temps though, and perhaps there will be more wear on the engine.  I've heard that, but can't say if it's significant, or even true.

Cheers,

Rusty

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