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Post by sksshel on Apr 14, 2019 5:01:40 GMT -8
Can an "original DSR" be upgraded to incorporate your new findings? I have a 6" DSR with the top port out of the burn chamber into the upper shoe box. (no riser). In an earlier version of the Mark II, you used an expanded port size along with changes to the secondary air tube. You also included a "Trigger" in the shoe box. Have those been eliminated as viable options?
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Post by peterberg on Apr 14, 2019 5:58:41 GMT -8
Right now we have a 150mm system which in the coldest times of winter needs two or three consecutive fires to warm the house the way my wife likes it. The step up from 150 to 200 mm is huge, capacity of the firebox goes up from +/- 6 kg to +/- 14.5 kg. So capacity is more than doubled this way, it might be sensible to reconsider size. Upgrading to 180 means capacity would be up to +/- 10.6 kg per burn. All depends on what is acceptable: 2 days of three fires, 4 days, a week? When you say cant avoid refractories is it because other material will break or is not accepted? Other material could break, thermal stress would be greater in a larger combustion core. My development core is entirely built out of insulative heat resistant materials, although not the highest specced. The top bricks of the upper box tend to crack due to heat related stress. There's also one hard firebrick there which is holding up admirably. I dont have proper refractories but I have tested making the gap with available bricks and it works well from what I see. That sounds good to me, maybe you could build it in such a way maintenance would be easy? I have thought of the cooktop and ours is about 980mm right now. It should be in an acceptable range. You are right, it would be still in an acceptable range, maybe even lower. |
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Post by peterberg on Apr 14, 2019 6:04:29 GMT -8
I tried making my own refractory mix for the stove we have now but it did not last and cracked too bad to use. So I wanted to try plain brick and cut thin splits to put in place of the old firebox. They show no signs of wearing or cracking, which has been so nice. Also the port is cut into a brick. Just being put in place with thick clay slip this seems hopeful to me. You might be lucky those bricks are of the soft type. Those tend to get harder when subjected to high temperatures, shrinking in the process. Has the colour of the bricks got lighter by now? |
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Post by peterberg on Apr 14, 2019 6:26:54 GMT -8
Can an "original DSR" be upgraded to incorporate your new findings? Maybe yes, maybe no, I am unsure about that. The depth of the firebox is different and also the cross section area for example. Riser and top box proportions are important, more so than the firebox. I have a 6" DSR with the top port out of the burn chamber into the upper shoe box. (no riser). In an earlier version of the Mark II, you used an expanded port size along with changes to the secondary air tube. You also included a "Trigger" in the shoe box. Have those been eliminated as viable options? The end port has been at a number of different sizes, yes. The top box size also, all those preliminary sizes didn't cut the cake in terms of reliability. I can't remember using the term Trigger but maybe you mean the trip wire? It is replaced by what now is called the "stumbling block" or "stumbler", yielding much better results overall. All those other configurations were mere tries and more tries (accompanied by lots of sighs) to find a good setup which is also, most importantly, easy to build. In short: all those other features aren't part of, or leading to, the current end result. |
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Post by travis on Apr 14, 2019 7:12:50 GMT -8
Right now we have a 150mm system which in the coldest times of winter needs two or three consecutive fires to warm the house the way my wife likes it. The step up from 150 to 200 mm is huge, capacity of the firebox goes up from +/- 6 kg to +/- 14.5 kg. So capacity is more than doubled this way, it might be sensible to reconsider size. Upgrading to 180 means capacity would be up to +/- 10.6 kg per burn. All depends on what is acceptable: 2 days of three fires, 4 days, a week? One other consideration was the way I buck my firewood. It would fit very nicely moving from 150 to 200, but this comes from more of a desire to remove funny rounds of wood that end up 20 or 25cm which are awkward to burn and just plain annoying on some days haha. I will definitely think about this and it may be better for all around workability. |
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Post by travis on Apr 14, 2019 7:15:45 GMT -8
I tried making my own refractory mix for the stove we have now but it did not last and cracked too bad to use. So I wanted to try plain brick and cut thin splits to put in place of the old firebox. They show no signs of wearing or cracking, which has been so nice. Also the port is cut into a brick. Just being put in place with thick clay slip this seems hopeful to me. You might be lucky those bricks are of the soft type. Those tend to get harder when subjected to high temperatures, shrinking in the process. Has the colour of the bricks got lighter by now? Yes it has a little bit. Is this a good thing? |
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Post by smartliketruck on Apr 14, 2019 8:15:36 GMT -8
Stumbling block as opposed to trip wire! Nice term, I'll use that from now on if you don't object. I could share this file, yes, but it's a principals drafting, not a real-life drawing utilizing real-life materials so material thickness won't be correct, for one. In short: it isn't a reference design, that's more than a couple of months away, for sure. I'll dub the file "DSR2 RC1", meaning "Double Shoebox Rocket mark ll release candidate one". Edit: The file can be downloaded using this link. It's in SketchUp version 8, the lowest commom denominator. Stumbling block just seemed natural, I'm glad that you and the voices in my head agree  Thank you for posting the sketchup file.
