Rocket mass heater, first build + burning problem

Hello , this is my first post on here.
I m from Romania, far away, and I am trying to build my first rocket mass heater with a stratification chamber.
I have attached some photos with the build. It s a 8" system(20cm diameter) and I think the riser is not drawing enough. I haven't set the chimney in place , just put it out the window for a fire test.
Some dimensions are as follows: the riser has 1m in height and 19.5 cm diameter(aprox 8"). The horizontal fire chamber has an area of 18*15cm and length of approx 25cm.

What could be the issue? Or is there an issue? Maybe after the chimney installation all will be fine? As you can see from the pictures with the fire test, sometimes it burns vertical and not horizontal.
Thank you!

Hi Nahara;
Well, the first thing is, All new build RMHs have draft issues while all the moisture dries out.
If you are lucky that could be your only problem.

Things that I have noticed,  your transition area below the barrel appears to be much too small, it needs to be large.
It would defiantly help if you had a bigger opening to convince your exhaust to flow into your stratification chamber.
How large is your "chimney" opening leaving from your Strat chamber?  It must also be quite large to keep the flow of cooling air moving out of your chamber and up your chimney.
And last, you are currently "testing" by sticking the uninsulated pipe out the window, you lose heat there.
Wrap an insulator around that pipe, you want the air in your chimney to stay warm enough to draft.

Your build looks great and once you get it dried out and heated up you will be happy!

thomas rubino wrote:Hi Nahara;
Well, the first thing is, All new build RMHs have draft issues while all the moisture dries out.
If you are lucky that could be your only problem.

Things that I have noticed,  your transition area below the barrel appears to be much too small, it needs to be large.
It would defiantly help if you had a bigger opening to convince your exhaust to flow into your stratification chamber.
How large is your "chimney" opening leaving from your Strat chamber?  It must also be quite large to keep the flow of cooling air moving out of your chamber and up your chimney.
And last, you are currently "testing" by sticking the uninsulated pipe out the window, you lose heat there.
Wrap an insulator around that pipe, you want the air in your chimney to stay warm enough to draft.

Your build looks great and once you get it dried out and heated up you will be happy!

Thank you for the fast reply, Thomas! Also for the encouragement:D i really appreciate it!

The transition area from under the barrel had a support brick that i removed later on the build so the are is now roughly 24cm vertical x 10-11 cm horizontal. (A bigger area then the riser has).
The flexible aluminum chimney (not the best choice but definitely the cheapest) has 20cm diameter (8") so it is slightly bigger or the same as the riser.
I was thinking of having the chimney vertical near, or close to,  the barrel to help with the cold gasses/cold plugs...

Ok, your transition area sounds large enough.  
Your outlet from the strat chamber could use a larger entrance (think funnel), say 10" down to the 8" chimney pipe.
Having your chimney pass near the barrel always helps.
However once dried out and warmed up that may not be necessary.
A handheld propane torch can be used if needed to heat your outlet chimney, to help start the flow of gasses.

Nahara;
What material is your riser made from?  
They look similar to clay chimney liners.
The clay chimney liners are well-known to crack from the rapidly changing temperatures (thermal shock)  produced inside a riser.

thomas rubino wrote:Nahara;
What material is your riser made from?  
They look similar to clay chimney liners.
The clay chimney liners are well-known to crack from the rapidly changing temperatures (thermal shock)  produced inside a riser.

They are firebrick tubes, got them because they are round and I thought that will increase the draft/pull by reducing turbulences

There's one more possible restriction point, the top gap between riser and top of barrel. The recommended distance of 5 cm is the absolute minimum. Anything less and the thing will be very stubborn to work as intended. In order to round the 180 degrees turn in direction this should be at least 15 cm in order to avoid a pinch point.

Your transition opening is the wrong way around, 10 cm high and 24 cm wide would already be better, sorry to contradict you, Thomas. Imagine all the gases are coming down and are trying to pass your 11 cm wide opening. Some of it will take the top end, more volume need to go further down, creating a turbulent pinch point.
And even with the opening turned 90 degrees, it isn't wide enough. Your riser is about 20 cm diameter, its cross section area is 314 m² then. Your opening is smaller than that, 216 cm² so it's obviously far too small. The correct opening should be at least 150% of the riser's CSA, certainly not equal or less. Please have a look at this thread at Donkey's about this phenomenon.
https://donkey32.proboards.com/thread/337/helpful-hint

In order to have enough draft going through the system, the chimney should reach at least 2 meters above the barrel. Straight out of the window will throw the potential of the thing ...ehrrmm... straight out of the window. A horizontal exhaust is something like an urban myth: it won't work unless it's at the lee side of the house, with no other openings higher than the exhaust. Even a drafty roof or door will provide more suction than the exhaust itself. This won't work, forget about it.

Thank You Peter for the mathematical correction!
After my post, I did the math and realized my mistake.
I was writing a new post to correct that when your post arrived.

