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!!!!! J tube to Batch Box Conversion

 
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Gerry Parent wrote:In regards to your comments to Thomas, all I can say is that I would never want to have my open minded tinkering nature stifled by others opinions.
I would like to say a lot more but probably would end up being a 'cider press' conversation at that point so.... long story short, you have been nothing but an inspiration to myself and I'm sure many others out there and would dread the idea that you were holding yourself back because of some limiting ideas..... therefore, you have my vote on helping you to keep your imagination tickled for as long as possible! GO Peter GO!


Thanks Gerry, you are surely know how to drive away a person's gloomy worries.

There might emerge some (hopefully simple) addition to the old and trusted J-tube in future. But don't hold your breath, I am working on several projects at the moment. All about building and workshops and so on, no firm plans for experiments as yet.
 
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Nobody should have any expectations from you Peter, er.... except maybe your wife ;) ...groan.... but I do know the way that little girl is wondering and imagining possibilites, that's the way it happens.
In time, I look forward to any tidbits you are ready to share.
In the meantime, with all the snow we've been getting here, I've been plowing on the tractor almost non-stop. I did however take an hour break yesterday and implemented the single air opening as you suggested. Its situated very low and looks right into the opening of the floor channel. see picture below. Using a sawzall with a metal blade made quick work of opening it up. I didn't have time to make an air controller yet but as you mentioned, all open or all closed is the way I'm going with for now.
Dimensions are: 4.25" x 1.5" =  6.38" csa  So, a little smaller than yours (at 6.92 csa) but its just formed out of cob so it can easily be added to or removed from if needed.

Some of my initial observations:
With the new air slot, I wanted to see what affects it will have on the pulsing, so I removed the threshold before starting the fire. I lit a small fire at the base of floor channel stub, then made a little bridge with two sticks (one at the front and the other near the back) to hold up the wood a little bit so that there was an air channel all the way to the back. When I put the door back on, the small fire picked up considerably. With it off, it was mediocre. I loaded the rest of the wood in and again put the door back on. It small fire once again picked up.
After about 10 minutes when the flames were in the front now, an erratic pulsing could be heard but it was more of an underlying noise.
I decided at this point to put the threshold back on. This helped eliminate the pulsing.
It reminded me of what a bypass does: A kick start "choke' used only to get it going.
Without this technique, having to keep the door off for the first 10 minutes to provide the extra air needed for me is sometimes not convenient, especially when I get busy in and out of the shop.
Also, because its a 'door' that is not on hinges but removed entirely, sparks could come flying out and ignite something on the shop floor, so the safety factor is something to consider.



combined-port.JPG
[Thumbnail for combined-port.JPG]
 
Gerry Parent
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Just a little update. First and foremost, I love the batch box! The J tube was wonderful for what it was but not in a place that I stepped away from for hours at a time.
- Seeing the fire has been a real pleasure too. There was never a coaling phase to the J tube which is really a nice addition. Getting down on my hands and knees to load wood and clean it though is a design feature that is going to need to be changed for a future build. I'd say around 16" from the floor to the base of the firebox would be a good height to try. Perhaps a summer project.
-  It takes on average about 10 pounds of wood per batch load leaving about 2" at the top for gas flow.
-  For the most part, within 10minutes, the stove is kicking out more heat than I could get in over half an hour with my J tube. A real bonus.
-  I was shoveling snow off the shop roof yesterday and took a few whiffs of the exhaust with my built in Testo (nose). Yep, it was mainly steam with only a hint of wood smoke smell.
-  My internal chimney stack temperatures have been higher than what I would like (almost 300F when its ripping) but I think that's mainly because my ISA of the bench/bell is only about 22 sq ft and I'm allowed 57 sq ft.
-  Tomorrow I'll probably cob in around the firebox to seal it all up and make it look more pretty with some kind of holder for the 'door' and if I have time to raise the barrel even more. UP is the one place I do have room to go without taking up more of a footprint in the shop. Perhaps this will also help to lower my exhaust temps a bit.

   More pictures to come soon.



 
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Gerry, i haven't done it myself. But been thinking about a thing. On my batch, i have a metal plate  on top of the firebox, for cooking.

