[Stoves] RE: Henson Center Fiure Burner System; Was: Re: improving charcoal stoves

[Crispin Pemberton-Pigott]

Dear William

I think you are on the right track here.

>A while back, I played with altering a MIDGE with a hardware cloth  
>cone in the center.   The idea was that the hot wire would help to  
>push the ignition of the CO.

Unlike a spark plug which must fire at a certain time, the flame is always required so it will be better in principle to have a continuous ignition source such as a hot wire.

The best way to get your hands on a reasonable piece of wire is to go to any engineering shop that welds stainless steel and ask them to sell you a length of stainless steel MIG wire.  This is available in a number of diameters.  I happen to use 1.2mm.  It comes in 17 kg rolls.  They can reel you off 20 metres or so.

Don't be impressed by the remarkable stiffness.  It is hard-drawn so it will soften after heating to a high temperature.  You can soften it by passing it through a flame before use or else use it as is and it will soften later when fired.

If you find 309 MIG wire it is cheap(er) and takes 750 deg. well.  By that I mean it can run for hours and hours at that temperature in the presence of oxygen.

It will be sold by the kilo so it is far cheaper than buying 'stainless steel wire' from a craft shop or hardware store.

The largest diameter people will keep is probably 2.2mm.

As the wire conducts heat at about 1/2 the rate of mild steel, it tends to remain hot for twice as long, meaning you will see it glow brightly for twice as long after a flame has been on it.  The CO gas tends to get pushed around by the random motion of the fire so your chances of getting it lit are better when the wire stays hotter longer.

The larger the wire diameter, the more heat is stored and the more expensive it is, and the longer it will last.

Inconel and nichrome wire is also available (www.kanthal.com ?) but these products are made either from 'unaffordium' or 'unobtanium'.

The total area of the wires in the gas path (what some would call 'coverage' or 'density') starts to become important when there is a great deal of wire.  Without exploring the limits, I found that 10% coverage does not interfere with gas flow and gives reliable ingition in the Vesto downdraft coal stove. That means a 1.2mm wire at a 12mm spacing.

Happy flaming!
Crispin