Open System DSR2 Smoke-back

I have been experimenting with my 7" Sherman Tank DSR2 open system in the driveway until I feel confident enough to move it into the shop (luckily winter has been kind so far.)
I'm getting a lot of smoke back. Wondering if anyone can help me out/tell me what to look for as I troubleshoot. I know there's a few out there who are running this open front version of Peters design.  

Conditions: Full loads of dry wood that have gone great, smokeless, beautiful secondary combustion... but even those burns have sent some smoke back from the firebox as they settled down. I expected some smoke-back during the initial lighting. But I assumed that once the gasses started flowing through the system, they would keep moving through the flue due to the negative pressure drawing air in, not come out of the firebox too.

Was I wrong in this assumption? Should I just accept smoke-back in the open DSR2? Seems like I have too much to be acceptable.  

Here is a 26 second video showing what a small load of wood does. Being a small load of not great wood, it exaggerates the problem a bit. www.youtube.com/watch?v=l0l8ausB_uM  
Here is the original build post. https://permies.com/t/151576/Sherman-Tank-DSR-Rocket-Mass

One thing you can't see is how the 8" flue ends 8 inches from the floor of the tank. I have not yet added the columns of mass inside.

Thanks in advance!

Hi Matt;  
Were you really planning on running this rocket open face inside your shop?
Adding the columns inside the bell and getting them warm will certainly help.
Maybe as an experiment, hang some foil or sheet metal over the top 8" of your door and see if that helps keep the smoke inside.
The other thing is just how hot have you let this stove get?  With ceramic board and not much mass in your bell (yet) the smoke will always seek the path of least resistance.
An open door is much easier to find than the path thru your bell.
Add your columns. Get that stove hot, maybe add a foil deflector to encourage the smoke to go thru the system rather than around it.

I can tell you from my  batch stoves, that indeed they really get going with the door open... they are also over fueling heavily at the same time.
Do you know about "over fueling"?  A batchbox  phenomenon  very common directly after adding wood to a screaming hot pile of coals. You are not burning efficiently at all at that time. It stops a few moments later and settles back to a clean burn... With a regulated and directed fresh air supply.
The amount of heat coming out the open door is intense.   These batch  rockets of any design are not like the average box stove.
They get intensely hot fast. Having that heat go into your bell collects all that energy and saves it for later. Running an open door system your going to get vast amount of heat into your room quickly.
You will not be storing that heat in the bell.

Here is another idea.  If you have any  cfb left.  Craft a door that just slides in place and give it a 20% of the riser dia. opening for air.  

thomas rubino wrote: Were you really planning on running this rocket open face inside your shop?

Yes, but with a spark screen of course.  

thomas rubino wrote: The other thing is just how hot have you let this stove get?  

I've ran it full tilt, 550 degrees F on the top of the bell.

thomas rubino wrote: With ceramic board and not much mass in your bell (yet) the smoke will always seek the path of least resistance.
An open door is much easier to find than the path thru your bell.
Add your columns. Get that stove hot, maybe add a foil deflector to encourage the smoke to go thru the system rather than around it.

I'll sure try! I just assumed that once the smoke did find the path, which it did, that it would ALL follow the path instead of just some of it. Now I'm wondering if part of the problem has to do with she short test chimney and low mass. Factors that contribute to a lack of draw.

thomas rubino wrote: Do you know about "over fueling"?  

I'm familiar.  And I know this design is outside the main stream, but I figured if it worked for Peter it could work for me! Which is why I wanted to play around and troubleshoot a bit before conceding to adding a floor channel/secondary air tube/door (which I left room for in the design.)  

So I'll add the mass to keep the heat more even inside. Perhaps the lack of mass is why I saw smokeback at the end of a burn when the whole thing cooled down and gave the smoke less incentive to flow out the flue.
I'll play with a partial door, something that Peter did as well in the open design.
And part of me wants to increase the space between flue and floor... 8" is good on paper but maybe still too much of a 180 degree turn for the smoke to take. But I'll wait on that until I exhaust other options (I'll be damned if that ain't a pun!)
And if it all fails miserably then I know who to talk to about a proper door :)

Hi Matt;
I would say that a spark screen is a needed accessory!
Well 550 at the top  is good. And it drafted well then but as it cooled you got some smoke back.
Definitely add the columns and maybe some extra  chimney as well.
8" off the floor should be good.  Is the stack inside the bell insulated?  
If not, then before raising it try insulating it from the heat in the bell. You only want the cooler bottom air leaving via the chimney.
It is a very cool build! Keep playing with it.  You will figure out what works well.

