My Pocket Charcoal Chimney

Yeehar! I think I’ve finally cracked it! The weeks of thinking and design and testing and buying and taking back to the shop and nearly setting the house on fire are finally over! Not only that, I think I may have just broken new ground in the hotly-contested (ouch, sorry) field of backpacker’s lightweight camping stove. Probably not, but my first hour or so googling and youtubing didn’t turn up anyone else doing what I just did this afternoon. One or two doing it badly, of course, and one very nice man making a tediously long pig’s ear of it, but…

It’s a good job I had a success today, because I was getting pissed off with the whole affair.

Over the last few weeks I tried making a simple wood stove and a gassifier (wood-gas burning) stove. Not content with those, I bought a new “ultralight” propane/butane burner, and then I returned it because with a decent tin of gas it was almost as heavy as my current gas stove, I stripped the heavier bits of metalwork off my current stove, a Rapijet, which has been a pain in the neck since I bought it, but I thought better the devil you know. Wrong. Shit devil I know.

I experimented with alcohol stoves and considered hexamine solid fuel (but I’ve used that before and knew it wasn’t for me). The last thing but one that I tried was cooking by candle power, a tea light (albeit with a lot more wicks), but hot burning molten wax is hardly any less scary than hot burning alcohol (in fact probably a lot scarier) and tends to make a load of soot and smoke.

Don't do this.

Er, don’t do this…at least not without lots of safety precautions.

After the candle incident, I thought I’d have to put up with the Rapijet and forget home-made ones. I filled it again, but it started hissing out of the valve at the back, which is some kind of adjuster – maybe it’s meant to release pressure and is factory set, and maybe I moved it while I was stripping it of superfluous ironmongery – and then all I seemed to get from it was a very low flame or, if I unscrewed the adjuster a little, the adjuster itself would flash over and squirt burning gas out the wrong bit. It was the last straw with this thing, which let me down when I first used it on a cold wet night due to the cheap plastic knob rotating on its spindle, which was jammed off.

Back to the drawing board. Of course, there’s nothing wrong with many of the traditional camper’s favourite fuels and stove types. They have different strengths and weaknesses in different modes of use. Camping by car with my partner, which I do most years once or twice, I want to put a table up with twin gas burners on it and slap in a cheap can of whatever-ane with which to produce my gourmet, al-fresco feasts. But for my other camping…

My other camping is solo wild camping, not that I’ve done much of it: it’s mostly in my head, to be honest. I spend most of the winter wishing it was nice weather to camp, and then when the summer comes I start designing and making stuff and don’t get out much! Very bad. I’m hoping “my new invention” will encourage me to get more trips in this year.

Should I tell you, though? Should I divulge the secret? Should I develop the product, create a brand, manufacture it by hand in my shed? Dragon’s Den? Nah. I’m only joking. It’s not all that revolutionary – the secret is just…wait for it…

burn charcoal

…briquette or otherwise…but…

crushed or broken

(sorry, yes, that really is it!).

On the other hand, it’s like doh? – wtf? – why is nobody doing this? Why are people lugging around bottles and cans of petro-chemicals? Why do they put up with the smell of fishy parafin or choke on their “smokeless” woodgas stove for ten minutes while it “gets going”?

I think a stove could be designed, and charcoal products developed, to make a wonderful backpacker stove, quick, easy, hot, pretty clean burning, pretty predictable in output, lightweight and cheap, for those who aren’t interested in knocking one up from old bean tins and smashing briquettes with a hammer. And it might just be me.

Bean there, done that...

Woodgas, yeah, right on.

Why is charcoal better than wood, even in a woodgas stove? Because when you burn wood it produces a lot of gases that take some of the combustion heat to create, and you have to evaporate any remaining water even in wood that seems bone dry. The hydrogen in the carbohydrates becomes water when it combines with oxygen. Charcoal – which is produced by partially burning wood in an oxygen-depleted environment – is almost pure carbon, so it burns hotter and, given enough air, completely smokelessly as CO2 (which is “green”, “carbon-neutral” CO2, in that it comes from a non-fossil fuel). It doesn’t have to deal with all the water and other gases being produced. Woodgas burning is fine on a larger scale – I just don’t think it scales down to a backpacking stove that well. A lot of woodgas stoves are ideal for producing charcoal, and maybe I didn’t have the best woodgas stove ever, but it blackened my pans rotten, as everyone says they do. They swear blind they’re burning “clean”, burning the smoke, but that soot on the pans is unburnt carbon, char, charcoal. Go figure.

My first experimental burn of a briquette in a bean can was rubbish, but the second, with a broken/crushed charcoal briquette (just one) was a revelation. In 15 minutes I was enjoying my coffee and wondering how much more cold water I could boil on the remaining fuel that was glowing in the tin. The first boil was about 250 ml (sorry me no speaky american – it’s a decent mugful). The same amount of water from room temperature only got up to about 65 Celcius (too hot to hold) but didn’t boil.

