Larger Firebox for the Rocket Bell

[joe]

Hey all,
I've been trying to come up with a design for the rocket bell heater to make it more user friendly...mainly in the form of a larger firebox. I attended a stove building workshop where we built a rocket bell, and despite its good performance, we were unable to come up with any reasonable solution to allow more wood to be loaded at a time. The stove we built can be viewed here: mha-net.org/docs/v8n2/wildac09f.htm. The loading method is the regular vertical feed tube.

My idea for a modified rocket bell is as follows:

Firebox is front-loading and sealed at the top

This is a single bell heater, with the chimney connection at the back

The baffle separates the upper part of the firebox into two volumes.
There is a slot above the baffle that allows some smoke to pass above it. The fire will be started at the back of the firebox, then the rest of the firebox loaded with wood. Airflow through the lower part of the firebox will then be obstructed by the wood, and some air will pass over the baffle to reach the firebox exit. This will hopefully contribute to good mixing of gases since the flames will be forced to go down by incoming air.

Once the fire burns down a bit, airflow will start to take a more direct route under the baffle, which is okay, because by then the fire will have creeped closer to the door, and we'd like to push those flames sideways through the hottest part of the fire rather than letting them go over the baffle.


Here we have the entrance to the heat riser at the back of the firebox. Note that there is a small slot above the entrance that could be adjusted to reach optimal performance. Since the the firebox exit is lower than the loading door, I added this slot as a safety feature to help keep smoke out of the living area if there was ever any trouble getting a draft established.


This shows the path the smoke takes from the heat riser, down through the bell and out the chimney.

Unfortunately I haven't the space to try to build something like this right now, but I hopefully I will be able to soon enough. I just thought I'd share the idea and see what everyone thought about it. I look forward to any comments or suggestions.
Cheers!

[gorbull]

Beautiful! But a real monster to build. Sure hope it works!

[Donkey]

Have you looked at peterbergs rocket bell stove?
He's having good results with a larger feed box, glass fronted for fire visibility, high efficiencies, the works.

I'm not completely sure that I understand your design...
Looks like the firebox top is above the opening to the heat riser. Even though you've got a slit for smoke to escape, I'd say the top of the box is likely to always be smoky..

Ermmm.. What if the air intake was located at the top of the firebox? There would be a chance that before it starts to draw, it could smoke out the intake.. Though once it gets going, it might help keep the box clear.

??

[joe]

I have checked out peterburgs heater, and his test results seem to show that it would be difficult to get any better in terms of efficiency. However, if my design turns out to burn efficiently, I think it would have a couple of advantages for the right user.

The firebox, which I estimated would be about 24" to 30" long, can accommodate much larger pieces of wood, saving the user time preparing the fuel. Ideally, even branches collected from a forest could be used as fuel. Even if cordwood is readily available, you still have the advantage of getting twice the fuel into each load.

The second advantage would be not needing the pipes to supply air into the fire, which I am skeptical of. Wouldn't they deteriorate rather quickly inside the firebox?

The reason for the height of the firebox is because I wanted the loading door higher than the 6" to 8" heat riser entrance, to make loading easier. In this setup, any smoke that isn't swept into the riser by the incoming air supply will quickly move to the highest point in the firebox. The extra headroom in the firebox gives a buffer zone for smoke to build up before it slowly gets siphoned out by the small slit above the heat riser entrance. I suppose the firebox is still rather high though, and could probably lowered to just above the small slit.

I'm doubtful about having any openings into the living space at the top of the firebox...if the firebox is any larger than the minimum system diameter, there won't be enough incoming air to wash all the smoke out of the firebox. Even if the entrance is perfectly sized so that the air supply itself is blocking smoke from escaping, at some point the stove might start drawing less due to coals building up or something, and some exhaust might find its way up into the living space.

Anyways I think I'll try to build a small version of this stove to heat a pot at the top of the heat riser and see how it does. Thanks for the input!

[Donkey]

.. Good thoughts, I think yer right about air intake towards the top. Still, I have my doubts about the firebox configuration.
Really, the way to find out is to build it and see.

I'm looking forward to your results.

[joe]

Here is a simplified version of my design to better demonstrate how I envision it working. This version is also probably a lot more practical to build.



A small kindling fire gets lit as far in as you can reach, then pushed to the back with a longer piece of wood.
The heater gets loaded with horizontally positioned pieces of wood stacked right up to the middle baffle. The heater is about 40" long, so 24"- 30" pieces of fuel could feasibly be used.

[Donkey]

I think I'm understanding your concept a little better now.

I'm assuming that the first vertical run will be an insulated "heat riser"..

What's the purpose of the middle baffle?

[joe]

The middle baffle isn't really necessary, but I'm hoping it will contribute to a cleaner burn. Initially, when the firebox is loaded with wood, it will help direct incoming to the top of the firebox, bringing some of that excess smoke down into the burn zone. Later on, once the fire is burned down, it will also help direct incoming air against the bottom of the firebox, fanning the coals and keeping efficiency up until the burn is done. Will it really work? Who knows?

The first vertical run is intended to be the heat riser. I'm hoping that a straight firebrick heat riser will heat up and start the draw fairly quickly. The rocket/bell built at the workshop I attended had a 4' tall, 7"x7" heat riser built from firebricks laid on their sides. The stove was easy to start up, but smoked back a few times until we built a proper chimney at the exit. After that it performed very well, though we weren't able to measure the efficiency.

[peterberg]

joe,
Honestly, I don't think it will work. It looks like an old-fashioned "grubka", a Russian masonry heater. The only differences are the baffles and the height of the fire box.

It isn't a rocket stove with horizontal feed either. That one should have an elevated shelf with the wood on top of that. The majority of combustion air has to pass under the fuel in that situation.
You'd stand a fair chance to get it working if you'd decide to extend the middle baffle to the bottom of the fire box. In that layout the flames are going down behind the baffle. That leaves the problem of getting enough air in the top of the fire box. Preferably a short distance in front and above the baffle.

Of course, you are fully entitled to build the thing and test it. Probably it would work, but in case of good (properly measured) results I would be surprised.

Just my two cents worth.

[berko]

Sorry, but i can't see pictures ... img101.photolava.com ....
joe
... fix it please ...