The open DSR2 was operated with a spark screen instead of a door, yes. That particular screen would let air through over an area of about 60% of the total door opening's surface. That is quite different from totally open, I have to admit. In case you don't have a suitable screen at hand a strip of fireproof material covering half of the opening would suffice. That is, placed vertically in such a way there's an open space left and right of it, each occupying a quarter of the opening. In my case, that yielded the best results.
Hmmm... Hope this is clear.

Matt I commend your work, as you knew before you started there would be some experimentation, and I find myself doing much of the same work as you. trying to follow the guide lines as much as possible, (why reinvent the proverbial wheel)  

I have asked this question before on another forum your well versed on,  and that is just how close to the bell side can you get with the top flue opening of your DSR2?, to which I never got an answer. (I probably didn't ask in the right spot or manner) But knowing how the formula works, and looking at your photo of your barrel with the DSR2 sticking out, I have to ask "how close is yours" Please be assured I don't know if this has any factor.

Also, you wrote  One thing you can't see is how the 8" flue ends 8 inches from the floor of the tank. I have not yet added the columns of mass inside.

What does this mean? Did you mean the inside flue (inside your bell) goes up to within 8" of the TOP of the bell? Or something else?  Perhaps I missed this on your build photos.  And lastly, I presume you built this out of the ceramic board as well?

The Closing up the allowable door space answers may change many things for the better for you, hope so.

Keep up the good "testing" work.

Peter van den Berg wrote:The open DSR2 was operated with a spark screen instead of a door, yes. That particular screen would let air through over an area of about 60% of the total door opening's surface. That is quite different from totally open, I have to admit. In case you don't have a suitable screen at hand a strip of fireproof material covering half of the opening would suffice. That is, placed vertically in such a way there's an open space left and right of it, each occupying a quarter of the opening. In my case, that yielded the best results.
Hmmm... Hope this is clear.

Very clear Peter, thank you. I must have misunderstood the development thread on Donkeys board. It looks like you started fully open with just a spark screen but eventually found the "partial door" to yield the best results with openings on each side. I will cobble something together like you did and give it a try!

Matt,  If that is your idea of a "cobbled door", then I'd probably just drool over what you would consider to be a proper door!  Great job!

If you have any construction photos of it, I'd love to see them.  Thanks.

Gerry Parent wrote:Matt,  If that is your idea of a "cobbled door", then I'd probably just drool over what you would consider to be a proper door!  Great job!

If you have any construction photos of it, I'd love to see them.  Thanks.

I WISH! That's actually Peters door from his DSR2 development thread. I included it to kinda confirm/demonstrate what he meant by his text description. My own metalwork is a long way off from that level!

Scott Weinberg wrote:I have asked this question before on another forum your well versed on,  and that is just how close to the bell side can you get with the top flue opening of your DSR2?

My own experimental setup had the top front exhaust of the DSR2 about half an inch from the barrel's inside. I expected the barrel to be much hotter than the rest but it didn't turn out that way.

Matt Todd wrote:

Gerry Parent wrote:Matt,  If that is your idea of a "cobbled door", then I'd probably just drool over what you would consider to be a proper door!  Great job!
If you have any construction photos of it, I'd love to see them.  Thanks.

I WISH! That's actually Peters door from his DSR2 development thread. I included it to kinda confirm/demonstrate what he meant by his text description. My own metalwork is a long way off from that level!

Thanks for the compliment Gerry, metalwork isn't one of my strong points, I actually dislike it but sometimes can't avoid. My wife complains now and then that I tend to become quite grumpy when I have done grinding and welding.

Peter van den Berg wrote:

Scott Weinberg wrote:I have asked this question before on another forum your well versed on,  and that is just how close to the bell side can you get with the top flue opening of your DSR2?

My own experimental setup had the top front exhaust of the DSR2 about half an inch from the barrel's inside. I expected the barrel to be much hotter than the rest but it didn't turn out that way.

excellent Peter, I should be in good shape then..