Having a front door, but with that liftable top plate, to be able to reload, would be a nice adition.

I don't know if you're ever lived with a wood, or coal range. With a cast Iron top.  But that's about what i'm thinking. You lift the top rings, or rectangular plate,  to load the firebox.
 
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Satamax Antone wrote:Gerry, i haven't done it myself. But been thinking about a thing. On my batch, i have a metal plate  on top of the firebox, for cooking.

Having a front door, but with that liftable top plate, to be able to reload, would be a nice adition.

I don't know if you're ever lived with a wood, or coal range. With a cast Iron top.  But that's about what i'm thinking. You lift the top rings, or rectangular plate,  to load the firebox.


You know, as I was building the firebox and looking at the best positioning for the casserole door, I temporarily left the front-most firebrick of the roof off to angle the door enough to be able to see and load the fire much easier from above. So yes, it was going to be similar to loading a coal range from the top and not have to get on my knees to do so.
Plans changed though as I was concerned with the glass being too close to the fire (and cracking or shattering) so I replaced the brick on top and backed it off.
As for a metal plate, it certainly would be a good idea if I was cooking my meals in the shop!

Not sure if the stove would smoke into the room if it was a top loader. I guess if you slowly cracked the door open to let any smoke clear (like most wood stoves), the draft should theoretically suck it all through the port. I like the concept though.
 
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Gerry, when you reload, it's at ember stage, so not much smoke comes out anyway.
 
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So Satamax, would you suggest having a top load door be a solid insulated piece and the front be a permanently fixed glass for viewing?
 
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Gerry Parent wrote:So Satamax, would you suggest having a top load door be a solid insulated piece and the front be a permanently fixed glass for viewing?




Nope, sorry, by experience, i know that  for cleaning, it's easier to have both, front door and lid.


Mind you, i have tried a vertical batch, but it's not up to par yet.

There is several videos on my youtube page,






Watch these, and make your own mind. If you can improve on it, if you feel you like it; you're more than welcome to use it.

 
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Peter van den Berg wrote:It would be very interesting what would come out of a merger between J-tube and batchrocket technologies, given what is known about those two at this point of time. It could lead to a whole new breed of rocket heaters but although it's tickling my imagination, it won't be me to pick up development.


Satamax, This is something Peter said not too long ago. After watching your video, it seems that this is one way of combining the two: Top feed with port.
EDIT: Watched the rest of your videos...they are a year old so wondering what you meant by "not up to par yet"? Any improvements?
 
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Hi Gerry;
How long is the burn time on that bad boy?
How do you light it?  Seems, maybe I read something about lighting from the top down?
How do you load it ? Larger wood on bottom and kindling ,paper ? on top?   Inquiring minds want to know.
Will you be modifying your floor port tube to Peters style?
I know it might have snowed a skiff up there once or twice ... but you promised us more photos!
Sweeping off a little snow, PERMIES.... or sleeping ???  A no brainer there my friend:) They make boots and snowmobiles ... and sleep is highly overrated.
One must keep his Priority's straight you know!


Even though it's still months, until I can tear one of mine apart. I can't wait to get started, (this is all your doing you know:) So ...
On our next trip to Sandpoint, I'll be buying the square tube and building a floor port to Peters specifications for one of the rocket's.
I'll cut it long and trim it back to length during the build.
After that a trip up to Columbia Falls for some insulated fire bricks...
I'll take photo's and make a post all about floor port construction as I go.
 
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thomas rubino wrote:Hi Gerry;
How long is the burn time on that bad boy?
How do you light it?  Seems, maybe I read something about lighting from the top down?
How do you load it ? Larger wood on bottom and kindling ,paper ? on top?   Inquiring minds want to know.
Will you be modifying your floor port tube to Peters style?
I know it might have snowed a skiff up there once or twice ... but you promised us more photos!
Sweeping off a little snow, PERMIES.... or sleeping ???  A no brainer there my friend:) They make boots and snowmobiles ... and sleep is highly overrated.
One must keep his Priority's straight you know!


