jacob green

Maybe someone with experience can verify this for you, but I think you will want less pressure on the back end of the system to help gasses move through the system.

Especially if you will be having such a constricted system.

maybe 4 inch exhaust would be good, and that also happens to be a real stove pipe size, so finding suitable material would be easy.

The only thing I wonder about by your description, and maybe my lack of knowledge is making me overly cautious, but if your stove doesnt move air through the system, and you try and start it up cold, so you got a cold stove, starting with a really cold burn and not much is happening, I just hope woodgas type of vapor does not accumulate in your tank while fire is smoldering/ going out. Then when you try and light the stove it causes a problem.

The lack of insulation and tall riser combined with your tiny system diameter it seems like there wont really be much physics to move things along in your system.

There does not seem to be much of a "heat pump" effect. Without the space in your tank being cooler than the air going up your riser, what will suck the air along?

The stove works on pressure differentials. I am not sure your system will have any.

maybe you can build a mock up without welding it first and see what happens.

Dont forget to add the exhaust in the mockup and see if gasses will move all the way through and out the chimney.

Dan Henn wrote:Hey all,

I figure it's worthwhile to experiment a little, maybe even use the heater in my fishing shanty until I burn it out.

Which, the heater, or the shanty?

: )

You mentioned it being a cool woodstove. Part of what keeps a woodstove "safe" is that the so much hot air is exiting the system that it carries with it any toxic/explosive gasses.

I have not built a stove yet, but I have been doing quite a lot of research, and the thing that concerns me most about trying alternative designs is that they have not been tested by anyone, so basically, I would be the guinnea pig.

Building an experiment that doesn't work will aid in your education. Building an experiment that injures you or someone else I suppose is a type of education too.

I saw a guy on youtube who built what appeared to be a functioning 3 inch heater in a tank of some kind, but he used a lot of the tested principles of RMH. He insulated the feed tube and burn chamber and riser really well. He mentioned that he initially planned on using just use steel pipe, but decided to use firebrick instead after so many people warned him away from the steel pipe.

His design also had a REALLY tall riser. Much taller than your propane tank would allow.

He also was following formulas from Ian Ianto's book pertaining to the areas of the different sections of the stove and how they should relate to each other in order to keep the stove functioning safely.

His stove APPEARED to meet the minimum requirements of functioning safely, but probably would not fare so well if tested for efficiency.

Since I am new to the math, and have no experience, I dont want to advise you on any part of your build. But definitely look in to exhaust ratios, you don't want a constricted airpath. Hopefully the worse case scenario is that your stove just wont work, or will function as a smoke generating device.

In any case, it doesn't hurt to do lots of research before you build anything.

You can learn a whole lot by researching before you even touch your tools.

Dale Hodgins wrote:   
    The plan is to build a U-shaped sheet metal slide which is set about 10° from vertical so that long lengths of firewood will lay straight and automatically feed into the rocket stove.

Hello Dale.

Did you ever try this?

What kinds of variables did you encounter?

Len Ovens wrote:

Do you have a specific application in mind? What size/weight are you designing for? I have thought of small scale rocket heaters, but have not had the materials/money/time to try my idea out. Personally I would try to include some mass in the form of soapstone or cast iron if nothing else. These are denser materials than cob or even fire brick and so would store more in less space.

A couple applications. One would be any type of livable vehicle from small to large motorhome.

Another would be anywhere one might set up temporary camp, such as fishing expedition, gold panning, etc. Small lean to situations. Occasionally there is a need to spend some time in a small one room cabin. etc.

One of the ideas I had was to fill an 8 foot, two inch diameter tube, laying horizontally, or slightly diagonal, with pellets/twigs and figure out how to make the fuel burn very slowly along the entire length of the tube, so that about only 1 inch of the metal would be getting hot at one time. The entire tube would either sit horizontally, or diagonally, and function as the feed tube, burn tunnel, and riser ALL IN ONE straight pipe. Or it could have an additional 3 foot riser on one end to create draw. One could bury this in dirt under a sleeping bag or cover with dirt on the side in a lean to. But now I understand rocket heaters better, so I know there would be no way to get hot enough burn to be efficient this way.