Nahara,  Firebrick tubes you say?  
Hmm,   Those have the potential to be very very good risers!
Do you know the temperature rating on them?
How easy were they to get and what was the cost?

Peter van den Berg wrote:There's one more possible restriction point, the top gap between riser and top of barrel. The recommended distance of 5 cm is the absolute minimum. Anything less and the thing will be very stubborn to work as intended. In order to round the 180 degrees turn in direction this should be at least 15 cm in order to avoid a pinch point.

Your transition opening is the wrong way around, 10 cm high and 24 cm wide would already be better, sorry to contradict you, Thomas. Imagine all the gases are coming down and are trying to pass your 11 cm wide opening. Some of it will take the top end, more volume need to go further down, creating a turbulent pinch point.
And even with the opening turned 90 degrees, it isn't wide enough. Your riser is about 20 cm diameter, its cross section area is 314 m² then. Your opening is smaller than that, 216 cm² so it's obviously far too small. The correct opening should be at least 150% of the riser's CSA, certainly not equal or less. Please have a look at this thread at Donkey's about this phenomenon.
https://donkey32.proboards.com/thread/337/helpful-hint

In order to have enough draft going through the system, the chimney should reach at least 2 meters above the barrel. Straight out of the window will throw the potential of the thing ...ehrrmm... straight out of the window. A horizontal exhaust is something like an urban myth: it won't work unless it's at the lee side of the house, with no other openings higher than the exhaust. Even a drafty roof or door will provide more suction than the exhaust itself. This won't work, forget about it.

Thank you, Peter, for your reply!
1. I have 6 cm between barrel and top of riser, so I guess I m good there
2. I will modify the transition to have an area bigger than the area of riser and oriented properly.
3. If I cannot lift my chimney that high, what other solutions do I have? I cannot pass through the ceiling, unfortunately. I can lift the chimney, 2 m over the barrel, outside the building. Will that do the trick?

thomas rubino wrote:Thank You Peter for the mathematical correction!
After my post, I did the math and realized my mistake.
I was writing a new post to correct that when your post arrived.

Nahara,  Firebrick tubes you say?  
Hmm,   Those have the potential to be very very good risers!
Do you know the temperature rating on them?
How easy were they to get and what was the cost?

Thomas, I think they are rated at 600 degrees Celsius. Though, i hope they can withstand higher temperatures...
I purchased them from a local shop, in your currency i think they were 13-14$ a piece. Not a bargain for me and my place of origin (they seemed rather expensive) but I had little experience in building so I went for most standard materials that i could afford.

Nahara Radu wrote:1. I have 6 cm between barrel and top of riser, so I guess I m good there

I won't agree, when the barrel heats up and the lid start to get hollow, you'll have a problem. My recommendation would be 15 cm, at least.

Nahara Radu wrote:2. I will modify the transition to have an area bigger than the area of riser and oriented properly.

That would be the proper action.

Nahara Radu wrote:3. If I cannot lift my chimney that high, what other solutions do I have? I cannot pass through the ceiling, unfortunately. I can lift the chimney, 2 m over the barrel, outside the building. Will that do the trick?

Not quite, sorry. In order to work in all circumstances like being at the windward side of the house the chimney should reach at least 50 cm above the highest point of the roof. And... all of the chimney outside should be properly insulated. And even then, when frosty outside and a cold heater you might experience the "cold plug in the chimney" phenomenon at the moment you are trying to light it.

Ahh, if only they were rated for 1200C then they would make batch box risers.
At 600C they are rather low but may work ok on a J-Tube for you.

Creating a cast at-home riser of fireclay and perlite is not difficult.
If the tubes do not hold up, this could be a low-cost alternative.

Regarding the ceramic tubes, I have seen commendable results by making one vertical slit in each of those. The problem with tubes of any kind isn't the temperature perse, but the unequal heating up of those. Cracks will develop quite quickly, although the pieces tend to stay in place. Cutting the tube vertically will act as a pre-crack.

Even with the DSR3's horizontal afterburner tube I could use a 600ºC item divided in three pieces and rendering it bright cherry red everytime without breaking up any further.

I can see a few potential problems not least every thing looks very damp if not wet, the chimney is not good and i wonder about the amount of ceramic fibre around the riser, how much gap is there around the riser to the barrel?

The stove will never work very well while the bricks are damp but in order to dry them you need to get the stove running, i think you need to first address the chimney situation.

Nahadu, I sincerely hope you will be able to solve the chimney problem. I forgot to mention that the opening between the barrel and bell would be best much, much larger. As I found out, this opening could be as large as all of the width and height of the brick bell. In other words: completely open to each other.

All the internal space of the barrel and bell would act as one larger bell. In your build, the brick footing of the barrel and the brick bell would be just one construction. In this case, the placing of where the exhaust would be situated is largely unimportant, anywhere around the perimeter is possible.

This configuration was used in the Mallorca build and the Bell with two benches as well.