Rocket Stove not rocketing

[Screwdriver]

That makes sense, so you are still getting the heat that would normally escape up the flue. Your sketchup diagram looks spot on, I think I will try a garage version like that.

The rocket stove or rocket heater/burner is a fascinating and very clever piece of technology. The science behind it is equally fascinating which is how I got into them. Having said that, there are some fundamental design parameters you really need to get in the right ballpark; size of the firebox vs. size of flue and size of the primary air inlet. They need to be within a certain range of proportions. Remember you're building an air pump and air is heavier than you think at this altitude.

For example, take an average size room, say 6m x 4m, 3m high. Ok, that's a smallish room or a biggish shed. How heavy do you think the air is in that size space?

Wrong! If you gathered up all the air in your room, filled a balloon and weighed it, it would be over 70Kg!

IKR. Hard to believe but one cubic metre of air weighs 1.2Kg. Great little anecdote for the kids or free rounds down the pub...

But that weight or pressure can work to your advantage in two ways. Firstly hot air is a lot less dense and therefore lighter so you don't need that much of it in your insulated flue to start shoving cold dense air out of the way. Secondly, once you start shoving it, it develops a momentum in whatever direction you coerce it, especially if that volume of air is contained in a flue. Hence the need to get your volumes and apertures the right sort of size and relative proportion.

 

[delta9]

Yeah I thought it would be an easy project But i'm not very technical at this sort of stuff.

Thanks again for all the info and help. I've only managed to sort the gap between riser and baffle plate, I did not have thick plate so opted for 50mm firebrick to take the brunt... And put original gas bottle head back on.
The gap is now 40mm instead of 200mm.

Not much improvement there to report, Still not rocketing and big tank is no way getting hot enough... And still smoking from chimney! Got to be air or (and) insulation?

Will keep trying and do what gaz suggests with the air intake pipes

 

[Screwdriver]

Try posting some better pictures. I can't see anything from the supplied pics. Diemsnsions would be handy too. Might be something simple. It's not rocket science, you just need to be in the right ballpark then tweak away.

 

[delta9]

Thanks will get some info/pics posted tomorrow

Cheers :-)

 

[delta9]

Well I've added a 'jacket' over air input pipes, hot air is now being drawn from underneath, but unfortunatly still no rocket action!

I've not added primary air control yet, so would too much draw prevent rocket action?

I know its currently drawing very fast as its going through alot of wood, I did slow it down a bit (by putting some steel over intake), that helped on consumption but did nothing for the rocket action.

Wondering if I have my secondary input the wrong way as mentioned? Also should I also be pre-heating the secondary air?

I should also mention the riser is stainless steel 125mm, but 3mm wall (not 5mm as mentioned earlier).

Cheers for any help!

 

[bigegg]

drawing fast and going through a lot of wood?
sounds like it's rocketing to me?

 

[delta9]

But im still getting alot of smoke out chimney (which I guess is unburnt fuel).

and heat exchanger not getting that hot. I cant hold my hand on the exchanger but compared to the firebox which is 10x hotter, if that gives you an idea.

I would have thought the heat exchanger would be hotter than the firebox?

 

[bigegg]

But im still getting alot of smoke out chimney (which I guess is unburnt fuel).

and heat exchanger not getting that hot. I cant hold my hand on the exchanger but compared to the firebox which is 10x hotter, if that gives you an idea.

I would have thought the heat exchanger would be hotter than the firebox?

the firebox should be so well nsulated, you can't feel any heat from it.

if you can, it needs more insulation.
the *only* way heat should escape from the firebox is via the heat riser.

 

[Screwdriver]

Damned if I can work out how that is set up. Doesn't look like a rocket stove to me. Critical issue is the firebox and flue need to be heavily insulated. If I am reading the pictures properly (at all) the firebox looks far too big.

 

[maz0]

As has been said above, I don't think you have been considerate enough of dimensions. Kinda looks like a firebox plonked on the front to make the rough shape of a J, but it really needs to be tighter to get that air flow.

 

[gaz1]

delta you didnt do what id suggested by shortening your firebox to your cylinder

you should have something like this



no matter where you put that flick the secondary air should follow the secondary firebox straight side as this preheats your secondary air

the reason why you could be having issues is the smallness of your secondary firebox in red 4" isnt a good flow of fire

the light blue (turquoise ) is your primary air into the system super heated from your secondary firebox over the top of the main firebox down then enters the firebox at the front

these need to be around 3/4"-1" round drilled holes x 4 to 5 of them

that firebox wants a trickle of air under the ashes as this also allows you to start the fire much quicker but gives extra air input

the light blue under the system is primary air controled at the front by push/pull air controllers through to the front on a cool bar

the dark blue is your secondary air input taken from your primary air not controlled but if you want to test this close the secondary air off by shoving something in the end

if you are close at the top then the top should really get hot when it throttles up and it will unless something is wrongly built

not close enough at the top
not enough air going through the system

if you are chewing through wood then your secondary air isnt allowing enough air into the system this should take over from your primary air and really fire up your system in the vortex tube / riser tube

firebox too far away from the riser tube can cause problems your seeing as not able to truly burn corectly

my opinion block off secondary air and try a burn in it that top should become red hot and glow at full throttle leave your door open to try that while firing it

when you shut the door the heated primary air should take over with enough air to create a good burn

be warned your secondary firebox will glow pure red burning the above way as mine does

 

[gaz1]

query here but what is this marked in red if thats the pipe there it shouldnt be there

as its only meant to stop at the side wall ( marked in purple )otherwise your firing the secondary air at the far wall effectively stopping the spiral the first pic was to show you where the tube belongs not all the way through it to other side as you was lost on where to situate the secondary air

other query is

whats the looks like a pipe coming up through the floor of the secondary burn box

neither should be there

 

[Screwdriver]

@delta9 I think I have a handle on what you are doing, it's not a rocket stove. Looks like you made a regular wood burner and a separate (insulated?) flue. By the time the flame reaches the flue in that design, the flue temperature will be too low to allow full combustion; most of your precious wood gas will end up being pumped out of the flue unburned.

