Pyrolysis kinda type stove

[Gailainne]

I found this link recently, to a wood burning stove with a difference, so I thought I would try it. (trying to find it again, will link it promise)

Impressed I'll say, 30 mins burn on a handful of pencil sized branches, would'nt you be ?

I used a catfood tin, I guess anything similar in size will do. I wrapped a peice of paper around the can to get a farily accurate circumference, and used it to lay out the various cuts as shown on the site.

I also used a coat hanger for the bits and bobs, and some kitchen foil for the windshield.

Anyway the results;

The components

Fitted together

Packed with small wood

Fire started 0 mins (used paraffin as indicated in the plans, not much is needed tho)

Windshield added

At 5 mins

At 10 mins, (windshield sorted )

At 15 mins, here you can clearly see the secondary slots supplying air

At 20 mins, notice how little smoke there is

At 25 mins, flames gone, but charcoal still providing a lot of heat

At 30 mins, heat still more than enough to keep a simmer going

It burns from the top down. which is surprisingly hard to get your head around, but damn can you dispute the results, give it a go, you will be impressed, trust me.

Stephen

 

[scoops_uk]

Top stuff - thought of any enhancements for a MkII version?

Scoops

 

[Gailainne]

Scoops

I'm gonna get around to a firebox at some point, wanderingstar, let me see the one he got from a fan in the states, which I've CADed a few variations on, but at the moment this is intriquing me. It uses so little fuel its amazing. A combination of both might be viable, again something I'll play with on CAD before trying it for real. Fascinating stuff I'm sure you will agree.

Stephen

 

[scoops_uk]

The pyrolysis thing really does seem to push a small amount of fuel a long way and it really cuts down on the smoke too.

I had a go at trying to burn woodgas by messing around with the air hole placement on my stove but never quite got it working well. I think the concentric cyclinder approach is probably the best way to go with a small stove. Otherwise iIt's too hard to control the secondary airflow in such a small volume chamber so that the wood gas burns well.

Scoops

 

[gorilla]

that is very impressive - i looked up pyrolysis on wiki, but my head fused before i got halfway down, so this pyrolysis will be to me like a telephone - i'll use it, i know it works, but i don't know how or why it works

 

[born2roam]

Great stove indeed.

Tried it some ime ago and works wonders. I have one can which holds a waterbottle on my "bumbag" on one hip, another bottle with a similar can, which acts as a billie on the other hip and Bob is your proverbial family member...

Advantage that it now takes up a lot less space and it's shape is protected. Personally I have always dented (etc.) round wood fire stoves. Which is why I started playing around with similar ideas to Scoop (too flash for my two left hands to create, but a splendid piece of work!!) and the Nimble Will Nomad (actually I have one fire box somewhere)...

First time I found the gassifier (spelling?) stove was a couple of years ago on

http://www.garlington.biz/Ray/WoodGasStove/index.htm

or

http://www.imrisk.com/woodgas/ddstove.htm

Grtz Johan

 

[Gailainne]

Nice links, it was the Garlington stove I based mine on.

its intersting how low the stove shield is on the second site, its lower than the secondary air slits, I'm not sure thats right, from what I have read the annulus allows the secondary slots to draw preheated air thru giving a more efficient burn.

Anyway I have to find some thicker aluminium foil (search in morrisons should yield something) the kitchen foil is just to flimsy to use as the stove shield, I was continuously fiddling with it, something thicker will allow a stiffer cleaner shape, and thereby flow, it should also let me make and position the air slots more precisely.

A project and making fire this weekend,

Stephen

 

[Glen]

I had a go at trying to burn woodgas by messing around with the air hole placement on my stove but never quite got it working well. I think the concentric cyclinder approach is probably the best way to go with a small stove. Otherwise iIt's too hard to control the secondary airflow in such a small volume chamber so that the wood gas burns well.

Scoops

Hmmm, how about cutting upper slots then using a sliding sawtoothed damper ( or on a cylindrical stove a rotating one ) Carefull spacing of the slots and sawtooths should give everything from fully open to fully closed. Probably easier to design one that's finger ajustable hot for a flat sided stove. Initially I'm thinking a metal ruler running through some fixings on front & back and just push/pull it/them

 

[Gailainne]

Update to this,

I tried various ways of creating this stove, but in the end I just could'nt get it to put out enough heat, for long enough to even boil a cup of water, so I had a rethink.

This is what the mark 2 looks like

Its made from a standard cat food tin, and a slightly larger tin which held new potatoes.

The secondary air supply holes

The bottom holes which feed both primary and secondary holes

Internal, should just see 3 of the 6 primary holes

The bottom

However I could'nt get this to bring a cup of water to the boil either , small bubbles yes, but no more.

Time for drastic measures, I had a rake in my bits and pieces boxes and came up with quite a few computer fans, all run on 12v but, a 9v battery runs them just fine

Boy oh boy what a difference

The set up, I used a 4" fan on this test

After 4 minutes (I used 4mm compressed wood pellets, but only 2 handfuls) basically cat litter

Amazing shot of the secondary holes, the flames actually met in the middle and spiralled, looked very cool

Brought 1 litre of water to the boil in just under 9 minutes

After that I switched the fan off, it carried on boiling the water to the 17 min mark then the flames died away, charcoal still provided a lot of heat.

