Date:         Sun, 5 Dec 2010 09:03:22 -0600
Reply-To:     mcneely4@COX.NET
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dave Mcneely <mcneely4@COX.NET>
Subject:      Re: Vanagon engine fire or mishap in Roanoke, Va
Comments: To: Mike S <mikes@FLATSURFACE.COM>
In-Reply-To:  <20101205125453.1E89BA0005@locke.alientech.net>
Content-Type: text/plain; charset=utf-8

---- Mike S <mikes@FLATSURFACE.COM> wrote:
> At 07:38 PM 12/4/2010, David Beierl wrote...
> >  unless gasoline
> >behaves differently than it used to (and it might -- it's more of a
> >mixture of heavy and light components than when I was young) you can
> >spray it on a hot exhaust pipe without it catching fire* (whereas of
> >course a small spark will ignite gasoline vapor).  Oil, OTOH, dropped
> >on a hot exhaust will burn.
>
> Do you have a source for that? Common sense says it's wrong, and
> according to this web site:
> http://www.tcforensic.com.au/docs/article10.html#1.1 , the ignition
> temperature of gasoline is lower than that of motor oil (257C vs.
> 260++). Gasoline is also much more volatile, making explosive
> combustion more likely.

Perversely, it is the high volatility of gasoline in this situation that prevents the flame up, at least according to a physical organic chemist I once knew.  He claimed that when the amount of gasoline was relatively small and ventilation was good, the vapors formed quickly and wafted away before ignition could occur.  Of course, his day job was developing the stuff that makes disposable diapers, menstrual pads, and so on absorbent.  It is likely that right at the hot surface, little or no fuel is present, and only inches away the temperature is below ignition point.  Oil remains on the surface to be heated and ignited.

Seems to me that our only list chemist is Alistair, whose expertise seems to be more in the line of microbial work.  But being a good scientist, he might have some insight.  Alistair?

As I said before, I am not willing to perform the test except with such a small amount of fuel that I might not consider it representative of real world conditions.

--
David McNeely