J * tube to Batch Box Conversion

This is all becoming a lot more clear. Thank you both.
Now, if I can reiterate what was said for clarity.

The port for a 6" batch box from Peters chart is 2.19" x 9.5" = 20.81 sq in (52.86 sq cm)

So 5% of 20.81 (52.86) =  1.04 sq in  (2.64 sq cm)

Total hole or slot size on top of riser then needs to be:  20.81 + 2.64 = 23.45 sq cm

With this second port added to the riser, its now sounding a lot like Matt Walkers riserless core design which also has 2 ports with an expansion space inbetween them (just laid down level)

Think I might try a circle first made with cf blanket.
Cf board would be a better choice but I don't have any on hand.
Also, with the wrinkled nature of the cf blanket at the top of the riser, doesn't make it a real accurate science but I guess close enough will have to do.




     

Gerry Parent wrote:This is all becoming a lot more clear. Thank you both.
Now, if I can reiterate what was said for clarity.

The port for a 6" batch box from Peters chart is 2.19" x 9.5" = 20.81 sq in (52.86 sq cm) Nope, 20.81 x 6.5416 = 134.257796 cm².

So 5% of 20.81 (52.86) =  1.04 sq in  (2.64 sq cm) Nope again,  134.257796 X 1.05 = 140.97 cm²

Total hole or slot size on top of riser then needs to be:  20.81 + 2.64 = 23.45 sq cm

With this second port added to the riser, its now sounding a lot like Matt Walkers riserless core design which also has 2 ports with an expansion space inbetween them (just laid down level)

Think I might try a circle first made with cf blanket.
Cf board would be a better choice but I don't have any on hand.
Also, with the wrinkled nature of the cf blanket at the top of the riser, doesn't make it a real accurate science but I guess close enough will have to do.




     

You forgot to square your centimeters!

Well, after a request, i have to explain innit!

And inch is 2.54cm.  And a square inch is 2.54cm x 2.54cm, hence 6.5416.  Does that sound sensible? ;D

For conversion of imperial to metrics and vise versa I am using Cleave Books Specialist Calculators. About any conversion is in there, money excluded. Satamax is right, but you are gonna use imperial I'd think.

Peter van den Berg wrote:For conversion of imperial to metrics and vise versa I am using Cleave Books Specialist Calculators. About any conversion is in there, money excluded. Satamax is right, but you are gonna use imperial I'd think.

Having learned guitarmaking at school in uk, and in the book of Cumpiano and Nathelson. Where it's all in inches. I am used to do the conversions with a calculator. Pretty easy once you have the basic numbers in your head.

Imperial decimal, and imperial fractional! Why guys, why?

Today I had some time to experiment with Peters idea to restrict the end of the heat riser.
This first test was done on my 6" diameter heat riser with a ring made from 1" thick cf blanket to 5" diameter restriction.
I had calculated a 5% larger surface area than the port to be 5 1/4". I just kept it simple and made it 5" instead.
Not really sure if I'm looking at containing more of the flame than without the restriction, but take a look a the photos and short video and tell me what you think?
It did seem that the flame was more concentrated than it was during the first run however, I went through a batch with a single barrel on to eliminate all the startup smoke from getting into the shop this time. Perhaps that was the difference in flame appearance.
The draft appeared not to be any different to me than without the restriction doughnut so it could be reduced and tested again if needed.

Step one..prepare the heat riser for insertion of the doughnut.



Doughnut installed and ready to go.
5" diameter opening



Calgary Flames mascot



Approx. 2' flames out of riser

Gerry, in my DSR setup the distance from the riser port to the end port seems to be crucial. I recalculated your numbers and those seem to be correct. You could leave it like it is now, place the second barrel on and see how it goes.

OR you could try other doughnut diameter holes to see if it would make any difference. The length of the riser ought to be a factor also, and last but not least: I honestly don't know whether this trick will work on a vertical riser, ever.

Great experiment Gerry;
Your braver than me lighting off indoors like that.
Your flame seemed just as strong but only time and controlled testing will tell you if it is an improvement.
Maybe Dragon Tech should invest in a testo...

Peter van den Berg wrote:Gerry, in my DSR setup the distance from the riser port to the end port seems to be crucial.

