Returning to Eric’s “Could we attempt such a re-circulation of ESBIT off-gasses to get hotter combustion?” question and Jon’s response, and in specific relation to my custom 2L ASAHI beer can derived windscreen (earlier discussed and with photos; quite some pages ago):
My screen consists of the lower part of the can, has a domed bottom, angled transition from base to sidewall, and its inner diameter is such that an open Esbit tripod just fits in nicely, and the legs just rest on the bottom, with the rivet and tray just clearing and virtually resting on the dome.
I generally use either a half or full 4g tab, depending on conditions, with Evernew 400 Ti pot, with lid, and typically between 250 and 310 ml of premade coffee (not that thick). In my opinion, this works well because:
1. The windscreen and bottom are continuous (one-piece). Hence cool wind does not enter thru any space between cylindrical windscreen bottom and ground (e.g. when resting on rough ground, pebbles, vegetation). (This is a critique of the Evernew Ti windscreen, though certainly not a deal-breaker).
2. Apart from the front opening to allow the pot handle and sometimes lighting, there are NO openings in the sidewall (or the bottom). I suspect this is the major factor in this system’s effectiveness. Hence cool wind does not penetrate through the sidewall of the screen (only through the front opening).
3. The domed bottom and Esbit tripod raise the tray from ground level so that there is in effect an insulating air pocket under the dome.
4. The interior of the windscreen is reflective (though not highly so), so that some radiant heat from the flame and warming pot is reflected back into the system.
5. Most of the air flow into the flame area is through the vertical space between pot and windscreen (other than the relatively small part through the front opening).
6. This air gets preheated from the warming pot and the hot windscreen, so that by the time it reaches the flame area, it is hot.
This configuration allows the system to be used in very gusty conditions; the only problem then is initial lighting (normally I just use an ordinary Bic-type lighter), which is a pain. I hate Bic-type lighters. Once the tab is alight, I can forget about it, it is not going to go out, though I like to stir the coffee regularly.
An incidental advantage I’ve discovered is that the closed windscreen and tapered base mean it can be placed easily on uneven ground and vegetation, worked into pliant vegetation, and has proved safe in use (not setting fire to surrounding/underneath vegetation). For storage, the 400 pot sits nicely inside (having taken the tripod out), and the pot with lid readily contains all the accessories, including folding Swedish cup, fuel, spoon, tripod etc. The whole screen + pot + gear is then enclosed in plastic bag and (more recently) tidy Evernew “Ti 570 cup” zip-top neoprene case. Other than the conductive heat (too hot to touch), I even suspect I could brew up (in cold conditions) cradling the system in my lap – maybe nestled inside an old jacket (QED; I have that much confidence in it). Or maybe the heat from the top and maybe the fumes would be too much; and if I sneeze… (Don’t try this at home – or elsewhere).
The main disadvantage is that larger pots or frying pan can’t be used with the system, which was one of the reasons I moved to the Evernew Ti windscreen, Titrivet, tray, base disk system earlier mentioned; but I’m still exploring options.
The main improvements possible would be an insulating layer on the outside of the windscreen; custom detachable Ti wire hanging tensile tripod (I’ve used a proprietary enclosing hanging system occasionally); somehow flatten and depress the top of the base dome to provide an Esbit tray so the Esbit tripod is not needed and support the pot probably on wire network or Ti pegs penetrating the windscreen; and beefing up the reflectivity of the inner surface of the windscreen, so more heat is reflected back to the pot and flame.
.
