Box Rocket adaptation: back to the drawing board...

Hi there,

This is the first stove I've ever had a crack at making; my version of a Pekka Leskala style box rocket, but I'm afraid I don't have the great man's gift for stovemaking yet!
Here's a video of it, warts and all.
I look forward to hearing where I went wrong

I'll keep working on this, and let you know how it goes.

All the best

Matt

 
Hi Matt, You definitely have the gift for metal work, but as you say its your version-your style.
Where you went wrong was you altered the working proven tested version.
so remove the warts and all. just make the larger, to scale version of pekka's ..and it will work fine.

I would say, Because you added the baffles, and because of air leeks, the draw is week ..the riser is not hot and will not pull on the fire box, its all cooling down before it reaches the riser.

Remove the added baffles and do another test burn: gr8 crack ..Best regards Bob.

I agree with 2nd burn. To reinforce his remarks, first of all, the stove has to be air tight. Your stove is not air tight and since the burn chamber is vertical, hot air smoke and gases moves to the closest exit, that is upwards. The air that is feeding the combustion is coming from the gaps you have in the stove. Also, your chimney is not high enough to create enough air draft. How I would solve the problem? First, get 2 metres os chimney and try to attach it to the stove to create more draw; second, make all the stove air tight and get a lid for the wood loading chamber so you can control air inflow; third, get a way of closing the secondary air if needed. once the stove gets to operating temperature, open the secondary air; fourth, if you have deficulties to start the fire and there is a lot of smoke coming out from the wood loading compartment, you will need to make a bypass to the chimney to start the fire. Once the stove is hot, you can close the bypass.

Hi 2nd burn and Caotropheus,

Thanks for taking the time to consider my first attempt, it is much appreciated. I will try and implement your suggested changes and come back with the results next week.

All the best, and thanks again,

Matt

It works!

Pekka wrote to me with some recommendations which I followed and it now works, and is heating my home as we speak! I'm delighted, and will post pics and videos soon.

sounds like your more than happy with your build

as youve found out it comes in handy to have help by recommendations by other members it also helps to improve your build or mistakes that we all make

inkmotor wrote:

It works!

Pekka wrote to me with some recommendations which I followed and it now works, and is heating my home as we speak! I'm delighted, and will post pics and videos soon.

I would like to see the pictures and video. Thanks.

Hello again all,

So here it is installed, and looking pretty toasty. It burns hot and clean, (not the slightest trace of smoke out the chimney) but it is hungry, and I have yet to learn how best to manage it in order to achieve a sustained cosy burn, and not devour so much fuel.

As a means of quickly heating a cold room it is stunningly effective; loaded with +/- Ø10mm hedge cuttings it goes from stone-cold to literally red-hot in around 90 seconds, but of course the first load of fuel is then almost completely spent in just a few minutes.
I believe I am seeing surface temperatures easily over the 500ºC mark, judging by the information here http://www.hearth.com/talk/wiki/stainless-steel-properties/

In order to calm the thing down I have played with choking off the primary air intake, albeit imperfectly (this 0.5mm stainless steel is terrific for prototyping but next to impossible to get air-tight, unless you are Pekka Leskala), and of course the more experienced of you will already know what happened: the narrower I made the primary air intake, the hotter the stove got as the velocity of the air coming in increased. It was paradoxical at first for me to see the stove cooling as I opened the primary air intake, and glowing more and more fiercely as I closed it.

The coolest burns happen when the primary air intake is fully open, but the problem I have with that is that, perhaps due to some unseen little air leak, I get flames creeping up the fuel, and very occasionally little puffs of smoke eventually start peeping out the top. Mainly though, any smoke which does happen to rise from the fire simply rolls over at the mouth of the primary air intake, and is pulled back into the stove. I am unable to perfectly achieve the true rocket burning pattern just at the tips of the fuel. That is in the main what happens, but eventually, the rest of the length of the sticks catches fire too, though thankfully the flames do point downwards into the stove due to the down draught.

Has anybody experimented with choking the secondary air intake on their stoves? What is the effect of this? Is it still possible to get clean but slower, sustained burns?

How can I get the fuel to just burn at the downward tips?

Perhaps if this model were constructed properly out of heavier steel and welded together, it would burn 100% rocket style, just at the tips of the wood.

I heated our whole little house (approximately 84m^2 or about 828 ft^2) for six hours on approximately 10kg of seasoned privet hedge cuttings (approx Ø 10 - 60mm x 250mm long) and 2kg of kauri, a native NZ hardwood. I will have to buy a thermometer to get a handle on the figures, but it was warm enough to pad around barefoot in t-shirts in the living room, (I think easily upwards of 25ºC) and the rest of the house was very comfortable too, so must have been 21ºC or over in rooms away from the stove, whilst outside is was hat and coat weather, around 10 - 12ºC.

I look forward to hearing your comments.

All the best, and thank you for the help and interest you have given me,

Matt

Stove installed! (and just beginning to glow slightly at the front):
https://www.dropbox.com/s/pevdy02d6fhr5l4/DSC_0121.jpg


Stove burning too fiercely: here it is just two or three minutes after being lit, loaded with Ø 10mm privet twigs. Don't worry, the shot is a little over exposed; it was nowhere near white hot at the front, but certainly a disconcerting orange. Naturally, I try to get it to burn cooler than this by adjusting the primary air intake (in this picture it is as closed as it can be, and thus as hot as it can be)


A steadier burn, glowing a dull red: Matt's box rocket in action

that fearsome burn photo didn't work, here's another attempt:

Stove burning too fiercely:

here it is just two or three minutes after being lit, loaded with Ø 10mm privet twigs. Don't worry, the shot is a little over exposed; it was nowhere near white hot at the front, but certainly a disconcerting orange. Naturally, I try to get it to burn cooler than this by adjusting the primary air intake (in this picture it is as closed as it can be, and thus as hot as it can be)

inkmotor wrote:

In order to calm the thing down I have played with choking off the primary air intake, albeit imperfectly (this 0.5mm stainless steel is terrific for prototyping but next to impossible to get air-tight, unless you are Pekka Leskala),

nice build but it try a different sealing method conside using the cooper roof folding method like this



ive used this techneque often and the old systems used to use this method handy on thin sheets and for sealing up by placing against a hard surface and pounding it with a hammer

Thanks for that Gadily, very neat system! I don't have those tools though, and generally used Pekka's hammer technique where I could:


For a more durable and stove, I think next time I would use heavier gauge steel and weld it together.
Having said that, the night before last we heated the house very satisfactorily, again for five hours, using a combination of privet hedge cuttings and old kauri demolition scrapwood, and my growing understanding of how to use the primary air intake. Having the lid half open or more, thus allowing a generous but slow flow of cool air in through the top seems to make for more prolonged, steady, but still smokeless burns.

this pipe i made was using the above method with just a hammer and a sharp edge of vice you dont need special tools

https://servimg.com/view/18708992/1

https://servimg.com/view/18708992/2

how i did that was with bending 1/2" up on one piece the other was an 1" stood up bending back on the 1" by 1/2" and folding flatish with other piece sloted into it then folding it flat against the metal surface this gives you a double seal with no welding