|
|
Post by grizbach on Oct 14, 2009 13:05:54 GMT -8
Hi all, so I built a pocket rocket to see what all the hubbub is about. I'm hooked!
Anyhow, after two burnings I thought the fire would burn better if the air got preheated by the coals. So I popped a hole under my ash pit and put in a grate. It was a very noticeable improvement! Besides the preheating, the stack is made longer by not having the air pull down the feed tube.
Has anyone tried this before? I'm about to make a 5 inch space heater with a bottom air supply. I'm stoked! (pun intended)
|
|
|
|
Post by Donkey on Oct 14, 2009 19:07:10 GMT -8
Hmm... Interesting.
Honestly I haven't fooled with pocket rockets much. Built a couple but that's about it.
They're impressive, eh?
Though I should say that pocket rockets aren't technically rocket stoves. They share some features in common, still not exactly the same beast.
|
|
|
|
Post by grizbach on Oct 15, 2009 15:24:28 GMT -8
Though I should say that pocket rockets aren't technically rocket stoves. They share some features in common, still not exactly the same beast. Actually I'm building for the mass heater, but without the mass. I would like to build my drum out of aluminum for better heat transfer. Do you think the top would get hot enough to melt? If so, maybe I could have the sides aluminum? Donkey, I read the post on the stove you made. It's gorgeous! I don't understand your 3 ft. horizontal feed tube though. Could you explain please? |
|
|
|
Post by Donkey on Oct 15, 2009 21:14:47 GMT -8
I would like to build my drum out of aluminum for better heat transfer. Do you think the top would get hot enough to melt? If so, maybe I could have the sides aluminum? I wouldn't use aluminum.. I have seen temps high enough to melt it. Not sure how you would connect aluminum sides with something else (50 gal drum fer instance) for a top and get it gas-tight. Err.. Aluminum IS a pretty good heat exchanger, though it seems steel is good enough.. ?? Sure.. It was supposed to be a big ash clean-out/reservoir in the back of the stove. Turns out I can start a fire in it, get it going, shove it all the way forward and pack cord-wood behind it. I discovered that it runs best with the air intake constricted, so I guessed on the size and made a sheet metal plug-with-hole to close up the end of the (new) feed tube. Seems that I got the air hole sized pretty close (close enough) and it burns full out, as clean as ever. I suppose I should post images of the back side of the stove there.. I don't think I've done that yet. |
|
|
|
Post by grizbach on Oct 15, 2009 23:34:34 GMT -8
Turns out I can start a fire in it, get it going, shove it all the way forward and pack cord-wood behind it. I discovered that it runs best with the air intake constricted, so I guessed on the size and made a sheet metal plug-with-hole to close up the end of the (new) feed tube. Seems that I got the air hole sized pretty close (close enough) and it burns full out, as clean as ever. I suppose I should post images of the back side of the stove there.. I don't think I've done that yet. Wow, thats great! So you can get long burn times without a vertical feed? I have a lot of cord wood, this might be a design in my future! I wonder if we are experiencing the same thing. With my bottom air intake, the air is hotter/ less dense. So I am running a richer mixture. I find I can even close off about one third to half of the feed tube and still get a good burn. |
|
|
|
Post by Donkey on Oct 16, 2009 9:01:22 GMT -8
I can't really speak to the modifications on your pocket rocket..
I can say that I've noticed that rocket stoves (seem to) run best with about 1/2 - 1/3 air intake to system size ratio..
So-- Good observation.
It would be nice to pin it down a little tighter than all that. Though roughly right IS better than precisely wrong.
|
|
|
|
Post by grizbach on Nov 17, 2009 0:40:41 GMT -8
So I figure it's time for an update:
Before I start, It does seem that each and everyone's stove has it's own personality (no two are alike).
I've probabably had about a dozen fires now and I feel comfortable making some observations.
Mine is a five inch system with the burn tunnel/base cast in perlite and cement. At the bottom of the feed tube is a grate. Below the grate is a removeable ash drawer. I can control the bottom air intake by how much this drawer is open.This whole base is wrapped in thin sheet metal for protection. The burn tube is 5 1/4" long and square. My riser is steel tubing filled with perlite. 33" high, 5"ID, 12 1/4"OD. The radiating barrel is 14" wide and gives 2 3/4" space above the riser. I have a duct comming of the bottom of this.
The first thing I will say is it is very easy to light. after placing my kindiling on the grate, I cover the feed tube and light it from below the grate. There is nowhere for the smoke to go but up the riser! Once the kindiling is going, I remove the feed cover and throw bigger chunks in to get a coal bed started. I have my bottom intake about 3/4" open. After about 20 min. when there are good coals, I close this down to about 1/4"-3/8".
The standard intake pulls air down the feed tube so only the tips burn. Most of the smoke and heat is at the bottom of the burn tube. It has been my observation that very top (1/2"-3/4") of the burn tube is pulling only air. By pulling some air (hot air) from the bottom, we are moving the heat up slightly. This is placing the burn higher up. I am burning more than just the tips of the wood and getting better mixing. I feel that I am preheating the wood a little more and can burn with higher moisture content. If I open the bottom air too much, or I get too much of a coal base, it starts to flame out the feed tube.