If you try burning one charcoal briquette in a tin, it’s hard work getting it going and it easily goes out.

I haven’t weighed this stuff, but it’s light. It’s charcoal, see? At least it mostly is. Briquettes have other ingredients (which some people make a fuss about, but really without much of an argument IMHO), but they’re still almost pure carbon. Or if you prefer, use natural charcoal, which I haven’t tried yet, but should work too. In fact, I can’t wait to try it. [Edit: actually, I got a shock to find they’re heavier than I thought – about 50 or 60 g., but I reckon with some tweaks I can improve efficiency a lot yet.]

So anyway, here’s a few photos of the burn, and a video follows. This time I put a small piece of firelighter (more than necessary, by the way) in the base of my stove – which was designed really as a simple wood burning stove, so the big door is actually not that useful here.

Then I inserted three wire bars across and the grate that rests on it (old computer fan grill) and dropped the crushed briquette onto it, with the powdery stuff falling last onto the larger pieces.

On lighting the firelighter there was a lot of smoke at first. I thought this was another of my famously bad ideas. I grabbed my camera to document the dire failure that was developing before my eyes. The video shows the last second of smoking just before it got to flash point and from then on there was hardly a wisp. I don’t remember exactly how long it smoked, maybe 30 seconds. [Edit: and I’ve found that most of this can be avoided too by putting another small piece of lit firelighter on top, which ignites the exhaust gases and smoke until the charcoal gets hot enough to do that itself.]

Next, flame poured out the top, and I put my can on top of the stove on wires, although I knew that with charcoal you should really wait until they’re glowing embers – I was pretty desperate for a coffee by this time so didn’t want to waste the heat.

As the flames died down a little I was able to add the second can on top of the wires, which acts as a chimney and insulation for the top part of the kettle (which is just a beer can with a lid). Putting too many obstacles in the way can choke a fire, but this coped pretty well. I have to say that I was still being very impatient, and an even better burn and boil would have resulted from waiting longer (as the 65 degree refill shows). I was so anxious to grab every calorie from the stuff that as it died down to glowing embers completely I couldn’t be bothered to mess about putting the wires through the holes in the side of the can to support the kettle just above the coals: instead I just lowered it right onto the fuel.

Kettle sitting directly on charcoal right inside chimney, with windbreak rolled up round base for extra cozy.

The photo at the top of the article shows the condition of the charcoal on removing the kettle of boiling water. I put another brew on and began adding insulating foil and cozying it all up even more. I’ve not had any experience of burning charcoal before – I don’t even do BBQs – so I’m not sure how best to balance the airflow/insulation, but once embers are red hot it’s sensible to close things down a fair bit. I expect my chimney design will help draw air in at the bottom, and then the heat of the exhaust gaes has to hug the kettle all the way up the sides. (The second can isn’t part of the backpacking stove design, as they don’t pack up small – instead I have a wire mesh and foil extension to do the same thing.)

I wouldn’t be surprised if with some improvements in design I could boil enough water for a reconstituted meal and put the kettle back on for tea or coffee to follow. I’ll have to work on new designs and start comparing performance. I reckon there’s going to be a critical balance between increased air input for hotter burning and insulating the stove – too much draft blows a fire out. I’m not sure what’s the best workable size of crushed fuel either: in other words, the finer it is the faster it can use up the air input, but the harder it is to have it supported on a grate, or avoid it getting blown about, rising as sparks. Powdered fuel can also fuse and choke the fire – I’ve seen it with coal on an open fire when you have a lot of coal dust left in the bottom of the scuttle and pour it on.

The coal burnt in coal-fired power stations is finely powdered, but it’s blown into a furnace like petrol injected into a car’s engine. A high-tech stove might well do something similar with powdered carbon products made from char. Of course, one way to go with this is to force air through it with a PC fan or something, but I’d like to keep it low tech – but clever low tech – and avoid the weight of the fan and batteries. I want my stove to be a simple hobo stove for burning twigs when that suits me – I love the smell for one thing – but at other times (like for stealth camping) I want a cleaner burn. I think I’ve found it.

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4 Responses to My Pocket Charcoal Chimney

  1. Chet Atkins says:

    Nice job! I’m gonna try this with charcoal.

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  3. Uncle Billy says:

    I know this is kind of late coming (I just discovered the posting), but it occurs to me that instead of carrying all of the charcoal, some of it could actually be made while sitting around a campfire. Just a thought.
    Great info on the stove though.

  4. lettersquash says:

    Thanks Uncle Billy, that’s a great idea. I haven’t made charcoal yet, but I might get round to it. It might be useful on a longish trip to make some before moving on, and then it would give quick, hot and almost smokeless fuel for the evening meal when arriving at another campsite. I hope to do some more backpacking with the charcoal stove (or a new one) later in the year.

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