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From: rmartin@clear.com (Bob Martin)
Newsgroups: sci.space
Subject: Re: Fire in Space
Message-ID: <1991Feb1.225031.8293@clear.com>
Date: 1 Feb 91 22:50:31 GMT
References: <7332@crash.cts.com>
Organization: Clear Communications, Inc.
Lines: 81

In article <7332@crash.cts.com> dang@crash.cts.com (Dan Gookin) writes:
>
>I have this perverse curiosity about what fire--specifically a
>flame--would look like in space.
>
>If figure if you lit a match, it probably would lack the familiar
>conical shape the flame has here on earth. In fact, I think it would
>look like a point of light or perhaps a spherical flame.  (And
>then my mind thought "Ooops, pure oxygen atmosphere--Whoosh!)
>
>But what would fire look like in space? or actually, zero-g? Would
>there be flames? Would it be spotty and amorphous? There is no
>scientific reason behind this; just curiosity (a mind-exercise,
>if you will).
>
>dang  

This is a mind-exercise that I find rather tantalizing... 

First of all, what is a flame?  A flame is a stream of incandescent particles
and gasses.  The incandescense is due to the heat produced by the oxygen-fuel
reaction.  The shape of the flame is due the the fact that the hot gases are
less dense and thus rise away from the source of heat. (convection).  
This creates a current of fresh oxygenated air flowing past the zone of
reaction allowing the reaction to continue as long as their is fuel.

Without gravity (or a suitable substitute such as linear acceleration
or angular momentum) there would be no reason for the hot gases surrounding
the reaction zone to move out of the reaction zone.  Thus the only way that
oxygen could get to the site of the reaction is diffusion, and this would
seem a very slow method indeed.  probably the reaction would proceed so
slowly that the reaction site would cool to below ignition temperatures
and the reaction would cease altogether. 

In short there would be no sustained flame at all (except on the net ;-)
and a very brief flash of incandescense.

However, what if you blew on it!  You could keep your match burning by
constantly blowing on it with a gentle stream of air.  Or by waving it
around in a gentle manner.  Stop for an instant and the flame might go out.
(This seems like an interesting ploy for a sci-fi short).

Flames could exist in a ventilated area as long as the air was moving
at a rate sufficent to keep the reaction site from cooling down too much.

Also it seems likely that you could create a small airflow by attracting
the ions created near the reaction zone with an electrostatic charge.  Thus
you might be able to keep the flame buring by placing it between two charged
plates.  The flame would point at the plate which was attracting the most
ions.  If you decrease the voltage on the plates the airflow would diminish
and the flame would get smaller.  Increase the voltage and the flame becomes
bigger.  !!Electrically controlled fire!!

On a rotating space station, convection currents would be generated by
the centripetal force normal to the floor of the station.  But they would
also suffer corriolos (sp) effects.  So flames would burn pointing more or less
towards the hub of the station, but a large enough flame would exhibit a 
curious curve in the direction of rotation.

A thin flamable thread might be able to burn even in the abscense of any
airflow because the reaction site would travel along the thread quickly
enough for it to reach sufficient oxygen to keep the temperature of the
reaction site high enough.  Similarily a very thin sheet of paper might
exhibit the same effect.  In the case of the thread, the "flame" might
appear as a small globe of incandescing gases moving along the thread.
In the case of the sheet of paper it might appear somewhat cylindrical
bending and turning as if made inroads into the fuel.

A bunsen burner would probably burn well, since the flow of gases out of
the burner would stir the local air up enough.  The same is probably true
of a conventional gas stove, or a butane cigarette lighter.

-------

I wonder if any experiments of this nature have been tried on board
the zero-gee aircraft????
-- 
+-Robert C. Martin-----+:RRR:::CCC:M:::::M:| Nobody is responsible for |
| rmartin@clear.com    |:R::R:C::::M:M:M:M:| my words but me.  I want  |
| uunet!clrcom!rmartin |:RRR::C::::M::M::M:| all the credit, and all   |
+----------------------+:R::R::CCC:M:::::M:| the blame.  So there.     |