I was dry stacking 9" x 4.5" x 1.5" splits and the natural size of a simple 3 brick deep splits firebox works out pretty close to a system size of the 120mm you are working with. Closer proportions were needed before getting out the saw for the top end.
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Post by peterberg on Apr 14, 2019 8:22:44 GMT -8
You might be lucky those bricks are of the soft type. Those tend to get harder when subjected to high temperatures, shrinking in the process. Has the colour of the bricks got lighter by now? Yes it has a little bit. Is this a good thing? Yes, it is. It means the bricks are getting harder and hopefully also stronger. |
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Post by peterberg on Apr 14, 2019 8:29:33 GMT -8
Thank you for posting the sketchup file. I was dry stacking 9" x 4.5" x 1.5" splits and the natural size of a simple 3 brick deep splits firebox works out pretty close to a system size of the 120mm you are working with. Closer proportions were needed before getting out the saw for the top end. Splits are material thickness enough for such a small system. I'm curious what it looks like when ready for takeoff. The sheer power of my small development model might be just right for a cooking stove or space heater in a moderate climate. |
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Post by travis on Apr 15, 2019 18:26:54 GMT -8
Peter my wood comes in logs of 150cm in length. I had hoped to do two cuts and have 50cm rounds. Could I scale the 180mm model up just slightly to fit this into the box without trouble? Say a base of 135?
Edit
As I have continued searching longer i decided to go back to the batchrocket site and found a very surprising number. The base for length of the firebox may be up to 5.5 times base. Is this still true? If so I am very pleased!
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Post by peterberg on Apr 16, 2019 1:17:58 GMT -8
Travis, as far as I know this is still true. I don't remember the 5.5 times base thing though, when asked for I always replied a 25% extension in depth is possible and reliable. One thing is, lighting the fire in front of the port is getting harder when the box is deeper. In order to get away with 500 mm fuel length you'll need a 600 mm deep firebox.
It would be entirely doable to build a 180 mm system and extend the 520 mm firebox depth to 600 mm or even more, no problem.
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Post by travis on Apr 16, 2019 7:53:04 GMT -8
This is great news! The gap to cover the roof will be very easy with two of our standard clay bricks and with a less wide box it should be more sturdy in the long run. I am excited to try this design in our home.
Once again thank you Peter, your work is an inspiration!
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Post by esbjornaneer on Apr 27, 2019 1:59:46 GMT -8
Peter is there any advantage of the 'stumbling block'/'hanging brick' being a full brick thickness rather than a split? I know it may affect combustion compared to your tested results... and should a split in that case be placed
1) 250mm from the back wall of the afterburner like the full brick,
2) central in full size brick, or
3) at the trailing end of the full size brick?
Only asking as you said it is very important to get the location right for it. And thinking that it may be good to have less mass?
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Post by peterberg on Apr 27, 2019 4:59:13 GMT -8
Peter is there any advantage of the 'stumbling block'/'hanging brick' being a full brick thickness rather than a split? I know it may affect combustion compared to your tested results... and should a split in that case be placed 1) 250mm from the back wall of the afterburner like the full brick, 2) central in full size brick, or 3) at the trailing end of the full size brick? Only asking as you said it is very important to get the location right for it. And thinking that it may be good to have less mass? Oops... I am not sure what you mean so I'll give you the dimensions I used. The stumbling block as it is now has been done in two sizes: 25 mm high and 63 mm wide seen in stream direction, and second 25 mm high and 54 mm wide in stream direction. The second was done in hard firebrick since my last insulating firebrick broke up in half a dozen pieces. Results seemed unchanged so the width is still within critical limits I'd say. There's a marked difference between a block or a trip wire though. The block version is the stable one of the two. Location of the different parts: the stumbling block is centered in the depth of the top box, so center of box and block are at the same location. The end port is centered in the front half, it has been different now and then but I think this is the best location. I'd say the block need to have a certain minimum width in order to work as intended. A block with dimensions 25 mm high and 25 mm wide isn't advisable in that case. Something tells me that's what you meant, yes? To answer your last question, I don't think mass is an issue in this case. Part of the rear half ceiling is hard firebrick now and nothing has been changed results-wise. I'm gearing up for building the hard refractory reference design, within a month (or maybe two) we'll know whether mass in the core makes a large difference or not at all. Or something in between. |
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Post by esbjornaneer on Apr 27, 2019 6:19:16 GMT -8
2.9.1.0 Thank you for this clarification, it is great and super clear!
While what you are saying they should be  Thank you again.
2.9.1.0 |
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