If this distance is crucial, then would a shorter or longer riser be worth experimenting with? or would the riser need to stay at minimum stock 43 3/16" length?
I know this is experimental for even you but if you had to guess.

Peter van den Berg wrote:OR you could try other doughnut diameter holes to see if it would make any difference. The length of the riser ought to be a factor also, and last but not least: I honestly don't know whether this trick will work on a vertical riser, ever.

Its a simple enough experiment to try a few more different configurations so I think next time, I'll reduce it to about a 4" diameter which by then should really be noticeable, then back it off until it seems right. This is a real hillbilly type experiment with no gas analyser but at least satisfies a curiosity.

Thomas, Always have a fire extinguisher on hand along with the barrel I can quickly cap it if needed. Certainly not something that can be walked away from though! This dragon has its muzzle removed so look out!

It could either the shorter riser or the smaller diameter throat, or both. My guess would be start with the smaller throat, that's more or less how I did it.

Important: if and when it's too small the heater becomes very sluggish and no flame at all comes out of the riser. A little bit larger throat might make the difference. In my view, there's a trade-off between slugginess and overfuelling, a little bit held down is enough to prevent thermal runaway in 90% of cases.

So with this next experiment, I made the restriction 4" at the top doughnut. With the barrel on, I lit a fire and let it get going good for about 10 minutes. Draft again was not affected by the increased restriction.
I then removed the barrel and found that it was burning clean with no smoke coming out the riser. With a mirror I could see the double rams horns at the base and with NO flames coming up OR out the top of the riser. I started to close the combined air inlet about half way and quickly it started to smoke. The more I closed it, the more it smoked. Opening it fully made it burn clean again.

Also, I wanted to see what would happen if I reduced the restriction even further on the fly. I placed a small strip of cf blanket across the top of the riser and just like what happened when I started to close the combined air inlet it started to smoke. Removed the piece and it was fine again.

During this test, the firebox was only about half full so I put more wood in leaving about 2" from the top. Air inlet was left fully open. A few minutes later, flames started to peek out of the riser, and with a bit of smoke. The higher the flames got, the more smoke that seemed to come out and quickly filled the shop. Cough, cough..... Quickly capped it with the barrel and got out of there as the smoke was very stinky.

So it appears that as long as there is not too much fuel in the firebox, it burns clean. Too much fuel and it over fuels with a dirty burn. Any flames that come out the riser are not a good thing for a clean burn.
The pieces of wood in the firebox were not overly small either in diameter (approx. 3"x3").
Restricting the air inlet is not an option nor is going much below 4" diameter any helpful either.
Do you think the circular shape is not ideal and needs to be a slot instead?
I don't know what would happen if I shortened the riser length but don't really want to cut my riser in half if at all possible unless there is a high chance it will help eliminate over fuelling.

Gerry, you're overfuelling.

In your first video, with the flames shooting out, i can see the firebox crammed with bits of wood. I can see the pulsating, which to me means you don't have enough primary air. I'm quite high above sea level; and i had to increase the primary air. And i can tell you, i know your problem!



The solution has been to cut proper firewood.



I use larch now that i have my combine splitter machine, which might give me trouble again; But with oak that big and even a bit smaller, it was fine.

If you use softwood offcuts to light the stove, don't fill more than a third of the firebox, half absolute maximum. When they are at half ember stage, add bigger wood. If you want to burn those to get rid of waste, mix these with bigger wood. In my firebox, which is 33cm wide iirc, x 50cm high. I put 6 to 8 pieces of wood, about 10cm shorter than the firebox itself. Always leave a space at either end for the air to spread, and for the flames to develop. Always leave space above the wood. Don't burn too much fatwood.

I admit, i have an advantage to monitor my fire, with the window above the heat riser.


Hth.

Gerry, a slot might or might not be better, I simply don't know. As I said, nobody tried this on a bog standard batchrocket before plus there's always the possibility that it won't work at all. Assuming it could work though, it's a sliding scale antway between too sluggy and overfuelling. The difficult point here is to find the sweet spot where both effects are in a reasonable balance.

I agree Satamax and Peter with your comments. Achieving a balance is a delicate matter when it comes to burning clean with this type of setup.
At this point I am satisfied with my results with the doughnut experiments and will now just experiment more with wood size and volume as Satamax suggested.