Above shows the overall layout. bellow you can see the small shelf I made to create a venturi vacuum to draw in the secondary air
these pictures show the shape of the port
sealed up with clay
all wraped up in ceramic wool with a fire in
and here are some pics of the double vortex, first one is right at the beggining of the burn, the second image shows it once it has got going a bit
Though there are a lot of details that need to be tuned with this design, one thing was clear, it is very resistant to stalling with a restrictive heat exchanger. holding the steel plate about 1cm above the riser had no noticable effect on the combustion, it only started to struggle when I squeezed it down to about 5mm. other things i like about this design are that the angled floor of the fire box make it self feeding, though the fuel load is quite small. One of the problems was that it did start to burn the wrong way out of the fire box, though not very much and only towards the end of the burn. if you look at the first picture that shows the basic layout, it did supprizingly well. next I'll reduce the firebox opening by changing the shape and location of the secondary air feed tunnel, get some barrels for the stove at the weekend, and get myself a flue gas analiser
should I put my secondary air in at the top or bottom of the port?
I think the design goal is to have a small responsive fire that burns well at a range of different temperatures. After I have stoked the thing to the max for 20 mins to bring 70L of food to boil, and I want to simmer it for an hour. when I put the minimum amounts of wood on the embers, I think Ill want to close the primary air down and leave the secondary air open. My instinct is that the bottom fed secondary air version would burn cleaner than the top fed when its closed down like that.
Here is my pan in a barrel. I dont think I'm going to fit a pot skirt in their! Oh well. Bellow is the internal shape and the external shape of my mold, made from all sorts of rubbish. I think I will put my internal mold shape in a black plastic bag then suck the air out with my hover, to keep the moisture off the card board. Right at the bottom are some details of my internal mold shape. I spent a good long time on the details of that shape. I'm going to the scrap yard tomorrow morning to see if they have a good long chimney pipe that is 80 to 100mm diameter, like a lamp post, or maybe an old iron drain pipe with a 90 elbow. That riser is almost 80mm (its not long enough yet, I know). I hope I'm right in assuming that my chimney should be the same diameter, or a little larger than my riser, which is 3.5", so I'm going for 3.5-4".
Oh, my plan is to cast it all in the barrel, with support rods in place. the cardboard tube that is going to define the feed pipe has a hole cut for it in the side of the barrel, and there will be a variety of rods and bits of metal that will connect the refractory shape to the barrel in place. the whole thing will be on a board on bits of wood, then I will hit that board with my hammer drill to help vibrate things into place a bit, though I am also going to fill and assemble the mold in layers, so the vibration is for detail, not for moving large amounts of material round corners. I'f I'm really lucky, this level of effort will be just adequate. If not, I got a whole bunch of people who are expecting a wood fired cooker to disapoint on satarday. feeling the pressure.
If anyone could comment on my chimney issue, same as riser? or 5" like a standard instove. I think same as riser, or somewhere inbetween. Help
The cast refractory came out a treat, all my chimney parts are cut and prepped for welding, I got all my ingredience, but its dark, getting later, and im waiting on a guy from ebay to deliver my new welder, so either my welder wont turn up in time, or my refractory will explode when i'm cooking tomorrow, or it will all work out great. this is all very exciting for me. is anyone reading this?
the refractory is quite soft and damp feeling still. I hope its going to be ok when I fire it up tomorrow morning. I think Ill give it some gentle burns tonight to hurry it up a bit. How long should it take?
a replacement o2 sensor costs £50. might have to get one of those soon.
Post by esbjornaneer on Nov 29, 2015 6:57:53 GMT -8
For sure there are people reading it, a shame you did not get any answers from the heavy weight contributors at the end... It will be great to hear how it all worked out in the end. I take it that it worked OK after the first hour.
great timing because as you sent that message, the stove was on its second voyage feeding the troops of the london climate march.
so, the first firing (last month) was a gradual transition from working terribly to working acceptably by the end of the day. as I said, i think it was about the refractory concrete curing process requiring heat to purge the moisture, which sapped energy from the fire. after the first firing there was a really clear line on the refractory about half way down the fire box that marked the transition from the material that had been purged of residual moisture to material that had not. to prep for last nights event, i put the combustion chamber on the barbecue and built a fire beneath it and in it at the same time. this worked perfectly.
Yesterday the fire worked spectacularly well. I have no idea whether or not it would produce a stellar emissions graph (though I would love to get a flue gas analyzer on it) but attaining smoke free combustion was very quick on start up (maybe 30 seconds, using a petroleum firelighter and a handful of twigs), smoke free combustion was very reliable even using damp twigs collected in the park, all this is very important when wheeling the thing around in a dense crowd of people (oh the liabilities, boiling hot food, fire, and a huge weight of metal on wheels, not to mention food hygiene!). The temperature control I wanted is there too, i could occasionally add a couple of larger twigs (less surface area for more fuel) and maintain a simmering temperature, or bring the 50L+ of soup up to a vigorous (but not excessively so) boil by stuffing the combustion chamber full of small twigs, and though keeping it burning hot requires very regular refueling, when neglected it will hold a bed of embers from which it will quickly relight for ages, like maybe over an hour. I started the soup by bringing 5L of veg oil up to temp and deep fat frying pearl barley, potatoes and lentils. so, 80mm diameter riser seems like a very good size combustion chamber for my 77L pot.