Even though it's still months, until I can tear one of mine apart. I can't wait to get started, (this is all your doing you know:) So ...
On our next trip to Sandpoint, I'll be buying the square tube and building a floor port to Peters specifications for one of the rocket's.
I'll cut it long and trim it back to length during the build.
After that a trip up to Columbia Falls for some insulated fire bricks...
I'll take photo's and make a post all about floor port construction as I go.


OK Thomas, here's the skinny on all your need to know questions...
Hard to say how long the burn time is. On a J tube, it was pretty cut and dry but with a batch, the coal phase makes it hard to say exactly when its finished. I know I'm getting the often quoted 45 minutes per batch but would be more inclined to say a little over an hour. I've been mostly closing the air inlet as soon as the wood is pretty much glowing coals with only some flame left and find that a good 2 hours later, I can still see some glowing coals. A little stir, some more wood and back in business! Oh how sweet it is....:) However, I've mostly only needed to have 2 fires a day (morning and late afternoon) to keep the shop between 55F-75F on average. So about 20 pounds of wood a day total.
I haven't yet tested the claim that a half load has the same burn time as a full batch but with only half the heat. Soon to come....

As you read, (and as I recall) Peter's method of lighting is upside down. He puts the big logs on the bottom, mediums in the middle and the kindling on the top and lights it at the top back. I can see the logic to this and tried it twice but couldn't quite get the hang of it. Right now my method (which has changed several times) is to light a small fire at the back (using a waxed cardboard box cut up into small strips and covered with some small wood bits from wood chopping) - Haven't used newspaper once like I did with my J tube all the time.
While the little fire is burning, I then make a little bridge with 2 pieces of kindling to span the bottom V of the firebox. I carefully place about 5 more pieces of kindling on top of this bridge and let them catch on fire a bit before loading the rest. Wood is loaded in layers. I think its called a log cabin style. Again, 2 pieces of little kindling placed perpendicular is used to separate the layers. I have found that if there isn't an air space between the wood, it tends to smolder a lot before it gets going producing a dirty burn. Leaving about a 2" air gap at the top, I then put the casserole door on and the draft travels right under the bridge and right into the fire at the back making her spring to life. About 10-15 min. later, the bridge collapses but the fire is well going by then so is not needed. Placing the air entrance down low has significantly reduced the amount of pulsing (Thanks Peter!), but if it does, this is when I insert Peters 'threshold' in there which eliminates the pulsing and changes the dynamics of how the air flows into the fire....... Whew! Got it? 🥴

Next question.... "Will you be modifying your floor port tube to Peters style?"   Yes. Not because I think what I have now is not working but because I just want to try his method and compare the two. I remember Matt saying in his secondary air video that its acts as a great way to keep the wood from obstructing the port and its so true. So, far it hasn't budged one iota and is holding up very well.

Tonight, I had a crazy idea while watching the fire. I kept smelling a little faint bit of smoke (in particular when the draft shifted a bit back and forth) I sniffed around and found a little smoke smell coming from around the door seal (which is just the lid pressed into the cob while it was still wet). I had some rope gasket cut to do this one day but I had a faster way. I used some leftover high temperature caulk and gooped it around the door frame. I then greased the lid a bit and stuck it back into place. A perfect seal but its really gripping the door too! Hopefully tomorrow morning I will be able to pry it off!

I know your gonna love it Thomas! The great thing about it is that we're so used to dedicating a whole chunk of time into a full build that it seems so quick when your only doing a retrofit.

Yes, yes, more photos to come for sure! Geeeze!   :) In the meantime, here is a quick video of a burn showing the stacking method and port stub at the back.


 
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Well, I guess I got exactly what I expected. I literally had to "pry it off" with a scraper and utility blade which took about 15 minutes, then another 15 to clean it. Lesson learned: Don't use tractor grease as a mold release agent! On the good side, I saw how well high temperature silicone is for sticking to not only greasy things but to sandy cob.
pyrex-lid-with-stuck-on-silicone.JPG
[Thumbnail for pyrex-lid-with-stuck-on-silicone.JPG]
 
thomas rubino
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That's the spirit Gerry!  
To try and fail is better than not trying at all!  Especially when you suspect failure is a distinct possibility.
That's why your on our rocket science team! (I haven't figured out yet, who is who in our group photo)  Always experimenting! And sharing the results!  
MIT/ Nasa  look out, we will both be at the cutting edge of rocket science ... or at the brink of disaster... any moment now:)

