Peter van den Berg

Orin Raichart wrote:Has  anyone put the p channel  under the  box instead of on top?  (seems to me the air intake would be inline with the flow of flame and gas instead of being forced downwards which disrupts the horizontal flow....yes, I know I would have to blow/clean the p channel out if it was placed on the bottom) ?

A p-channel on the bottom of the firebox is called a floor channel, its workings are different and it's a bit more complicated to make. As such it's similar to the secondary air channel developed by Matt Walker.

Orin Raichart wrote:In Option 1, how long does my 6" riser have to be?  Kirk Mobert's doesn't seem to be as tall as described by the spreadsheets or formula for these types of stoves.  The answer seems to be 43" for a 6".... can it be 32 to 36" and work correctly?

Donkey's cyclone batch rocket is a smaller system, it's a 5" system if I remember correctly. So the riser is shorter as compared to a 6" system.

I second Thomas, take down your J-tube and use the materials to create from scratch. Trying to adapt your existing heater will inevitably lead to cramped compromises.

John Goodbody wrote:Last of the 3 was so pronounced that sent the house vibrating before I maneged to grab phone and make this clip.

Sent the house vibrating? That isn't a slow pulse but a full-blown pulse jet sound, probably at 40 times a second! You doesn't say anything about fuel consumption while it is doing this but in my experience the combustion is accelerated greatly so the fuel is racing through. Below is an example of what my 4" development model was capable of 7 years ago. I'm still in the dark what is causing this, sorry.



Your RMH is acting as a valveless pulse jet, see Pulsejet by Wikipedia.

John Goodbody wrote:In another thread I also mentioned that during last two firings, the draw was breaking up, sounding almost like steam train, rather than rocket.
Does this hint anything to anyone?
Anyone had same issue?

A slow pulse, like a steam engine, 5 times a second or so points to a restriction somewhere in the system. The expanding gases would slow down, accelerate again, slow down, et cetera.
Most causes has been mentioned here I'd think, but I'll post those again, it might be helpful in some way.
Construction faults: Top gap between riser and barrel, manifold not enough space, too many bends, cramped transition to chimney, cold outside chimney.
Places where the hot gases need to change direction there should be more space. A 90º bend 150% of system csa, 180º bend 200%, so the space above the riser should be twice as spacious as the riser's csa suggests, in my own opinion. The same goes for manifold and bends further down the system. Sometimes there's a build mistake that causes a large  piece of cob fall down later on and block the system partially.
All these spots can act as a restriction although it doesn't look like that.

Restrictions that occur through time: ashes buildup in the tunnel/riser transition, on top of riser, in manifold, in elbows in a piped bench system. Straight single bell systems rarely clog up, floor area of most designs is large enough to house vast amounts of ashes. One of my designs showed signs of restriction down the line after ten years of use, cleaning the bell's floor fixed that issue.

Graham Chiu wrote:His temperatures aren't that high either; 400 deg C at the top of his riser when I believe Peter was getting 1300 deg C.

Not entirely true: 900º C (1650º F) at the top of the riser and very, very close to 1200º C (2190º F) 25 mm in front of the wall opposite the top end of the port. Difference is still huge, though.

Hi Linda,
1) It will take a skilled mason to build a brick bell which is gas tight. I would start with plastering the bricks in order to seal all the small leaks.
2) You say the chimney isn't above the roof line: at which level is it? Some people think a single-wall chimney pipe would do as the outside chimney, please believe me, it won't. Requirements for a good chimney: 3 feet above roof line, straight, smooth inside and insulated.
3) And yes, the vermiculite layer could still be wet since it tends to stock moisture in a very efficient way. A dozen firings won't remove that in my experience, keep firing that rocket ferociously.

Solving point 1 and 2 is absolutely necessary in my opinion.

Graham Chiu wrote:With 130 mm pipe I would have wrapped the blanket around the pipe and then burnt the steel pipe out over time.  I presume that's acceptable

Over time, the steel pipe  will deform badly, pinching the flow and disturbing the burn process until it finally collapses. Which means there's at least one burn season the heater won't work properly at all. Been there, done that, learned from it.

Ron Curtis wrote:I am thinking of refractory bricks for the feed and chamber and refractory tubes  4 x 33cm for the riser

Ron, those refractory tubes aren't suitable for use as a riser. They will crack, quite badly due to uneven heating. This could be alleviated to some degree by making one slit lengthwise. No guarantees it won't crack this way but they're stand a better chance to stay undamaged.

Those pipes are perfect for a mass bench though.

Thomas, you've experienced now what a virtually frictionless heat extractor can do. I bet the draw was present even before the ceramic core heated up!

Mart Hale wrote:
I want to make a mold for making rocket oven cores with air crete for Peter's  Van design.
I am curious where I can find more information about the molds made that have been tested.

Hi Mart,
All my casted experiments were done in a coated plywood or white melamine MDF box. All the sculpting was done with extruded polystyrene foam, made to size and shape with a table saw and smoothed by hand.

The foam parts were glued into place using double-sided adhesive tape, the kind that is used for fixing carpet edges to the floor. Any crack was sealed using acrylate sealant so no cement water leaked behind the foam parts. In fact, the pictured core is done like that.

Insulating the riser would allow reaching operation temperature sooner, but that's not all. Insulation has also the effect of getting higher temps so more volatiles will combust almost spontaniously.