Re: Burners.
For combustion to occur three things are needed, a fuel, oxygen and heat.
Combustion happens outside of the unit, where oxygen is present.
Taking a Trangia burner as a start.
The Trangia unit has what is essentially a double walled construction, with a well of fuel in the centre of the cylinder. The liquid fuel is free to flow by gravity into, and by capillarity up the void between the double walls. This void is packed IIRC with rockwool or similar, to act as a wick. The rim at the top of the double wall is perforated with a series of holes which act as jets. It is in the vicinity of these that the fuel burns.
Trangia recommend that the burner unit is not filled to the brim. The well of fuel is lit and this flame begins to heat the pan above it. More importantly, it heats the metal of the unit and makes the fuel inside the double wall to vaporise. This causes a huge increase in volume as the fuel boils, so the gas vents via the perforations. There is usually (until the burner has run out of liquid fuel) sufficient liquid in the burner to form a sufficient seal to prevent the vaporised meths from escaping downwards into the fuel well. As the vaporised fuel leaves the vents (so angled as to provide a broad heating area) it comes into contact with oxygen and is then able to ignite. It does not all ignite instantly so it is necessary to leave a space between the vent and the pan surface to allow sufficient oxygen to combine with the fuel. I believe that there is a design flaw with the Trangia unit in this respect- they often soot up the pans, indicating that incomplete combustion has occurred and carbon is deposited on the pan. I think that finer bore vents might help here, with the trade off of more frequent cleaning.
Associated with all of this is the fuel used. I’ve met people who ‘cut’ their meths with 40- 50% water to avoid smutting up. Likewise I have had almost soot free pans in Iceland burning the ‘brenstoff’ fuel available there. And it was amazingly cheap too; way cheaper than meths is in the UK.
Moving on to the Pop can burners.
They are IMHO often a poor second best to the Trangia unit. No sealing lid, no supporting lip, no ease of refilling. However, they have their place, not least the fun and satisfaction of building them and then using the fruits of one’s labour to cook with ?
Packing with Rockwool/ fibreglass to act as a wick helps. Pre- heating helps too. I think the lack of a central liquid filled (and thus air-tight) well to ensure a pressure differential may detract further from their performance.
Using a Caldera cone.
I’ve never used one but I am keen to try one out- can a jpeg be posted up somewhere? I like the idea behind it, it seems sound to me provided that sufficient oxygen is available easily enough so that incomplete combustion does not happen.
Additionally, I’m a great believer in the ‘low impact’, ‘take nothing but photographs, leave nothing but footprints’ approach. I prefer not to leave any sign of my passing at all. Cookers can and often do scorch the ground. Care needs to be taken not to allow this to happen, including placing hot objects onto the grass. The scorch marks remain for weeks or more showing where the grass has been killed ?
