"Rocket-Grill" AKA rocket stove bbq

[fredwalter]

Here is something interesting, a rocket stove bbq with lots of instructions:

www.instructables.com/id/Rocket-Grill
and
ecorenovator.org/forum/biofuels/1052-building-rocket-stove.html

He used 6.5" diameter steel pipe for the feed tube and burn tube, and didn't insulate it.

Anyone know enough to say what would happen if someone used 4" diameter steel tube (well casing)?

I'm assuming if the burn tube was insulated, that the bbq would be more efficient, but would the cooking temperature go up (perhaps too much)?

[hpmer]

4" vs 6.5" will work fine, though the larger diameter will have a substantially better heat output. I've built stoves with both dimensions and the 4 incher is harder to burn clean (mine were both insulated with 2" of insulation).

My latest version is a portable stove that I use in much the same way he does, though mine is a more traditional rocket stove ("J" type design with insulatation all the way thru). I like to cook with temps about 600 degrees f measured at the top of the heat riser. At that temp the flame nicely "streams" off the wood. My thermometer only goes to 1000 degrees f, so I don't know how much higher it will go, but I regulate the heat by how much fuel is burning at the time.

[madidaddy]

My 4" stainless T did a great job BBQin this weekend.

[panbreaux]

my 4" rocket tends to pile up coals and ashes. i haven't tried insulating it yet. i think my stack is a bit too long for it to eject the ashes efficiently. in the video it has about 10' of stove pipe on top of the 3' riser. running it with just the 3' riser makes it pile up worse. if it was covered with a drum for a mass heater, with the 10' chimney it would probably work ok. when i took the legs off and added a vertical feed the heat built up in the feed tube. when it's run as in the video with the fire in the tube the heat builds up in the elbow and riser bottom. if you made a smaller version than mine similar in proportion to madidaddy's it should work great as a stove. with the fire box on the end and a stack of cinder blocks around the stack i tried boiling a few cups of water in a kettle and was only able to get the temp to 180* using pecan wood. i haven't tried to boil water feeding it directly into the feed tube yet. i'm thinking of leaving the feed tube as is and adding in a vertical feed as close as possible to the elbow that would allow me to cover it with a lid for a mass heater. i just need to make it long enough to enclose the wood and be able to cap it so the air moves across from the end. i'm hoping to set it up so that it sucks it's air from outside to decrease the vacuum on the house that can suck in cold air through any leaks and make it less temperamental with wood size and placement. a video of it running as a suction fed forge> www.youtube.com/watch?v=VakZS-kxXUo&list=UUo5QBn5owO8X6ygfRDQVe6g&index=9&feature=plcp

[madidaddy]

I didn't see a shelf for the wood, which seems to help with a cleaner burn. This would allow combustion air to pre-heat, and keep the wood out of the coals. The problem I had with elbows is the burn time is less due to ash going into where pre-heated air should feed. The T seems to work better.

[peterberg]

Feb 3, 2012 5:10:58 GMT -8 panbreaux said:

my 4" rocket tends to pile up coals and ashes. i haven't tried insulating it yet.

One of the rules: insulation! By omitting that, your stove will burn but won't work like a rocket. And please, do add a shelf, leaving that out is another part of the problem.

[leewaytoo]

is the "rocket sound" a result of "sonic wave"?

[woodburner]

If the sound in the video in panbreaux' post is the rocket stove sound, then it sounds to me like a typical standing wave set up in the pipe. Its frequency will vary depending on the length of the pipe. So yes, could be termed a sonic wave.