The "trick" to the rocket stove is not just the rocket angle promoting a "turbocharged" draw, the firebox and flue must act as one component, effectively lengthening and concentrating the burning fuel. The flame front extends all the way from the firebox to the flue, then "just in case" you can add a bit of secondary air to the end of the flue to allow the last of the wood gas to combust. For that to work, even the end of the flue needs to be at very high temperature.

Sorry dude. That design looks flawed. Best bet is to start again and make it more like the diagram maz0 posts above.

 

[gaz1]

your secondary air pipe is wrong youve gone fully through it



in small red is your secondary air pipe

where it is thick red it should be cut off at wall side where ive drawn it

 

[gaz1]

@delta9 I think I have a handle on what you are doing, it's not a rocket stove. Looks like you made a regular wood burner and a separate (insulated?) flue. By the time the flame reaches the flue in that design, the flue temperature will be too low to allow full combustion; most of your precious wood gas will end up being pumped out of the flue unburned.

The "trick" to the rocket stove is not just the rocket angle promoting a "turbocharged" draw, the firebox and flue must act as one component, effectively lengthening and concentrating the burning fuel. The flame front extends all the way from the firebox to the flue, then "just in case" you can add a bit of secondary air to the end of the flue to allow the last of the wood gas to combust. For that to work, even the end of the flue needs to be at very high temperature.

Sorry dude. That design looks flawed. Best bet is to start again and make it more like the diagram maz0 posts above.

the second part your spot on screwdriver the first part your wrong

its a super heated primary air rocket stove the primary air heat is so hot the wood starts to give off its gases

maz0 and your design is old school based on permes old design of rocket stove use by watching and loading most of the time slow down by blocking off the air at the input basis

the new design is based on a closed off firebox hardly any chance of spit backs or creating a chimney in the firebox coming back into the room

the secondary air wasnt used at permes until there star started to implement it via his batchbox design then permes jumped onto the bandwagon but still want many to build there way of old design

seconday air allows you to burn even less wood but fires up just the same heat output as if you was firing at full throttle

 

[gaz1]

both of these systems use preheated primary air

if he gets that right he will be close to this output preheated primary air

a purple flame coming off of it its that hot

peter van designs leaking like a sieve look how much air input it uses no preheated air

this one has a door fitted but also leaks like a sieve

maz you will like this so take a look

 

[gaz1]

what ive seen now your going to have to cut it all open sorry about this now i understand it didnt help when you created a quick build

first off cut the plates back off that youve just welded no choice on it

then cut where ive drawn on the tank picture below



this is so you can get all your pipe out or cut it close to the firebox say 3" towards the vortex pipe this allows your firebox to be seperated from the secondary burn box

then cut as above picture where you have welded to get your secondary burn box and vortex pipe out again if you cut the bottom away you should be able to get at the secondary air pipe and cut it against the wall

now pretest it by putting some wood in it and lighting it it should give a good flow of fire up the tube in a spiral

you need to create something like this run it down its secondary firebox and in just before the black center line the purple line is the vortex tube upright

you can either run the secondary air through the side or run it to the floor below the system to collect air from below this needs to be about 1" square tube or 1 1/4" round tube 1" tube is smaller air input than 1" box section



once that is tested and the flame runs up the inside of the tube if you have it right and it will if you have that secondary air in its right place

its the best way to test the tube and vortex pipe

this video shows this actual effect as i moved that box section in to find its sweet spot as the flame came right out of a 1 meter high vortex tube or if you want to call it riser tube

test 14

page 3 and 2 show all my tests before i built one in all different configurations the main one was built in stainless steel tube 4" 2mm thick and a 4 3/4" 3mm box section

test 11 shows it in place but not at its sweet spot like on test 14 on the below links

https://www.dailymotion.com/user/gadily/2

once tested and it does like my flame did then you can fix up the box to the gas bottle but you need a space of 3" at side of gas bottle so that means your secondary burn box wants cutting smaller also means your firebox box section wants cutting off as well to reweld the secondary burn box to the firebox

but build it in stages come back at each test fire does it work show pics not jump in with both feet many make that mistake

 

[Screwdriver]

the second part your spot on screwdriver the first part your wrong

LOL. Yeah ok, whatever you say dude.

@maz0: crack on mate, you're in safe hands, that thing will burst into flames any minute now, just keep watching all those videos, ignore the science waffle and it will just magically start working.

 

[selectedgrub]

 

[maz0]

LOL. Yeah ok, whatever you say dude.

@maz0: crack on mate, you're in safe hands, that thing will burst into flames any minute now, just keep watching all those videos, ignore the science waffle and it will just magically start working.

Whats bursting into flames? I’m not even building anything ... you have me worried now

Guessing you meant OP? delta9

FWIW I’ll be following this book when I build mine, the authors have built several hundred of them and all the variations with drawings and science to back it up so hopefully in good hands!