Cheers
Scott

Scott Weinberg wrote:
I have asked this question before on another forum your well versed on,  and that is just how close to the bell side can you get with the top flue opening of your DSR2?

My top core opening is something like 2.5 inches inside from the front wall. I could have stuck the core further in, but I wanted to leave plenty of room for air flow around the flue pipe behind it.

Scott Weinberg wrote: Did you mean the inside flue (inside your bell) goes up to within 8" of the TOP of the bell? Or something else?  Perhaps I missed this on your build photos.  And lastly, I presume you built this out of the ceramic board as well?

Think of this tank as a cup and straw. The tank is the cup, the black stove flue pipe is the straw. The pipe is bolted to the back wall of the tank so that it can end 8 inches from the bottom, leaving room for the exhaust gas to get sucked up and out from the bottom. I have two 24" pieces of stove pipe bolted in there, which left about 10" sticking out of the top that I can attach more stove pipe to for my chimney. This little diagram I drew probably explains it better.

Looking forward to seeing your own design! I know mine sure took longer than expected to bring into the world, with lots of work left to go.

Scott Weinberg wrote: Did you mean the inside flue (inside your bell) goes up to within 8" of the TOP of the bell? Or something else?  Perhaps I missed this on your build photos.  And lastly, I presume you built this out of the ceramic board as well?

Think of this tank as a cup and straw. The tank is the cup, the black stove flue pipe is the straw. The pipe is bolted to the back wall of the tank so that it can end 8 inches from the bottom, leaving room for the exhaust gas to get sucked up and out from the bottom. I have two 24" pieces of stove pipe bolted in there, which left about 10" sticking out of the top that I can attach more stove pipe to for my chimney. This little diagram I drew probably explains it better.

Looking forward to seeing your own design! I know mine sure took longer than expected to bring into the world, with lots of work left to go.


Thanks Matt, I could not for the life of me, envision this, but your drawing makes perfect sense to me now what your doing, I had just  never thought of the flue on the inside of the bell,  I was/am doing on outside at the bottom, which of course makes doing the bypass a bit harder, but it will work out.

I love and do metal work for a living so am looking forward to some of the door things    Just might have to do a adjustable, in/out, bigger/smaller experimentation door. But will certainly start with Peters "best calculation" as the first try.   As for the rest, I am sticking as close as I can, the 57 ISA, this was my largest calculation to get just right... think we got it now.  my mass, will start out with 4.75" of granite, all sides, because I have it. I can add more, would be tough to take away.  Time will tell!

I have my other stove up and running for the winter, so this one I hope to have done by spring.. and hope to test by end of March.  to much work to NOT do it right.

cheers, Scott

Scott Weinberg wrote:
Thanks Matt, I could not for the life of me, envision this, but your drawing makes perfect sense to me now what your doing, I had just  never thought of the flue on the inside of the bell,  I was/am doing on outside at the bottom, which of course makes doing the bypass a bit harder, but it will work out.

I did it this way precisely because I'm not great at metal work, and making a round hole was much easier on the flat top of the drum than the curved side. Plus it meant one hole instead of an additional hole for a bypass.  And it will help me with my wall clearance once it moves inside. One thing the nice folks here at Permies have pointed out to me is that you can have a bigger bell than the ISA calculation as long as you have a bypass to get the flue warm and drawing. Best of luck to you and your build!  

Here's my very crude door. Just CFB scraps sprayed down with sodium silicate. It hangs on two metal brackets and blocks around 60% of the firebox opening.
One burn with the "door" so far. It was a much more consistent and even burn than before so I think I'm moving in the right direction with the tinkering.

One thing that really stood out was how the fire didn't stay back at the port end. Once the burn got going, it traveled down the wood toward the front of the box until all of the wood was burning at once (instead of the typical back-to-front burn.)
Is that normal in a batch box? Does it mean anything in particular to anyone?

Hi Matt;  Looking good!    
Yes, it is normal in a closed batchbox for the entire pile of logs to be burning at the same time.
So I would guess that a properly vented open batch would do the same.

Everything you document is helping a fledgling rocket scientist gain the courage and confidence to attempt their first build!
Keep up the good experimenting!  And keep the posts (with pictures) coming!