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At 08:57 AM 6/29/2005, you wrote:
Bill
The reason that PG is use in automotive cooling system is to reduce "film" boiling.
Georges B.
It may be marketed that way, but, given the numbers, the heat transfer equations tend to disagree with that claim, at least for the case of film boiling on a local "hot spot".
You can choose specific instances that would stop film boiling by switching from water to NPG. For example, if a large portion of the engine was getting quite hot (like the heads) NPG could help. The heat source is diffuse and not high temperature. This would be where the heat source was only modestly greater than the boiling point of NPG.
In the case of the localized high temperature area around the spark plugs in a rotary, I don't think that NPG would help. Perhaps I am missing some key point.
The way to find out would be to take a thermal image of an engine on a test stand, with water and then with NPG. Alternatively, you could use thermocouples or an IR pyrometer.
Bill Dube'
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