A simple device to retrofit standard j-tube to burn pellets, resulting in less fire tending.

I watched some videos with an excellent rmh design that used a self feeding pellet chamber to "automate" the feeding of pellet fuel in to a rocket mass heater.

To accomplish this, the designer built a permanent trough for the feeding of pellets.

This got me thinking. Has anyone ever tried just filling a metal tube (8 foot downspout for example) with pellets and putting one end down in to the j tube of a conventional RMH?

One would not want the pellet tube to become a chimney, so the portion of the pellet tube which feeds in to the j tube would need to be equipped with some kind of mesh or perforated material that would allow air flow at the opening of the j tube, thus negating any/much heat trying to go up the pellet tube. Built in to the bottom would probably have to be an attachment which provided a grate for pellet ash to fall through.

This idea seems more ideal with RMH that have a diagonal feed tube rather than a vertical one, but who knows.

Also this idea would really open up the functional possibilities of smaller rocket heaters possibly made entirely from metal, thus eliminating the need for thermal mass to keep producing warmth after the fire goes out.

What would be cool is to figure out how to make a 2 inch steel gutter filled with pellets feed a small portable stove in a small space for 8 hours of sleep time.

Also what would be cool is refueling the stove only THREE times in a 24 hour period. Thus being able to leave for 8 hours at a time with out the fire going out.

I have only seen a couple RMH that incorporate pellets, and the entire inlet for the RMH seems to have to be designed to incorporate the burning of pellets.

There must be a simple retrofit for people who already have a conventional RMH but want to burn pellets.

This idea would be convertible and would allow easy switching between burning pellets, or the standard twigs/ sticks fuel etc.

Any ideas?

Comments?

Haters?

: )

P.S. this general concept applies to burning normal twigs sticks as well, however more variables come in to play seeing as how the fuel is random and not uniform.

I have never seen anyone discuss how LONG the sticks feeding in to the RMH are. Obviously a stick which is twice as long will need to be replaced half as often as a stick half the size. And a stick FOUR times as long will burn FOUR times longer before being replaced.

There may be a way to load sticks/twigs in to a similar device, but it does seem that various elbows/snags in the natural sticks and twigs could get hung up while falling down the tube.

And another variant that comes to mind would be to DESIGN/manufacture "perfect" single long runs of compressed fuel to feed in to the j-tube.

How about a SINGLE 6 foot by 3 inch compressed fiber fuel pellet that will self feed in to ANY standard RMH?

This also opens up the possibility of using even SMALLER biomass such as grasses etc. It probably would not be to hard to figure out how to compress and extrude a single long fiber log that is optimized for feeding in to RMH systems.

Any ideas and comments are welcome.

Pellets, by their nature, have a lot more ash than cord wood. Moreover, they have some amount of embedded energy because a machine somewhere else had to make them. They are very uniform, so what happens to all the material (such as bark) which doesn't match the color the pellets are supposed to be?

Also, the point of the mass in a rocket mass heater is the same as the masonry materials in a masonry heater. You burn fires to heat up the mass of cob or the mass of fire clay bricks and then you don't have to tend the fire all the time because the mass is still giving off the heat. The colder it is outside your house, the more mass you need to absorb heat and then radiate it back to you. The insulation of your house also figures into this. If your house is well-insulated, you won't need as much mass as you will if it is not.

Cindy Mathieu wrote:Pellets, by their nature, have a lot more ash than cord wood. Moreover, they have some amount of embedded energy because a machine somewhere else had to make them. They are very uniform, so what happens to all the material (such as bark) which doesn't match the color the pellets are supposed to be?

Pellets can be made from a wide variety of pulpy biomass. They are not even difficult to manufacture at home. They use up the last of the scraps from manufacturing and construction process, woodworking, etc. I am not concerned at all about the color of my fuel pellets, so I have no aversion to bark and all being used to make pellets as long as it burns.