But that's just to give you an idea of how radical some of the directions I am exploring are.

Possibly if I could figure out how to burn the resulting woodgas at the end of the system with a small chamber it might work. Either way, I would not want it to accumulate wood gas and create a pipe bomb right next to me.

maybe I could start a fire at both ends of the 8 foot tube, and the at least the woodgas from one end would have to travel through the fire at the other end to exit the system.

Len Ovens wrote:
(Re)movable mass is another interesting idea.

on the 8 foot tube stove I had an idea to have semi-circular cement drain tile underneath the tube, then cover the tube on top with several pieces of the same material to complete a cement jacket around the entire burn tube. Because it would quickly get too hot, then the cement jacket would simultaneously block the extra heat, while storing it for later.

Or when the space got warm enough after initially starting the fire, I could cover with dirt and rocks.

Regarding the normal 4.5 to 6 inch RHM with small mass such as over an existing fireplace hearth. For portability I wanted to try 5 gallon cans filled with water, stacked very close to the barrel and vertical exhaust. I figured for a small space they would block some of the initial heat that would be too hot for small space, but would absorb plenty. I could get 10 5 gallon cans stacked two high around a 20 gallon barrel and vertical exhaust leaving the front of the barrel exposed to direct heat. The cans could simply be emptied of water, and with lids off they would stack and be very light and take up very little space. I would either leave holes in top to vent if they got to hot ( which I doubt they would, or create a system of tubing to vent outside if it was creating a steam problem in the space.

Len Ovens wrote:
I was going to suggest using a gasifier set up next... it turns out that is what the Kimberly is

I am starting to think this is the only way to achieve a very small volume fire, and at very slow speeds, and have complete burn.

That is another one of my objectives to meter the fuel out VERY SLOWLY. It does not take much heat at one time to take the edge off in a very small space. And metering out heat very slowly is contradictory to a complete, efficient burn rocket style. But since gasifying works by INTENTIONALLY making a very slow, cold burn, one can achieve a much smaller btu per hour, while simultaneously extending burn time.

Which for small spaces is perfect. Because if one does not have the MASS to accumulate the energy from a very fast, hot burn, the only other option is to slow down the burn to achieve a the goal of not having to constantly put fuel in.

Unfortunately the gasifier setup seems a lot more scientifically complex. Where as I got my mind around the physics of a rocket heater very quickly, I am not certain what is required to build a kimberly type of gasifier.

The guy in the video with the motorhome did mention that at the top of the stove was a "honey comb" thingy, which I can only assume is a catalytic converter, which would make sense, seeing as how the fire is being metered out so slowly and with such a cold burn, that the exhaust is mostly wood gas.

I have to admit, that playing around with woodgas in chambers, seems a lot more technical, and critical, than achieving a quick clean burn based on the simple physics in a conventional RMH.

But there cant be that much to how the kimberly stoves work, and at $4,000 there will probably be a lot of motivated people trying to figure out how to build a reasonable facsimile.

Len Ovens wrote:
so the highly efficient iron stove in the lab becomes another 10%er in the home where it is run at an idle/smolder.

Len Ovens wrote: and cut the air flow till it smolders along nicely. Six months later when they have a chimney fire

My question specifically eliminated that eventuality. To make sure I am clear, having a "smoldering" fire is not my intention. I indicated that I completely understand why incomplete combustion would result in creosote, and in turn, flue fires.

"To clarify, if the riser is the same heat, and the barrel is the same heat, and exhaust leaves the house at the same temperature"

What I meant by that was the the fire would NOT be smoldering. The main thing which attracted me to rocket heaters in the first place was the complete burn, and videos of people showing how only steam and C02 was exiting the system. So for me, if I am not getting complete or near complete combustion, I am not interested.

Len Ovens wrote: you take away the mass and you have an iron box that can not (except for testing) be run at full efficiency without over heating the room.

If a smaller volume of fuel was on fire, then the fuel could be burned at full efficiency, and the room would not overheat,

Len Ovens wrote:
So just remember not to call it a rocket anything so those who are working on the RMH don't get blamed for problems with the iron box stove that gets built.

