[AR] Re: Microgravity and combustion.
- From: Peter Fairbrother <peter@xxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sun, 4 Jul 2021 05:51:28 +0100
On 04/07/2021 02:32, Bruce Beck wrote:
At 1G the convection currents carry uncombusted material out of the wick
area as indicated by the yellow flames.
The yellow part of the flame is hot solid carbon particles, created by
pyrolysis of the wax into carbonaceous fragments of wax molecules which
then react with each other to form particles.
They give off light just because they are hot, about 1200C.
The carbon particles include joined-up six-membered rings, sheets like
graphene, amorphous carbon, graphite, buckyballs and ... millions of
tiny diamonds.
Really :)
In microgravity the fuel can't
escape before complete combustion as indicated by the blue flame,almost
no convection currents.
The blue colour is chemiluminescence, where the reaction of the wax
vapour and air gives off light.
Combustion is pretty total, but because the influx of air is limited to
diffusion not convection-and-mixing the rate of combustion and thus the
temperature is too low for pyrolysis to break up the wax molecules
except in the outer flame itself, where there is plenty of oxygen to
burn up the fragments before they can agglutinate into solid particles.
Typically the temperature is also too low to maintain the flow of wax
vapour from the wick, and the candle goes out.
I think it may be possible to make a candle which burns indefinitely in
zero gravity, but I don't know whether anyone has done it.
Peter Fairbrother
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