Terry Sommers

here's a diagram of my basic set up. My main questions relate to the j rocket design. the external size of the riser is 49 cm, the internal dimension of the riser, with the 5.5cm of insulative refractory cement/perlite is about 44.5 cm. so, using the ratios i've come across, the burn tube which is horizontal with the ground is around 22 cm long. Now, my big question is where should i locate my secondary burn? I'm thinking right near where it enters the riser, maybe 1/3 up the riser, i'm not sure. but it will be off-center so that it helps to spin the gasses and create a vortex. I'm thinking of putting in 2 secondary air inputs, with valves at the beginning of the tubes so i can precisely control the amount of air that is allowed in, or letting me cut it off completely. also, with an internal riser cross section diameter of 11 cm, should i have small copper tubes for the air intake (which would allow for heat tolerant valve controls), or do i need bigger diameter pipes for that?
and about halfway up the riser, will be the input for the saw dust feed. I already have a low speed motor to turn an auger to feed the sawdust into the rocket, and if i choose i can block off that entry. I can also adjust the speed of the saw dust feed motor, but only by about 50%. I can get the motor to turn as slow as 20rpm. So, what do you guys think of this? Oh yeah, and i have some questions on the burn section, the horizontal part. Should i make a venturi tube, then expand it gently before the riser, or just keep it straight? I'm casting this in 2 pieces, use a bunch of sand, cover with crappy vent tubing, then plaster over that so i can later add contours to the burn tube, riser, such as the venturi section, ash scoops, slight wings in the risers to help the vortex spin.

Miles Flansburg wrote:Howdy Terry, welcome to permies!
Here is my favorite video of a rocket pizza oven design. Maybe it will help?

https://www.youtube.com/watch?v=5OIZekftbxw

https://www.youtube.com/watch?v=UId4mT4NcJw

Also do you have any pictures of yours?

thank you, i've watched those two vids a couple of times, somewhat the same approach, though my thermal mass is probably 1/3 or 1/2 of that, going more for insulation with only 1 inch of hard heat storing mass, the other 3 inches are insulative concrete. I reckon that with a good rocket, the thermal mass doesn't need to be too high, particularly with good insulation.

thank you all for your suggestions. My problem is that the oven comes in basically 3 parts: the rocket, the bottom half of the cook space (which seats the cook floor and has the entrance for the rocket shooting directly under that, looks vaguely like a sink) and the dome/door/exhaust part. Since the chimney is housed internally in the dome, it would be impossible to make the hole bigger. I thought about adding a bigger rocket, and making the hole in the bottom half of the oven bigger, but it seems that there would end up being a bottleneck in the dome for the extra exhaust gasses.... or maybe that would be a good thing???. So, what i've decided to do is build a j tube rocket with a refractory cement perlite mix, cast in 2 halves, with ash pit and cleanout area, and in the riser, have a preheated input of clean air, just below the sawdust feed. I have a slow speed motor that will turn an auger (exaggerated screw) that will slowly press sawdust into the rocket riser at a 90 degree angle, and the idea is that the fresh air will help the combustion and diffuse the sawdust for a cleaner burn. I think in this way i can increase the temp of the cook chamber to pizza temp. I'll include the drawings and photos later, probably tonight. dthanks again! and i'll be checking in every day or so with progress reports

I made a rocket powered pizza oven and tried it out for the first time yesterday, and though it makes a great oven, it is not yet a pizza oven, as the temperature is about 150 degrees f too cool. I need at least 600 degrees, 700 is ideal, but the dome temperature was only 450 at the most, and the floor was only 550 at the most. The door is made to accommodate pizzas, basically 8 inch height, so a loaf of bread isn't going to come back out. Besides, i am a pizza business, not a bread business. I figure that the problem can be fixed by creating a better rocket, as the one i am using now most likely isn't very efficient. I'm quite sure that my oven cooking space is very efficient, but i just need more raw energy to heat up that insulated mass. It's cool enough after 3 hours that i can touch the sides of the cooking space, while inside it is 400 degrees. So, my plan is to cast an insulated refractory j tube. The j tube is mainly to reduce the work of feeding the fire, letting gravity do the work for me and freeing me up to deal with customers and making pizzas. I will use perlite in the calcium aluminate cement with a bit of sand. also, i will insert a copper tube with a valve at the intake for the purpose of delivering oxygen further along the burn tube, and i can regulate the oxygen flow with the valve. The copper tube will run along the burn tube to heat up the air, ideally coiling around it. also, i will create a vortex in the riser, as i have read that this increases efficiency. Then entry to the oven is a 10cm square, capped by a diffuser, which is topped by the cook floor. The hot gas is forced to the back of the oven, then rises along the dome, then before the door, is forced up an internal chimney which takes the hot gas back over the dome, but the other side of it, and finally to the chimney and out of the oven. the chimney and dome are also well insulated, and can be further insulated with a ceramic fiber blanket. However, i know that since the cook floor isn't even 600 degrees, despite its proximity to the rocket gasses, the blanket will still not bring me any closer to a rocket powered pizza oven. The internal dimensions of the cook space is roughly 40cm by 40cm, following the .62 ratio of door/dome height. Again, what i need to make this thing work is a more badass rocket. I know i could make another rocket and have the two of them going side by side, but that will take more retro work on the pizza oven part. So, I WANT TO FIGURE OUT HOW TO MAKE A BETTER, ROCKING ROCKET. any Einsteins of the rocket world here to lend a mental hand? Thanks!