Do I have your permission to at least call it a "Pet Rock Stove", or is that too close to "Rocket"? How about "Racquel Squelch"? ( cold burn, not-rocket sound ) : )

Len Ovens wrote:It is not that design is flawed and won't work without mass, just that it is not appropriate for home heating

My interest in non-mass rocket stoves is not for heating a standard home. In a standard home situation I would MUCH rather have a large thermal mass radiating all the time.

In small spaces however, mass, starts to become a problem. Either because of space, or because of weight.

My nature is to try and figure out new solutions, and create new things. Sometimes I succeed. Sometimes there is no room for improvement. Occasionally dogma bares it's fangs.

Have you seen Kimberly Stoves? I saw a video of a guy who had one in his motorhome. Looks awesome. The webpage says it burns for EIGHT hours on one load. Cool, where do I sign up? I would just get one or two of those, except...they are almost 4,000 dollars! Yikes.

The Kimberly stoves I have seen have no mass. And to complicate matters, it is also an Iron Box, well more like a Steel Cylinder. Both descriptions would be equally suitable as 80's metal bands, or porn titles, capitalization was an after thought.

Either way, the stove has no mass, and does not appear to be prone to flue fires. And I am not naive enough to believe that advertisements are real life, but the people enjoying the stoves don't look "edgy" at all, in fact, they look quite comfy. : )

So I was just trying to figure out specifically what aspect of massless designs would cause flue fires. I was not sure if the point was that the exhaust came out a lot hotter, or that the mass itself could tolerate an internal creosote fire, or both.

I have several designs for wood and pellet burning stoves I am working on, a couple don't even resemble RMH in the least. And I am DEFINITELY planning on building one or more RMH stoves in the mean time which follow the known and trusted methods as close to the letter as I can. The current design is brilliant, and brilliantly simple, and I definitely want to know how to build the current design as a LIFE SKILL, and as something I can always fall back on, which I know from other people's experience, will definitely function and function safely. And I am gathering as much information as possible to help with all of these processes.

Constructive input is much appreciated!

: )

allen lumley wrote: so there is little room for gain!

This is what I wondered about. It seems that the conventional RMH is very efficient as it is regarding the maximising of fuel burn.

Also, the inner dimensions would need to be completely altered to accommodate the extra drag from the converter, so clearly it can't be tried on existing functioning rmh's.

The other downside would be that one of the most valuable aspects of current RMH design is their simplicity. Designing an RMH to accommodate a catalytic converter would ADD variables. And my general approach is that it's better to go with solutions which have fewer variables. Also the converter would wear out, so it would also be a part that needs replacing, and a part that is not easily manufactured DIY.

But still it sparks my curiosity just because it's a different WAY to burn the leftover gasses, so I wondered what would happen when combining two different methods to process the same effluent.

But it's probably a pull yourself up by your own bootstraps type of fallacy. It would probably alter the flow to such a degree that what happened at the barrel would no longer be as efficient, thus countering any gains achieved by the converter.

Satamax Antone wrote:It would burn!

What if it was high up enough to where the flame didnt touch it directly?

What would happen if a catalytic converter was placed at the top of the riser, before the barrel?

would this burn more off the unburned gasses?

Any thoughts on this?

I was wondering if anyone has ever experimented with something like a basket ball size sphere inline about half way up a 6 inch riser configuration, then closing back down to the 6 inch riser diameter for the rest of the riser.

or possibly more than one sphere in a line in the riser.

Or possible different shape like a toroid.

I was wondering if this would create a low pressure zone(s) that would cause the unburned gasses to slow down and mix around in the chamber, and also a super heated flame would be shooting right into the slower gasses possibily helping to combust them?

I understand this is essentially the effect the top of the barrel has. I was just curious if closing the diameter back down again, with a ratio of dimensions that would still keep the airstream moving through the riser would have any kind of interesting effect.

Anyone have any thoughts on this?

Ok. Thanks cindy and charles, I understand now. : )