If the coals don't fall through the grate automatically, I just need to wiggle my sticks a little. I like that I can clean out the coals/ashes while its running.
I've still got a lot to learn, but I'm happy with what i've got so far.
I haven't brought it inside yet. I'm still trying to think of the best way to help heat my 2 1/2 story house with this. Running this by the wife is going to be difficult.
|
|
dave
New Member
Posts: 23 
|
Post by dave on Nov 17, 2009 9:07:50 GMT -8
What timing, I am planning on building a 5" rocket almost exactly how you describe yours.
Do you think it is big enough to heat your house? I wanted to build this as a sort of outdoor cook stove, with enough BTU to blanche tomatos, emergency water boiling, etc. Figure I could add a heat radiator later, if desired. Or use it as an outdoor boiler.
Any idea what yours weighs? I want to cast it in refractory cement. Planned on using lightweight furnace ducting for the tunnel and riser, and just let that thin stuff burn itself out after some test firings, leaving only the cement.
|
|
|
|
Post by canyon on Nov 17, 2009 10:33:41 GMT -8
Grizbach, thanks for sharing! Did you use straight portland cement and perlite? How is it holding up? What ratios? How thick is the walls and top of your burn tunnel? Thanks again!  |
|
|
|
Post by grizbach on Nov 17, 2009 19:54:58 GMT -8
Dave,
I designed it as a space heater, A stepping stone to a larger unit down the road. I won't know how it will heat untill I get it inside. My feeling is it will heat a large room, but not a whole house.
The weight is very manageable. About 65lbs for the base, 20lbs for the riser and 20lbs for the radiating barrel. It takes about 10 min. to put togeather.
Canyon,
I used masonary cement with the pearlite. I'm not sure of the ratio, I went for popcorn ball consistancy and then a little more cement. Maybe 4 to 1 perlite volume? The water I used I fortified with some local clay.
It's holding up great! I'm glad I have the metal outer casing (it acts like an egg shell) because you can scrape away at the concrete with you fingers. Luckily its designed so there is no abrasion at all. I only let it set a week before firing it. Waiting for the concrete to age is unbearable when you've got everything else ready to go!
The top of the burn tunnel is only an inch. I placed some hardware cloth in it while I was pouring it for strengh. As for the base, it is 1 1/2" at its thinnest. It gets very warm! If I were to do it over, I would make it 2" for added safety.
Thanks for the enthusiasim! I love to contribute if I can!
|
|
hpmer
Full Member
Posts: 240
|
Post by hpmer on May 31, 2010 16:36:27 GMT -8
I used masonary cement with the pearlite. I'm not sure of the ratio, I went for popcorn ball consistancy and then a little more cement. Maybe 4 to 1 perlite volume? The water I used I fortified with some local clay. It's holding up great! Grizbach, How many times have you now fired the stove, and is it still holding up well? I ask because I am thinking about building something similar but have heard that portland cement isn't supposed to hold up to the heat over time. I'm thinking about using straight portland rather than the masonary cement you used since I'm thinking it might be better to avoid the sand. |
|
|
|
Post by grizbach on Jun 1, 2010 7:37:43 GMT -8
hpmer,
I don't have a count of number of firings. Lets say about 13 times every two weeks, from Dec. to mid April?
The cement that is room temp, because of the pearlite, can be dented with a fingernail. Where it is exposed to direct flue gases, the cement breaks away easily. My cement is shielded from the direct contact of the wood with my stainless fire tube/grate.
Before the heating season this fall, I plan on examining the top of my burn tunnel. Probably need to do some patchwork to it. If I only need to do 1 hr. matainance to the cement once a year, I'll be a happy camper!
I read about someone building a forge, using sand in his refractory mix. Thats why I went with masonry. I coudn't tell you if it helps or hurts as this is my first attemp.
|
|
|
|
Post by Donkey on Jun 1, 2010 11:08:20 GMT -8
|
|
hpmer
Full Member
Posts: 240
|
Post by hpmer on Jun 1, 2010 13:54:01 GMT -8
Griz,
I'm more interested in whether it is cracking or deteriorating but I guess you solved that a different way.
I found some other site that suggested a 4:1 perlite/refractory cement mix that I am trying for the burn tunnel. Stuff's pretty expensive so I was trying for a less costly alternative for the rest of the stove. I suppose there's a reason for it though.
I like Donkey's home-made alternative, but am a bit short on ash reserves at present so was looking for a quick solution so I can be ready to go when it's maple sap boilin' time.
|
|
|
|
Post by grizbach on Jun 2, 2010 0:11:10 GMT -8
"I'm more interested in whether it is cracking or deteriorating but I guess you solved that a different way."
hpmer,
I haven't looked, but I believe the top of my burn tunnel is cracked. If I were to build it over again I would make it thicker than the 1 inch it is now. I don't think that this alone would solve the problem seeing that most systems have issues in this area.
Sounds like you have a good plan, keep the refractory mix in the burn tunnel and standard cement for the rest.
|
|