Without the fan I had to use paraffin to get consistent lighting, however with the fan I only used some wax soaked cotton wool, small pieces were more than enough.

BTW dont leave the fan under the stove after you switch it off

Thermoplastic and heat, result, horrible smell, melted duct, surprisingly the fan still works

So I had a very lightweight stove which burned wood very efficiently, but required an electrically powered fan to accomplish it not a bad thing, I just would have liked options, so another rethink.

Tonight I came up with the answer;
the problem I have always had, is that the fuel burns out before bringing the water to the boil, I didnt want to increase the size of the container, so I had to increase the amount of wood in the container, (4mm compressed wood pellets dont work, been there tried it, needs the fan), solution, pack the wood in vertically, it need to be of a length that sits just at the secondary air holes, and different sizes so there are gaps for the air to travel upwards
Like this

Unfortunately its back to using paraffin to start it, but I'll work on that.

At 5 minutes it had brought 0.5 litre of water to the boil

Here you can see it in full swing (BTW this is the original can with the 4 holes bottom and 4 slots top)

It lasted a total of 15 mins, with enough heat to still keep a simmer going.

NB I'm still not sure why the bigger pieces of wood I originally used didnt work, I'm wondering if the sticks with their greater surface area produced more heat ?, dont know, just a guess.

I'm quite chuffed, I now have a system that I know will work whether I use the fan or not.

Next thing to work on is a speed control for the fan, a Maplins I shall go.......

To be cont

Stephen

 

[scoops_uk]

Don't forget a solar panel whilst you're at maplins then you can operate without the battery.



Scoops

 

[Gailainne]

Already got one, but its for my mobile phone and GPS it wil also recharge AA's for my torches, so a nice bit of kit. Ask the guys on the Vildmark course, they saw all my techno bits laid out on my poncho

 

[scoops_uk]

Is it a solar panel with a built in battery? They're rather handy If not try 4 NiMH batteries in one of those plastic battery holders, they put out just the right amount of current to charge all sorts things (NiMH are definitely best for this) and are easy to top up with a small panel.

Have you tried making a taller version of the stove? It might generate enough airflow without the fan?

Maybe try adding a tin with lots of big air holes round the base below your current model as a stand and see what effect that has? Stability will suffer, but if a bit of extra height makes a big difference....

Scoops

 

[Aragorn]

is this the sort of thing you have scoops, looks quite good if a bit expensive, but overtime should make a saving on the batteries, stove looks very interesting, am wondering now if i could convert the hobo stove i have by adding an exterier container

 

[scoops_uk]

It's one of these although I paid a lot less for it on ebay

Scoops

 

[Gailainne]

There is a design on file that uses 2 same sized cans one on top of the other with a gap between them, bottom one is the combustion chamber, the gap is the secondary air supply, top can is open top and bottom, however as you say it would be very unstable without some kind of supporting frame. Something to play with, but not sure how suitable, or packable it would be for camping tho, perhaps some kind of nesting system, shrug.

Stephen

 

[Gailainne]

Its a freeloader I have, comes with a sh*t load of adaptors for all sorts of phones, ipods and whatnot. I've been looking at another one, folds in half and carrys/charges 10 aa batterys, 12v system, the links at work.

Aragorn why adapt your hobo, this is just some empty steel food tins, admittedly I especially bought the new potatoes for the tin, but they got ate

 

[Scots_Charles_River]

Good post. Interesting stuff. I have a spot welder in my school so need to buy some tins and start welding !

Ideal would be a combo of yours/pyrolsis and Waylands tin stove/hobo stove. The fan is a problem I think.

Nick

 

[Glen]

The fan is a problem I think.

Nick

That's why I opted for a side mount for the fan in my Hoblow stove, it helps with stability too.

http://www.bushcraftuk.com/forum/showthread.php?t=17516

 

[Scots_Charles_River]

Aha, good idea.

Nick

 

[Glen]

However I could'nt get this to bring a cup of water to the boil either , small bubbles yes, but no more.

The set up, I used a 4" fan on this test

After 4 minutes (I used 4mm compressed wood pellets, but only 2 handfuls) basically cat litter

So I had a very lightweight stove which burned wood very efficiently, but required an electrically powered fan to accomplish it not a bad thing, I just would have liked options, so another rethink.

Tonight I came up with the answer;
the problem I have always had, is that the fuel burns out before bringing the water to the boil, I didnt want to increase the size of the container, so I had to increase the amount of wood in the container, (4mm compressed wood pellets dont work, been there tried it, needs the fan), solution, pack the wood in vertically, it need to be of a length that sits just at the secondary air holes, and different sizes so there are gaps for the air to travel upwards
Like this

I'm quite chuffed, I now have a system that I know will work whether I use the fan or not.

Next thing to work on is a speed control for the fan, a Maplins I shall go.......

To be cont

Stephen

One thing that I realised during my experiments with a Clikstand as a firebox ( I really need to do potos but the basic idea is here
http://www.bushcraftuk.com/forum/showthread.php?t=22041 ) was that we have been getting the windshield all wrong with most of these stoves.


Low down it doesn't need it, the can does the job, infact I think a windshield in this position actually slows the airflow.

Where it would create 2 benefits is up at the level between the top of the burner box and most of the way up the pot. Positioned there it would both shield the pot from heat robbing wind but also if designed right would add to the chimney effect.