Famous inventor words of wisdom )    Hold my beer and watch this!
        (not scientist)
 
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Back at it last night to get a better door seal. With a dremel, I made a channel for the rope gasket to fit into then cobbed around it to help hold it in place. I also built up the cob all the way around to help hold the 'door' in place as well. In hindsight, the only (minor) thing I would have done different is before cobbing, to cover the face of the rope with some masking tape to keep it clean and give it a more clean finished edge. Took about an hour to do.
This morning it came off no problem (OH JOY!) and seems to seal much better.
During its first test fire, I didn't hear any whistling of air sneaking through anywhere when the lid was on and the primary air was almost completely shut down, nor did I smell any residual smoke as I did before.
So far a success!
rope-gasket-around-door-frame.JPG
[Thumbnail for rope-gasket-around-door-frame.JPG]
 
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A few updates to share.
For anyone interested in pursuing a casserole lid 'door', I included a few tips to consider over at this post: thrifting / thrift store stuff / thrift store shopping list(s)

I really wanted to see the splendour of the double rams horn so I took the barrel off in the first 10 minutes of a burn and took a video:



The flames came out of the top of the riser by about 2' indicating to me that it might be a good idea to give it that space by raising the barrel more. Right now the top gap is 9".

I was expecting the burn to increase in intensity with the barrel off but when I checked before and after it seemed exactly the same to me. Interesting that the barrel and bell don't seem to play any role in slowing the draft at all. Kinda weird.

Also, I got around to making a draft control device made from an old electric hot water tank skin, a coat hanger, a few washers and a spring.



air-inlet-damper.JPG
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overview.JPG
[Thumbnail for overview.JPG]
 
thomas rubino
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Sweet Gerry!  
I like those Ram horns you got there!  Really need to get a couple of those going around here.
I've got Liz's permission to create dust and havoc in her studio this spring / summer!
If I have time I'll modify the shop rocket as well.
After that...   the living room!   I Hope ...
 
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Hi all,

It has been interesting to read through the thread, especially in the beginning a lot of basic information about the floor channel and main air inlet was being spelled out with helpful details.

I am after all in the proces of understanding the basics very well as the preliminary step to building my own batch box rocket mass heater in my house.

Since you have been talking so much about the floor channel in this thread I thought it would be appropiate to ask these questions in this thread about the floor channel:

What are the precise numbers of the newest version of the floor channel found on Peter's website?    (sorry I haven't found a way to open these sketchup files on ubuntu OS yet)
("01/05/2019 A somewhat simpler construction together with a larger feed part and a higher stub, according to the latest findings.")

When I read about the numbers concerning the previous version of the floor channel I find this: "Using the steel ducts as drawn, the vertical part is 5.4% of the riser CSA and the horizontal part 8.25%. By keeping close to these percentages it is possible to calculate the dimensions for a larger or smaller batchrocket according to their larger or smaller riser CSA."

Now regarding the newest version (since Peter mentions that the the feed/horisontal part is now larger and "The feed is close to twice as large as the stub, csa-wise") is it safe for me to conclude that the horizontal part should be close to 10 % riser CSA and the vertical part of the newest floor channel should stay in the same range, close to 5 % of the riser CSA?

Also back in the days of the P-channel coming down from the 'ceiling' of the fire box Peter emphasized that the width of the P-channel should be as wide or slightly wider than the width of the port. Can we now totally disregard this rule for both the horisontal and vertical part of the newer floor channel?
 
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Hi Rune; Welcome to Permies!   Please post photo's of your build as it progresses.

I also was not able to open the sketchup files at http://batchrocket.eu/
Peter kindly gave me the dimensions for the floor channel on a 6" batch.  With what is easily available in America he suggested I use 1.5" x 1.5" tubing, laid side by side
With a 4" long port connecting them. Creating a 3" x 1.5 " floor channel. With the stub being 1.5" and half the height of the riser port. It has a flat piece welded at the top to direct the air into the riser port.
These were close enough to the metric measurements.
 
Over the next month I will be fabricating one for my stove. I will post with photo's at that time.

