The CANNON

[pxtyson]

I have been wanting to make a rocket stove for awhile
I wanted to make it for free and I dont make anything half ass.

I found some good steel around the shop and had to bore out the 90 but I think with the mass of steel will radiat heat well.

I hope the burn chamer is big enough but time will tell.

it weighs in at 16lbs.

[Donkey]

Sweet piece, looks bombshell sturdy.
The heat riser seems --- a little over-long.
I bet it drafts like mad!

What do you plan to insulate with and what will you be heating with it?

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By the way, the images you posted are a bit big. Could you please scale them down some?
640 pixels along the long edge should do it.

[pxtyson]

I left the riser long because it is easier to remove than add.

I have nothing to heat with it I just love fire.

I was thinking of placing it in a bucket full of sand.

[hpmer]

Sand is likely to not be insulative enough (too heavy). If you're going for free, you might try a bucket of ashes which will work fine until they settle and need to be fluffed up a bit. Otherwise, vermiculite or perlite work well.

[pxtyson]

I was actually hoping that the mass of steel itself would do the trick.

If not vermiculite is easy to find

I can't wait to see this thing burn, do you think the exhaust tube will work at that lentgh?

[hpmer]

The key to a really efficient burn is an insulated burn tunnel and heat riser, so burying what you have inside an insulative mix is what you want. The use of the heat produced comes down stream, either at the top of the exhaust tube for cooking applications, or by attaching the exhaust tube to a heat storage unit of some sort (this is where your sand idea would be useful).

You don't want to use the heat until all the smoke has a chance to combust, and that happens in the heat riser/exhaust tube, otherwise you are losing too much of it to the surroundings that should be going to smoke combustion.

The exhaust tube will work great, but is probably overkill. The usual suggested ratio is 2:1, so two inches of heat riser/exhaust for every 1 inch of horizontal burn tunnel. Your's seem a bit more than that ; )

[pxtyson]

I was hoping that with the long exhaust tube and the thickness of it that it would give off lots of heat once it is hot.

I will look into the vermiculite insulation once I know this thing works well.

[hpmer]

It will work fine and will throw lots of heat, but will be less efficient because of the lack of insulation (you're giving up heat to the room that should be combusting the smoke and gases in the combustion chamber). Given its thickness you may have more difficulty in starting it up since there is more mass to heat initially. Once that mass is heated it will pick up in "rocketness."

The length of your heat riser should compensate for some of this issue, but who knows how much.

My current stove is made from food grade metal cans and it works great. Very little mass to heat up and is surrounded by 4" of vermiculite insutation. The downside is that, given the thinness of the cans, they don't last very long, so I'm going to move on to a non-metal alternative.

[pxtyson]

I am still trying to understand all the principles of the rocket stove.

I am going to try to get this CANNON red hot tonight and see how it works.

I guess the main use for this would be as a radiant heater while we are camping.

[Donkey]

...
It should get to red hot, no problem.

By the by, I that 2 to 1 ratio is the minimum. I like it more like 2 1/2 to 3 to 1 instead.
In any case, it's all thumbnail. Whatever works, works..

pxtyson,
You will find that a raw rocket pipe will shoot most of it's heat straight up which is not nearly as useful for heating as it could be. You might find bell stoves interesting.. I can see your heater core inside an all-steel bell for space heating. It could be made pretty lightweight for portability.
You might want to try a down-feeding firebox too.

[pxtyson]

I guess the main reason for building this is to play with fire.

I am worried about trying this tonight because I live in a townhouse with many backyards looking into mine.

What are people going to think when they see me filling it with stuff and lighting it.

It looks like a cannon or mortor, well I guess I will find out tonight.

[hpmer]

Make sure you elevate it enough to see into it. The fire is fun to watch. Also, probably best to put it up on a brick or something non-combustible as it WILL get hot enough to burn stuff that's close, especially if it's not encapsulated in insulation.

[Teach]

Pxtyson, one thing I found with the last one I built "scaled down rocket" was that the feed tube because of its small size filled up with coals and ash very quickly. My observations were that if I had a larger area underneath the combustion area for coals and ash to drop through a small grate......the burn could be continued for a much longer time before having to be dumped/cleaned out.

When I look at your effort here, you have a similar trait in your design. I think if you were to flip the coupling section that receives the feed tube and heat riser upside down and plug the end that now is machined out to receive the heat riser. Then machine that same relief to accept the heat riser in the opposite end. That way you could have a larger area for coals and ash to accumulate. Without that area, you will find ash and coals accumulate very quickly and it's not long before it starts to impede the function of the stove by cutting off the flow of air.

[pxtyson]

Feb 24, 2010 7:37:38 GMT -8 Teach said:

Pxtyson, one thing I found with the last one I built "scaled down rocket" was that the feed tube because of its small size filled up with coals and ash very quickly. My observations were that if I had a larger area underneath the combustion area for coals and ash to drop through a small grate......the burn could be continued for a much longer time before having to be dumped/cleaned out.

When I look at your effort here, you have a similar trait in your design. I think if you were to flip the coupling section that receives the feed tube and heat riser upside down and plug the end that now is machined out to receive the heat riser. Then machine that same relief to accept the heat riser in the opposite end. That way you could have a larger area for coals and ash to accumulate. Without that area, you will find ash and coals accumulate very quickly and it's not long before it starts to impede the function of the stove by cutting off the flow of air.

That is exactly what happened last night.
I think what I will do is bore a hole in the bottom and add another steel dish that will hold these ashes. Have it so it will remove to empty.

[Teach]

If you can, ad a grate of some sort also so the coals stay off of the ashes and remain in contact with the wood you are feeding the fire with. Good luck and have fun with it!