DSR 2019 build

Well, a new heating season is begun and with it a new iteration of the previous Rocket stove, called a Double Shoebox Rocket.

The group over at the Donkey forum did some experimentation back in 2018 coming up with this concept, which was later abandoned by Peter van den Berg, the chief experimenter on the project, as being too unreliable.

By the time he had moved on to a different design I had already started building, it was getting colder, and looking at the elements that seemed to make the DSR run away with the burn, they did not seem as relevant to my design, so I just continued to build according to his best guess dimensions.

My 2018 build used a number of walls that were simply formed of clay, or a clay perlite mix, and a couple of the sides around the water tank were taken from an old washing machine, with some fiberglass insulation hastily fastened to the inside of the walls, with clay slopped around the top and edges to give a seal.

The door to the burn chamber, as in many projects done on the cheap was a problem until I finally bought a couple pieces of neoceram stove glass, which cost more than all the previous stoves from the last several years.

While this new glass has proved very durable, having a door that really is robust requires more than just a glass pane, so that is still in the development phase, although I’m pretty sure I have a workable solution which will likely happen sometime during this season. For now I continue to get a potholder if the glass is hot, and as gently as possible remove it and then wedge it back into place.

The other main change is the use of bricks to give a substantial continuous exterior that is well sealed and even looks a little better.

One other important note, my exhaust was set up for a low temperature ground level “stack” and to use the push of the j tube rather than the pull of a draft. Since the first batch box conversion about three years I found it necessary to install a fan at the end of the exhaust pipe to aid with the draft. This totally eliminates smoke at start up and keeps the draft more even.

while it may appear the smoke is being pumped into the ground, the downward tube is actually wide open at the seam, this arrangement helps prevent sudden gusts from totally disrupting the draft
The brick exterior is continuous back to the poured concrete wall as I continue to remove clay from the previous construction. the removed clay goes right back into the new build
note the wet perlite clay mixture formed in place around the DSR core. The stack/exhaust is on the floor at the right side of the shovel
the clay perlite insulation layer continues across the concrete wall in back
The second chamber is now well defined and the brick courses are starting to grow
Note the rectangular passage on the right where the exhaust comes in to the first bell from the secondary burn chamber. The rim of the duct to the water tank “bell” can be seen just opposite this entrance and further down in the chamber
The right side of the water tank shows the location of the duct from the first bell just visible above the top of the front bricks
overall layout of stove. note exhaust moves from right to left through the chambers and at the bottom of the water tank chamber it turns back and flows under the construction to the exhaust “stack”
salvaged glass stove tops are sealed with wet clay to the top. Note the left side galvanized pipes exit and the blue pipe insulation for the hot water outlet
proof of concept, the first fire verifies the exhaust, now the drying process begins
looks just like the pictures I saw when I first started last year, note that the bricks are joined with a clay “mortar”, if I want to rebuild, everything is easily recycled with water as the solvent
I usually have a small piece of ceramic fiber board over the glowing section of the stove top. Temperatures are way hot, and after passing 1000 degrees F it just registers as “HI”

cooking can be done here, very carefully, but I like the idea of more insulation to increase efficiency of the burn. The second chamber still has plenty of heat for a more reasonable cooking surface, and even the water tank chamber can keep things warm
with the top cleared and clean

DSR update 12/25/2018

The double shoe box rocket is elevated off the floor about 18 inches, and instead of an exhaust on top- in front, it is channeled horizontally under a glass stove top from left to right.

Having the water tank inside the bell was an idea suggested at http://donkey32.proboards.com   that led me to my design, which in appearance is like a glass stove top, with an extended simple porcelain covered metal counter top.

This extended bell houses a naked 20 gallon water tank with two fittings, one for cold water at the bottom and one for hot at the top.

The top fitting connects directly into the hot water feed for my house system, and while in operation the hot water valve to the shower head in my tub is left open, and the cold water flow to the tank is shut off. This allows excess pressure to escape safely, and notifies me when the water is hot as steam starts to escape. Note that this is primarily proof of concept, and not yet ready for prime time water heating, it could easily have safety features added that would further ensure a more automatic type system.

note the new visions fry pan  “door” to the batch box, The lid I was using had broken into two pieces possibly from rough handling, possibly the lids are not as thermally  robust as the pans

Last night I was burning the third batch of wood in the firebox,low grade poplar and some mystery wood, likely not completely dry, when I started to hear the steam. That produced a luxurious long (10 min at 4-5 gal/min), very hot shower (mixing lots of cold water). I was concerned about stratification, and the possibility that all the water would not heat evenly, but the length and relatively constant heat of the shower indicated this was not an issue.

The design inside takes the combustion gases exiting under the stove top into a very broad vertical opening that directs the hot gases forward into a circular motion around the whole vertical surface of the tank, with some small horizontal space over and under the tank. These gasses that are further cooled start to sink to the bottom as they circulate. The “stack” entrance is below the bottom of the tank in back of the system, so the exhaust comes in contact with about 270 degrees of the surface of the tank, with some minor contact top and bottom. Note that this stack is actually a powered exhaust by a very cheap, low wattage (about 10)fan. This provides a more or less guaranteed exhaust even at startup, and the exhaust is so cool (around 100F) that more robust (and expensive) equipment is not needed.