Peter's metric measurements were   35 x 35 x 2 mm  for the stub and 60 x 40 x 2 mm for the floor channel.
The stub has a flat piece over the top helping to direct the air into the riser

As far as your question on the original P channel.   I believe you follow the original design size parameters if building a P channel style and ignore them if you choose to build with the floor channel design.  
 
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Rune Dahlgreen wrote:
What are the precise numbers of the newest version of the floor channel found on Peter's website?    (sorry I haven't found a way to open these sketchup files on ubuntu OS yet)
("01/05/2019 A somewhat simpler construction together with a larger feed part and a higher stub, according to the latest findings.")


HI Rune,   I'm using LInux also. The easiest way I found to open a sketchup file is to go to their website: sketchup and upload your file there. I don't know if it has all the functions of having the program on your computer but so far its worked for me. I'm not the person to question about Peters design so hopefully you will find all your answers from his file or from the man himself.
If you do build one or find out any info, I would be interested as I plan on building his floor channel. Please feel free to post your findings here or start a new thread if you feel so inclined.

 
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Thanks for replying Thomas.
I think there's a way to view Sketchup files irrespective of the operating system, though. It's called SketchUp Free and runs inside a browser. Apart from that, there seems to be a SketchUp viewer app as well for mobile devices.

Edit: Now I see Gerry already provided the same link.
 
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Rune Dahlgreen wrote:Now regarding the newest version (since Peter mentions that the the feed/horisontal part is now larger and "The feed is close to twice as large as the stub, csa-wise") is it safe for me to conclude that the horizontal part should be close to 10 % riser CSA and the vertical part of the newest floor channel should stay in the same range, close to 5 % of the riser CSA?

Also back in the days of the P-channel coming down from the 'ceiling' of the fire box Peter emphasized that the width of the P-channel should be as wide or slightly wider than the width of the port. Can we now totally disregard this rule for both the horisontal and vertical part of the newer floor channel?


@Rune,
It would also be convenient to use two 1.5" square ducts side by side as Thomas already mentioned.

The newer floor channel is indeed another animal, other rules apply so the stub is narrower and the feed could be much wider than the port.
 
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Thank you all, for the replies. That is excellent, now I know more about the options for sketchup.

I just take Peter's metric measurements for the floor channel for the 6" size that you mentioned Thomas and scale up or down as needed for other sizes according to the percental difference in size. I will definately use a larger batch box rocket than a 6" (I have a big house, which can be a disadvantage sometimes).

Great tip on how to fabricate the channel with 2 pieces of steel like that, and I have also seen your pictures of that method Peter, thanks.

Also Gerry thanks, I will share any findings and future builds and experiences one way or another. I am just at the study phase, making sure I understand all concepts, meassurements and designs perfectly first. I have only started very little drawing and looked a bit at material options, prices, local building codes and stuff like that.
I also have to cut open my wooden floor, dig below frost line (at the very least 90 cm here in Denmark continental Europe) and pour a reinforced concrete foundation before I can start.

 
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My last post was moved to a Glass top range teardown
 
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Today I fabricated Peters floor channel design. I made it out of a metal bed frame I had. Just working on cutting the brick on the floor of the stove to accommodate the larger horizontal tube which is now 3" wide. The stub is about 5" long. As my port is 9" tall, it will now be feeding air just above half way instead of at the top. Will be interested in seeing how it performs. It was definitely a lot more work to make than Matt's design but it was a fun project.
Also included a photo of the first floor channel to show its condition. Definite signs of spalling but still in good shape. The stub is still the same length (which apparently gets shorter and shorter through the burn season).
floor-channel.JPG
[Thumbnail for floor-channel.JPG]
old-floor-channel.JPG
[Thumbnail for old-floor-channel.JPG]
 
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Hey Gerry;   Nice Job!  
Is that apx. 5" to the highest point of the stub or to the high point on the deflector?
 
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thomas rubino wrote:Hey Gerry;   Nice Job!  
Is that apx. 5" to the highest point of the stub or to the high point on the deflector?


5" to the highest point of the stub and to the top of the deflector is 6 1/4". Not sure if this is the ideal height but its what came out of the production.