Cindy Mathieu wrote:
Also, the point of the mass in a rocket mass heater is the same as the masonry materials in a masonry heater. You burn fires to heat up the mass of cob or the mass of fire clay bricks and then you don't have to tend the fire all the time because the mass is still giving off the heat.

If one had an easy method to automatically feed a small combustion device with fuel creating on demand heat for 8 hours, the entire design and mass of a RMH would hardly be needed. All of the clay, cob, brick, and barrel could be eliminated creating a totally different animal, with different functionality.

Keep in mind that RMH with huge thermal mass cob bench is not practical in tiny spaces, for camping, for trailers, or for moving from the living room into the workshop, etc.

This addresses a different function than the ideal way to heat a standard home. For a standard home application, I would rather have a large thermal mass always radiating.

But even in that situation, some kind of 6 foot fuel that fed itself into the burn chamber so the fire could be unattended for 8 hours would be nice. What if all you have is a bunch of 1 foot twigs? How often would you need to be replacing them? Surely a 6 foot piece/pieces of fuel that fed itself in automatically would require less fuel tending.

also if the fuel was always occupied a uniform space in the inlet tube, would that allow for new modifications to RMHs which precisely dial in air intake and exhaust ratio.

One thing that RMH/rocket stoves do not currently have is any kind of "dampening" function.

The air intake and exhaust is always the same opening, the only thing which alters flow in an RMH/rocket stove is how much fuel are you burning at one time, and or how packed with sticks in the intake opening. There really is no way to adjust the air fuel mixture to slow down a burn, to lean the mixture, or to conserve fuel etc.

I think the current design and functioning of RMHs are excellent, these things I am proposing simply add to the current functionality that already exists, they do not supplant it.

Hi Jacob,

I think web4deb Rob has made an excellent pellet feeder for his rocket stove.

He can also switch from wood to pellets and back quite easily.

I have been looking at the same problem. I want to build a rocket stove that can burn pellets
as well. Only, I want to be able to start up the rocket stove automatically. Sometimes I am gone for a
few days and then the temperature in my greenhouse would get too low (for aquaponics)
After seeing one of Rob's videos where he says that he pours a little diesel on the pellets to make em light up
faster, I am thinking of constructing an automatic fire mechanism with an injector that squirts a little
gasoline onto the pellets and ignition with a spark like from a gas heater. I don't want to use propane
gas in an unattended situation.
I think a little tinkering with an arduino, a few sensors and a few dc motors, I'd be able to accomplish it.
I am just brainstorming here off course. Maybe someone else has found the perfect solution already?

Jef

I think a hopper above the feed tube that allowed pellets to drop in, but was not actually connected to the tube and not so close as to interfere with air flow, might provide the desired feed without making a chimney that would lead to smoke back. Working out how to have the pellets drop from the hopper into the feed tube without overflowing, etc. would be the challenge.

I would not want to use long continuous fuel rods, in part because I have visions of them burning upward and falling out of the tube, rather than nicely dropping into the feed tube. I have frequently experienced fuel that has "hung up" in the feed tube and needs to be pushed in. Gravity does not always address the issue.

Constant feed rocket stoves would definitely be a different animal than rocket mass heaters, and as such involve a whole different set of parameters.

As to the idea of dampening the air flow - seems to me that adding that feature changes your stove from being a rocket stove to being a conventional variety of stove. One of the defining features of the rocket stove is that it burns as hot and clean as possible, and dampening runs directly contrary to that ideal.

Peter Ellis wrote:

I would not want to use long continuous fuel rods, in part because I have visions of them burning upward and falling out of the tube, rather than nicely dropping into the feed tube. I have frequently experienced fuel that has "hung up" in the feed tube and needs to be pushed in. Gravity does not always address the issue.

.

Hi Peter,

It looks like Rob has done a good job with his pellet feeder. It doesn't look like he has problems with the fire traveling back up the
feed tube. Here is a link to his Rocket mass heater on pellets:



All the best, jef

Jeff, my concern was directed toward the OP's idea of using 8 feet of downspout to feed pellets. I have concerns that such an approach would turn the downspout into a chimney loaded with burning pellets.