enlarged firebox

Hi friends
Kevin here, and I've been following many threads, and post on here, trying to take in all the information I can before attempting to build my own RMH, so this is my first post! I've seen many post, and comments, about tending/feeding the stove, and read many possible ideas, but the only idea I haven't seen yet, (and please correct me if I'm wrong) is an enlarged firebox! I can't imagine Earnie, and Erica have not tried this yet, as it seems they have encountered everything there is with the RMH...My thoughts are, if you could make the firebox large enough to hold say 3 to 5 standard size log quarters, but have a cover that has the original size opening in it to allow air to flow through it, to cover the wood. A cover with a hole in it essentually, and the fire tube, and heat riser would be the same size as usual! I would believe that this may enhance the turbulance, due to bottle necking, and increase the overall burning temp, since the bed of coals would be larger giving an overall heating surface. Has anyone seen a post on this yet, or heard of anything like this, and if so, how well/poor did it perform?

I would be afraid that the cover would create dead spots in the air flow and then you would not have the desired turbulence. What you really want to know is how will scaling up the RMH in size affect the Reynolds number of the air flow through the RMH. Now I know just enough about fluid mechanics to be dangerous in this regard, so I'm not going to guess if the Reynolds number will go up (more turbulent) or down (less turbulent). What I do know is at putting a cover over it is going to change the cross-sectional area that is drawing air.

If you really want to understand the fluid dynamics of combustion inside the rocket stove and get some ideas, have a look at this PhD thesis entitled Breeding a better stove: the use of computational fluid dynamics and genetic algorithms to optimise a wood burning stove for Eritrea.

John, Thanks for the info! I'll be reading it tonight, and will get back to you!

You can find working models of your depiction at these forums http://donkey32.proboards.com/ called horizontal batch heaters. They work fine. There seems to be a big behind the scenes political fight against the L or batch burner box just because it's some thing new and perhaps better. That nasty fight was mentioned on the 4 DVD set. That happens in all areas of design with the mostly unspoken words don't you dare change what's already been done, it cant be improved one bit. I'm a way out of the box inventer and get hit with that statement all the time. I am going to do what you said on my rocket bell heater. There will be an opening on the top of the burn tunnel equal to system CSA. On the end of the burn tunnel there will be a large glass door to put in longer pieces of wood. It will be both L and J burners ! LOL Ready for a little political flack. LOL Alan

Thanks for the links Alan, I'll take all the info I can get! As for the political flack...I work at a factory of union workers, so I'm quite used that! Political garbage is second nature around this place!!! lol... Thanks again for your input my friend!

Kevin I will give you another big hint on how to easily make the big burn box. I have watched quite a few vids on YouTube on how to build pizza ovens and masonry stoves. They both use an arched top burn box for size, strength and long term use. Create a curved wood form out of very thin bending plywood and use it to form your arch. When the mortar dries pull out the form. The hole in the back wall into the riser will be system CSA. On the entry you can have a rectangular or partial rounded door on top. I haven't got that far yet or I would show pictures. This is the path I am going to take.

On DVD 4 Hot Rocket starting at 16:36 Ernie, Erica and Paul Wheaton compare the L tube and J tube design. They said there was a big fight between the J and L groups to the point where a contract was drawn up that each group could only work on their design version. Paul called the L tube a lesser design. With that being said since the above 3 run these forums I believe this site is the strictly J tube only group and you will never get an accurate, unbiased view of the horizontal batch heater here. For that go to the site I mentioned before. This is very sad but the truth of the whole matter.

Alan M.

I don't believe their is any conspiracy to suppress technologies. In my limited view RMH are a DIY essentially open source technology. I see many members contribute on both sites. To me their looks like a great cross pollination of ideas and a willingness to help do-it-yourselfers on both sites.

Bill

Thanks again Alan for your info, and input!!! I personally fail to see the difference between the L, and J designs, unless it's a matter of turbulence! I believe that in either design that the meat, n potatoes of the units, are in the tube, and heat riser! Although, I do not have Ernie, & Erica's years of hands on experience, but I have done some trial n error of my own, with both designs, with quite similar results, according to the test equipment I use, which is none other than my "finely tuned" eyes, ears, and nose! lol... All joking aside, I think they both are great designs, and both produce excellent results, so I think that leaves us with personal prefference! "PERSONALLY" I preferr the J design, simply because it's self feeding, I just want to expand on the self feeding design!

I think the issue is not so much having to do with L v J, but more Ianto Evans v World. As for the horizontal batch feed rocket stove on Donkey's forum, it has greater similarity to the RMH than to the Aprovecho Rocket elbow stoves.

Designs need to be adjusted, no matter how proven they are. Every installation has its own peculiarities that must be dealt with. It is easier to make those adjustments if you aren't changing other parameters unnecessarily. If you want to experiment, and I certainly encourage it, don't do it on a permanent installation, and don't do it inside unless you are properly equipped for it.

There is a downdraft batch feed design that might be adapted to the RMH, Richard Hill's Stick-Wood Furnace. Take special note of the comment in the last paragraph on page 4 regarding explosions.

Andrew Parker : Due to the crude testing devices of that period and Prof Hills necessarily hairy wild ass guessing of what his instruments were actually telling him, not too much
should be made of thisDesign !
However the fact that it parallels some of I.Evans' early work, and did see production in both Maine, and Canada is just one more nail in the coffin of those naysayers who refuse
to accept Rocket Mass Heaters as "Real Heating Units !

There are a few people here at Permies playing with them, you can go to the Permies tool box at the top of this page, click on search, and do a google search here in Permies to
find them, Another way is to look at the bottom of this page, in the Similar Threads section ! Big AL !

Allen,

I only made reference to Hill's design as it regards his vertical batch feed for conventional stove wood, which perhaps, maybe, might be used with an RMH, with significant modification. I don't know if an RMH would provide enough draw to negate the use of a fan, and there is the backfire issue to deal with. The horizontal batch feed seems less complicated, but if someone wants to experiment, let us know how it goes.

Andrew, and Allen, thank you both for your information, and opinions! I think there could be possibly thousands of design modification to the MRH, and each one would have it's place depending on it's intended use! One then I DO see, is that we almost unanimously agree that designs for cooking purpooses, are not that good for heating purposes, and visa versa! I have finally collected all materials needed, to begin my experimental design, and even got in touch with a local university, who is (hopefully) going to provide me use of testing equipment, so I can give some acurate feedback on our findings!!! I have also spoke with a local glass manufacturer. My idea with the glass is that I can use it on one side of the stove, so we can actually SEE what is happening inside the stove while it's in operation, along with the test equipment! I'll keep you all posted!