I finished renovating the bottom bricks and installed the new floor channel today then lit her up. Way too early to tell anything for sure but it was a good burn very similar to the other floor channel. I've gotten so used to starting a warm stove that it smoked a bit out the door and had to be mindful of slowly opening the door before adding bigger wood.
So far (with both floor channels) it seems to take about 10- 15 minutes to get it totally smoke free. I think the dense bricks just suck up the heat. I think those insulated ones your going to use will get it clean much quicker.

Hard to tell in the photo but the slanted bricks along the bottom only go up to the front edge of the stub because they were too long and leaving a gap at the back. I couldn't cut them because my table saw motor has crapped out on me. Only turning very slow...I think the capacitor may be shot.

Also, even with no threshold, it barely pulsed at all. I think that low air inlet is the ticket and the threshold takes care of the rest.  
Peters-floor-channel.JPG
[Thumbnail for Peters-floor-channel.JPG]
 
Gerry Parent
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So I took apart the motor and blew out the 10 pounds of dust and powder in there! After putting it back together it worked great (dodged a bullet on that one) so I finished cutting those angled floor bricks to size.

Somewhere in this thread and on Peters website, he says that he prefers to have the fire "lit on top of the fuel pile at the back, known as "upside down firing". This method will deliver the best results." I have tried this again several times and just can't seem to get the hang of it. A few questions Peter if I may:
1) Do you load your entire batch of wood in (to within about 2" to the ceiling) then reach way to the back to light it with a long match? What I found is that its takes a while before the fire catches the wood below it when lit from the top vs starting it at the base of the stub.
2) If the door is put on prematurely after lighting from the top back (before lets say 10 minutes) does the fire die down almost to the point of going out?

An observation about running it without the threshold (which may be just rewording what Peter had said to me before). Because the main air intake is low and travels to the bottom front of the V channel, it tends to burn the wood much faster here and as a result causes the wood to angle forwards and which then is like a slide for any coals to drop down right into the floor channels inlet and sometimes obstructing it. As a result, I am going to fabricated another one tomorrow. I wonder if a small magnet would hold a flat piece of metal or it the threshold should just be welded to the floor channel? hmmmm
 
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Gerry Parent wrote:1) Do you load your entire batch of wood in (to within about 2" to the ceiling) then reach way to the back to light it with a long match? What I found is that its takes a while before the fire catches the wood below it when lit from the top vs starting it at the base of the stub.


What I do is loading the entire batch for that moment. Biggest pieces first, somewhat smaller on top of that and kindling on top of that. I tend to leave a lower level in the middle, where I place a handful of small tinder and light that with a single barbecue lighter. Most of the time 2" from the ceiling isn't enough to reach the back so in practice I light the fire halfway. This method allows for stacking the entire load, as opposed to starting low in front of the port and adding more fuel while the fire grows.

Gerry Parent wrote:2) If the door is put on prematurely after lighting from the top back (before lets say 10 minutes) does the fire die down almost to the point of going out?


The upside down firing method requires an emphasis on primary air for the first 10 or so minutes of the burn. That's why I leave the firebox door open about half an inch (one finger thick). When the door is closed too early, in some instances I've seen the fire goes down to the point that the afterburner flame pops off, literally. Results in this sense means what the Testo is making of it, on average significantly better than the other method over the course of ten burns each.
Just weld the threshold to the floor channel's feed and don't try to empty all the ashes out when you are at it. I almost never do unless I want to take the floor channel out to have a look at the bottom of the riser.
 
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Peter van den Berg wrote:...I tend to leave a lower level in the middle, where I place a handful of small tinder and light that with a single barbecue lighter. Most of the time 2" from the ceiling isn't enough to reach the back so in practice I light the fire halfway. This method allows for stacking the entire load, as opposed to starting low in front of the port and adding more fuel while the fire grows.


Leaving a gap was what I was missing. I like the fact that you can load it all at once doing it your way. Definitely will try again (and again) until I get it right. Perhaps this will help reduce the smoke at the beginning of the burn as well.

Peter van den Berg wrote:The upside down firing method requires an emphasis on primary air for the first 10 or so minutes of the burn. That's why I leave the firebox door open about half an inch (one finger thick).


