[Stoves] Oversized stoves / thermal insulation

ajheggie at gmail.com ajheggie at gmail.com
Mon Nov 8 17:06:02 CST 2010


On Monday 08 November 2010 04:21:05 Crispin Pemberton-Pigott wrote:

>
> What I observe is that the time (temperature and turbulence having been
> taken care of) is dominated by the need to break down the C+ radicals
> that are probably forming in the flame as the Hydrogen breaks away.

It could be that the higher C components cracked off from the vapour have 
characteristics that make themselves less ignitable than if sufficient 
oxygen had been present intially, i.e sufficient premixing took place 
before ignition.

> Back to 65mm - very good. Cheap and nasty construction and still had a
> CO(EF) below 200 with ease. CO/CO2 reached 0.07% and sat there. That
> was in March '10. The length of the burn at say 9 kW was about 500mm or
> so. As that is not containable in a standard stove, it pretty much
> demands a new layout. In SA we got a shorter version working very well
> with a 50mm diameter but for 5.5 kW (meaning about 1/2 the gas volume).
> More about that in a few weeks.

It looks like developments in pellet stoves are moving away from the "burn 
pot" toward "blast tubes" but it looks like empirical results like yours 
will rule for our simple stoves.

> >If the combustion chamber is better insulated and can re radiate heat
> > back
>
> to the flame then I
>
> >would expect  the flame length to increase as these PICs contribute
> > their
>
> heat and continue burning.
>
> Mmmm....well if the heat is kept in the flame is shortened - all the
> required air is present in the mix for the whole time.

Yes but I was meaning the dirty sooty flame would lengthen because the 
soot would add its fuel. I'm surmising that given the correct air supply 
even though the flame would be sooty for a given fuel massflow ( because 
the flame length allows insufficient time for the soot to burn out) then 
enclosing it with a hot tube will allow soot to burn out.

> >I'm guessing there's a bit of a corollary with the lamp test that Tom
> > Reed
>
> told us about for
>
> >establishing the detonation point of a hydrocarbon by the maximum
> > flame
>
> length
>
> What does he mean by the detonation point?

It was my word, not his, it is more properly called the autoignition 
point, but in automobiles it it this that determines whether the mixture 
burns smoothly or detonates above the piston (pinking). In petrol engines 
one wants a fuel with a high autoignition temperature, so it doesn't 
start burning before the spark. With diesels you want one with a low 
autoignition point, so it starts burning as soon as it hits the hot air.

A good diesel fuel will apparently have a short diffuse flame before it 
becomes sooty, petrol longer and meths longer still.

AJH




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