The test run last night reached temperatures on top of the port between 900 and 1000 F during the third batch of wood, with a very robust secondary burn at the port. Without testing equipment I have no way of knowing just how clean this is burning, but it appears that the system gets more efficient into the second and third batch of wood by the size of the secondary burn. Perhaps using insulated Fire brick at the port would get the port to temperature more quickly (it is currently standard , full fire brick), and adding ceramic fiber blanket over the stove top might also enhance the temperature build up by reducing convection and radiation losses there.

 

more DSR pics (double Shoe-box Rocket

Note the opening to the left of the tank, exhaust gases travel counter clockwise around the tank once the insulated top is installed

Two water connections to the tank, hot through the upper pipe, cold through the pipe that exits the enclosure botom

 

I prefer to think of the junk you see as a parts depository, the stove pipe comes up in the center of a poured concrete 2′ wall from the basement, runs horizontally, then down to the ground

The wider area of the pipe after the angle pointing down houses a small fan,

Though it looks solid from the sides, there is actually quite a wide openiong for the exhaust to exit. This configuration keeps the fan dry, allows for a small amount of falling for the exhaust as it cools, and protects pretty well against strong wind

 

sThe tank enclosure has an insulated   top and sides, with just enough room to circulate exhaust around and over the tank to transfer as much heat as possible to the water.

New iteration of the old rocket stove

Hello again from winterland– no snow but plenty of cold, it has even gone down below 20 degrees F already. Inside, the lowest it got was in the mid 50s.

With a new stove build in progress, the place has relied completely on sun for passive heating, and yesterday, the first full sun in several days, I even got out a fan, and was moving the warm greenhouse air into the bedroom. Needless to say the sun gave me lots of surplus electrical energy with the new solar array I installed about three weeks ago.

this project is pretty ambitious, a smaller footprint and less passive mass, but with some luck the   water tank will provide an active absorption and transfer of heat to the mass of the floor.

For now the plan is to use a naked water tank, but depending on how well it works I may look for additional transfer with copper tubing instead.

Last night I got the stove ready and did a small test run to make sure I could count on the exhaust fan, and there was no trace of smoke inside. I prefer to have everything completely airtight so even though  the system is not finished, with positive ventilation it is tight enough to start the drying out process. There was very little heat at the exhaust pipe outside, but at this stage that really doesn’t tell anything since lots of btus are needed  to dry it all out.

Once dry the  btus will be available for cooking and heating water. One other effect of the moisture   is the secondary burn chamber did not function very well, at least I hope that was the issue. I noticed a brief period during the burn when it started to ignite so that was a good sign,but most of the burning occurred in the firebox.

So while more insulation is needed, and the water tank needs to be plumbed in properly, for the time being I have a cooktop, and can continue the drying process.

 

Here’s the build history thus far

take off watercoil,remove rocket barrel, notice soot–wasn’t burning too clean (except inside the riser, which was still snow white. The batch box I installed last year was made for a 6″ riser, but lining the 8″ riser with “1 inch” ceramic fiber reduced the riser size too much. There also may have been an issue with the port configuration and the way I typically ran the burns.  Getting used to the batch box dynamics requires a new mind set over typical managing of the burn in a regular wood stove.

gone with the old and a new platform  in it’s place note that I’m working here with wet clay in forms a mock up of the batchbox floor with secondary burn tube. This is the tube I took out of the old batch box, but the new dimensions doubled the  size of the tube I had been using for secondary air supply–this may have been part of the problem with excess soot in the old unit Perlite and clay on the back and left side, refractory cement on the right (shared side with oven) . odd bricks and such inside and out are used as wedges to hold split firebrick liner in place as forms while the clay perlite mix is solidifying

Adding the top secondary burn chamber.

In this picture the floor of the top chamber is ceramic fiber using a bit of water glass as a stiffener, but the final solution was giving a slight slope of the firebrick in the lower batch box reducing the width at the top by approx 1/2″  and precariously using the 1/4 inch or so for support of normal split firebrick. These were secured with a layer of perlite and clay keeping them precisely centered. Picture of oven location

With the oven in place. The final configuration with baffles to channel the heat No door on the oven yet, but since the inside of the oven is outside the combustion gas area it won’t stop me from doing a test run, here’s the top gaskets made of ceramic fiber

with the stove top and water tank in place

finally with a hurry up enclosure around the water tank and the first fire, a power vent replaces a draft, and the vent pipe was just comfortably warm outside after a half hour burn

Follow up tests have raised the stove top temperature to 570 F as the clay dries out. Once the temps start to stabilize, assuming a strong secondary burn,  I’ll be able to more accurately test the effects of different baffle placements, and actual potential of the design.

      view of secondary flame through top

 

views of firebox

This was taking at the beginning of a burn cycle. During the hotter parts of the burn the flames are a continuous robust splash against the amber colored stove top glass.. temps here are just approaching 900F.

Please note  much of the fuel is a bit damp. this slows starting and reduces overall performance.

Rocket Stove Pics

testing outside, sand covering exhaust–that paint just won’t burn, maybe it’s high  temp:-)

Maintenance with a 100 feet of copper makes lifting a 55 gallon drum that much more difficult–notice the paint is gone, sealing the bricks of the firebox, better riser, higher heat, but that means citra solve paint remover and delays

replacing mud around base is an easy repair  notice the pex pipe connection just above the firebox

Exhaust returning from the bench going out of the house