Since my door is not on hinges, the casserole lid is either on or off. I'm not worried about sparks flying out, small children, pets etc. so unless its important to have only a certain amount of extra primary air, I'll leave it off until it gets going.

Peter van den Berg wrote:Just weld the threshold to the floor channel's feed and don't try to empty all the ashes out when you are at it. I almost never do unless I want to take the floor channel out to have a look at the bottom of the riser.


I made a temporary one with thin metal this morning with bent flaps on the bottom and sides and a magnet at the bottom but it still just wouldn't stand up properly.
Time to get into a thicker metal and make it simpler and permanent.

How close can the wood be placed to the stub? Right up to it or best to leave a gap for air flow?
 
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Gerry Parent wrote:How close can the wood be placed to the stub? Right up to it or best to leave a gap for air flow?


Right up to the stub is OK no problem, air flow is going around it anyway. Left and right of the stub the fuel could be shoved in right up  to the rear wall although a small gap would work slightly better so the fire is able to work itself down close to the port first.

What I do as a habit: I shove logs in until it touches the rear wall and pull it back about an inch. Please don't be too religiously regarding this, it's just a way to make sure there's some space there. Sometimes a piece is too long for this method so I let it touch the rear wall anyway.

Shoving a piece, however small, into the port will disrupt proper gas flow in port and riser which will inevitably lead to smoke out of the chimney stack. Visable smoke inside the firebox isn't uncommon, as long as the afterburner flame is raging it will be taken care of by that.
 
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Peter,  I think I remember reading something about you saying something over at Proboards.com (which I can't find right now) that flames that come out of the riser are not the most ideal situation. If this was you that said this and is a correct statement, could you elaborate on it a bit and what could be done to make it more 'ideal'.

I wonder if the flame would be still this high when the barrel is in place?

I took a quick video showing my system with flames of about 16" on average shooting out the riser.

 
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Gerry Parent wrote:Peter,  I think I remember reading something about you saying something over at Proboards.com (which I can't find right now) that flames that come out of the riser are not the most ideal situation. If this was you that said this and is a correct statement, could you elaborate on it a bit and what could be done to make it more 'ideal'.


We are entering fundamentals here, largely untrodden territory I might add. In an ideal situation combustion is all over and done within the confinement of the riser. Flames out of the riser isn't a good thing: compare it to a candle flame. What happens there is that the oxydizing of the combustible material only takes place at the outside of the flame. Inside there's no oxygen so therefore no burning.

Flames out of the riser usually are oscillating, in a split second it comes up, goes down and up again. Looks like it's doing right, after all it isn't like a steady candle flame is it? But outside the riser the temperature is much, much lower and therefore one of the conditions in order to achieve complete combustion isn't met anymore. I didn't come up with that by myself, the Testo teached me that flames out of the riser aren't as good as one might think. Lots of carbon monoxide and some smoke as well are released into the outside air. Apart from the fact that smoke is wasted fuel it also becomes a pollutant, we shouldn't allow that to happen.

And no, the flames won't be that high when the barrel is in place, since coaching the gases into a 180 degree change of direction means friction. The larger the top gap, the less friction seems to be a good rule of thumb.

Now how to counteract this effect, adding friction isn't something I am particularly fond of, quite the opposite. But during development of the DSR2 I learned another thing: the end of the riser, expansion room or whatever you like to call it can be made smaller than system size. Just a bit more csa as the riser port seems to do the trick, any smaller than that and the whole thing became very sluggish. The maximum gas velocity in the riser port seems to be limited by the end port, combustion goes on in a less violent way and CO production is very low.

This effect of the above is largely not understood yet, it has something to do with expansion of gases between riser port and end port. While fiddling with the DSR2 I tried restricting the top of the extremely short riser and the whole of the thing stopped working the correct way entirely. It looks like there need to be some sort of expansion room between those two ports. The overall effect is an afterburner flame that stays largely inside the riser stub. Running full tilt the flames are entering the expansion space but tend to stay at the rear half due to the stumbling block halfway the expansion room's ceiling.

In case this end port thing is one of those effects dictated by laws of physics it might work on a straight riser as well.
I need to stress this is pure speculation, I didn't try this with a straight riser as yet so the waiting is for somebody to try it out.
 
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