Overall, I'm rely pleased with the functionality of the thing, though I would really like to get an analyzer so that i can hone the geometry to get it working at its very best. also, because the diameter of my pot is only about 5cm less than the diameter of the barrel, i don't have enough room to fit a pot skirt between the pot and barrel, so I have not really been able to test the resistance to stalling by a restrictive heat exchanger cavity, which was one of the main design goals. I might test it actually, ill end up with pretty much a 1cm gap all round, but i doubt this will be enough.
One other thing that i think will be of interest to other builders is how simple my mold making technique was, which worked fine. you just need to make your shape out of cardboard and duct tape dense enough to resist compression, and if i were to do it again i would try and make the blocks of card board that fill it to be a bit smaller, as this would make it easier to pull them out, but if time and money are limited and you just want to get a novel shape made up in a hurry, then I would say don't let the need for perfection stop you. that mess of whiskey tubes, cardboard, duck tape, glue and silicone pictured above worked out great for me.
That's the best picture I have of my setup yesterday. I'll upload some details of the combustion chamber when i get home.
of the topic of rocket stoves, that trailer i made totally failed. I pushed it for ages with 2 flat tires before one of the wheels completely collapsed half way between Trafalgar square and the houses of parliament (within sight of the finish line!). So that is the kind of thing that might happen if you are as cheap and slap dash as me. still, we fed a huge number of people and had an excellent time.
martinm: any one here with info \ experience with heat (from a mass heater) distribution with ducts throughout two storey house ?
Sept 8, 2018 22:58:52 GMT -8
padica: Good morning, this is a wonderful subject, please someone can help me with the theme of double and triple combustion, how it is achieved, theory and design, thank you
Sept 15, 2018 7:13:40 GMT -8
wiscojames: I'm afraid you won't get a response to such a vague question - I suggest reading through some of the threads related to your questions before asking for an explanation. People will be very generous with their knowledge if your question is more specific.
Sept 18, 2018 4:48:00 GMT -8
daniel: in my experience as I am working now on something of that nature, I have thought of making a heat exchanger and distributing the heat through vents using a slower fan. Now after a few years I realize that mass heaters give out primarily radiant heat, for
Nov 30, 2018 12:48:38 GMT -8
coastalrocketeer: Anyone posting in this shout box... if you have something you want people to see and respond to, create a thread in the appropriate forum section... this is not the place...
Dec 16, 2018 18:10:49 GMT -8
vesuvius: High Temperature Glass options,
Jan 4, 2019 16:28:17 GMT -8
vesuvius: Do any of you have experience with using the glass from home oven doors on a rocket stove? I'd like to have a viewing port on my stove but don't want to fork out for new ceramic glass. Any thought as to whether it would take the heat of a rocket stove?
Jan 4, 2019 16:30:40 GMT -8
yaya: you dont need the blowair for that temp..
Jan 13, 2019 16:43:57 GMT -8
flybywire: Glass window from an old washing machine is designed to take high temps. Cheap solution to your need.
Jan 27, 2019 0:10:58 GMT -8
coastalrocketeer: Anyone posting in this shout box... if you have something you want people to see and respond to, create a thread in the appropriate forum section... this is not the place to have a discussion... it is for short announcements
Feb 7, 2019 0:11:23 GMT -8
coastalrocketeer: you won’t likely get replies to questions here, and it is not a spot that makes holding an ongoing discussion possible...
Feb 7, 2019 0:12:22 GMT -8
TexasGonzo: Sooooo glad I found this site! Its always rewarding to find such a super group of folks! To any and all, feel free to PM me anytime. Thanks for having me!
Mar 11, 2019 18:56:41 GMT -8
jlmtech: GADGET: CONSIDER USING A JET PUMP INSTEAD OF A BLOWER FAN TO INDUCE DRAFT; NO CLOGGING.
Mar 26, 2019 8:19:28 GMT -8
michaelegan: i am unable to open the sketchup files on my mac. I used sketchup a few years back but apparently the company now requires a subscription. does anyone have any advice/instructions on how to use the program or how to view pictures without spending money?
Aug 20, 2019 18:41:48 GMT -8
mannytheseacow: michaelegan: download AutoCAD student version for free... import .SKP
Aug 23, 2019 13:33:44 GMT -8
topbaza: hi everyone, been searching all over net and this is were i need to be i think!!
Sept 28, 2019 6:16:25 GMT -8
anounaki: Hi, why I cant upload photos when I make new tread to this forum?
Feb 28, 2020 2:09:40 GMT -8
ahansen: photos under 1 mb not possible?
Jun 4, 2020 0:09:21 GMT -8