Bill The reason that PG is use in automotive cooling system is to reduce "film" boiling. Georges B.    -------Original Message-------   From: Rotary motors in aircraft Date: 06/28/05 08:39:14 To: Rotary motors in aircraft Subject: [FlyRotary] Re: NPG + use in aircraft??   At 11:58 PM 6/27/2005, you wrote: >  Al >What I meant was due to the high boiling point of PG it would protect >against"film" boiling which causes pre-ignition.            I don't think so.            The higher boiling point would raise the temperature of the hot spot. This is not likely to impede film boiling. It takes a fairly stout heat source (and a big temperature difference) to get film boiling in plain water. Raising the boiling point would only make a difference if you were very close to the transition and everything else stayed the same.            The higher viscosity of NPG would tend to impede convective cooling (as well as forced convection) which would promote localized film boiling. The lower specific heat and heat of vaporization for NPG would make it much more prone to film boiling as well.            Looking at the numbers, it seems to me that if you have film boiling problem using water, you are going to be much worse off using NPG.              Bill Dube'     >>  Homepage:  http://www.flyrotary.com/ >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html .