Development of a compact core, provisional title "Shorty".

[independentenergy]

was the aluminum tape used to close the vents on the uprights?
do you think there is too much air cooling the core at startup?

[peterberg]

Dec 30, 2023 9:54:38 GMT -8 independentenergy said:

was the aluminum tape used to close the vents on the uprights?
do you think there is too much air cooling the core at startup?

The tape was used to check whether there was too much air supply. In a short test it came out as too little instead. In order to keep the burn stable, the air inlet should be tailored to full burn. More opening is needed at startup, air supply is a combination of opening and air velocity. The more draw of the chimney, the higher velocity. That's why I start the thing initially with the door open a crack.

[peterberg]

Since last year, there are some new developments. Yes, really, there are! First run of the new year was done with small planks, 22 of them, with a layer of charcoal beneath it. The port configuration was still the same as before, 60/100%. The 60% for the riser port, 100% for the end port. Too much wind, 5 Bft and gusts, resulting in a just so-so burn.



Not a very succesful testrun, not bad either. I let it sink in for a day, what to do next? It would be nice to get a more consistent and stable burn, something one could rely on. Maybe the warming up phase could be shorter and to this end, the top of the riser box should be hot earlier. Still no insulation on that top, nor the sides of the box that rises above the firebox.

Best I could come up with is to shift the end port down a bit, possibly more heat could be captured in a shorter time span. Maybe even better mixing of the burnables and fresh air.
Puzzling around for some time, how to do it with the resources I've got in the workshop. Bits and bobs, strips and small pieces of the ceramist's kiln shelfs. I managed to get it done and I was quite content with the result. End port is now 100% of chimney csa, and in the same changing mood, the riser port was changed back to 70% as well.



The end port shifted down about 40 mm (1.57"), it could be more but that remains to be seen. Actually, it did look quite smart, sitting in the barrel like that. Not an idiot's contraption, anyway.



I loaded the thing up today in the morning after coffee break, had some difference of opinion with the Testo 300, lit the fire and waited what would happen. Wind force 3 Bft, nothing to be worried about.



As can be seen, there's small planks all over, overlapping and pairing two at the time in order to simulate larger pieces. The burn was a bit adventurous, first I forgot to set the draft limiter in action so the draft of the chimney got pretty strong. At 15 minutes into the diagram I noticed the error and set the limiter in action. This resulted in a lower draft but the oxygen level started to decrease almost immediately. This is a bit strange, normally more draft means the fire is ramping up so less draft should deminish the fire somewhat. But oh well, the CO got down as well so no worries here.



In order to check whether or not my conclusion was valid, I'd put the limiter out of action at 17 minutes. The O² level reacted almost immediately and also the end temperature. So I freed the limiter and both went down again. From that moment on I did nothing to influence the process, I just let it go. At about 37 minutes the top of the burn was reached, the O² went down briefly to 5.8% and that was it.

So what happened? Delivering more fresh air to the fire did not result in a more fierce burn, rather the opposite. This could mean that a stronger draft than the 12 Pascal of the EU test could trigger a cleaner burn. And also a lower efficiency as a consequence. The white Testo filter came out light grey as usual, CO has been below 500 ppm for 32 minutes, more than half of the entire burn. Starting up from cold and completed with a tailout to 3.6% CO².

I am very satisfied, it looks like this could be a turning point. Don't hold your breath, tomorrow another burn is planned to verify this wasn't a one-off. And I need to verify this results using hardwood species as well. Interesting times again!

[peterberg]

Since Januari 4th, I've ran the development model three times. On the 5th, a full load of softwood planks. Nothing remarkable, smoothly and maybe a little bit too low in oxygen at some point but no overfuel at all. No surprises here, just a burn without worries.

On the 6th, I tried a testrun with hardwood again. Still not dry enough, 20% moist. The burn couldn't get upto speed and I had to poke now and then, turning pieces over. Probably too tightly packed, not a nice run and the average CO level was beyond the EU norm. Not good, the thing is clearly much happier with really dry fuel. Unless... the moist pieces were added on a glowing hot coal bed.

On the 7th, I decided to have another try with the moist oak. More loosely loaded this time and I kept the fuel just not higher than the port level. This measured testrun happened to be number #51. All three testruns described here produced light grey instead of black Testo filters.



It looked good but the core wouldnt play ball. Coming up very slow, no poking required though. It definitely isn't a good idea to use moist fuel for a cold start and than expect to turn out into a good burn. Because the burn was spoiled anyway, I added two pallet bobbins on the large, hot coal bed.



Keep in mind, the effect of adding fuel in a standard batchrocket would send the CO level to the sky in a towering spike, accompanied by visable smoke from the chimney. And also, correcting itself in about 5 minutes, sometimes much more.

Not this time though, both oxygen and carbonmonoxide went down, steeply. See the following diagram, the refill was done at the 55 minutes mark.
Watching this, the thought of "this is too good to be true" came up very quickly. So a check was in order, another bobbin was added at the 71 minutes mark. Same behaviour, both lines came down again, although half as much as the first time. Seems logical to me, half the amount of fuel, half the wood gas production.



In conclusion: adding fuel is working extremely well with this core. The riser box in this configuration seems to be capable of handling a temporarily overload without problems. Something similar happened just a month ago, published on December 20th. Four pieces of moist oak were added and the CO and O² lines came down, although not as obviously as yesterday.

[fruitbat]

Thank you for the ongoing experimentation and updates Peter. I know there is still some way to go, but the good behavior on refueling coupled with the low height will be of great value in cooking applications...

[peterberg]

Jan 8, 2024 8:45:19 GMT -8 fruitbat said:

Thank you for the ongoing experimentation and updates Peter. I know there is still some way to go, but the good behavior on refueling coupled with the low height will be of great value in cooking applications...

Or just a shop heater like the three barrels tower, running it all day long in a large shop...
Not to mention the possibilities for a low main bell and a huge bench...

The height profile is even lower than the DSR2 or 3 versions plus the core exhaust isn't directed upwards.

[peterberg]

The devil is in the details, it surely is.
One testrun a day is possible, not more than that because of the passive nature of our house. Otherwise all doors and windows should be open for hours in order to get rid of the excess heat.
The testrun of Januari 12th was done the classical way. Small fire in front of the port and once that was going a full load on top of that. Not bad at all, so another test could be coupled, adding three big pallet bobbins while the coal bed was at its hottest. It shows that refilling could be overdone, a high and narrow peak of CO rose up. It lasted for two minutes and corrected itself without a hiccup.



One item on my to-do-list was a narrower end port, just to check what effect that would have. A modification also suggested by a member of the Dutch Ecologieforum. With some effort I could manage it to restrict the port to 89%, close enough to the 90% goal.



It didn't look like much less as compared to the former situation, though. The batch was loaded a bit sloppy, not as compact as I was used to. Remember, this is softwood and very dry, less than 10% so it did catch fire very quickly.



The O² went down all the way to 4% and stayed there. I tried to supply more oxygen by opening the door, to no avail. This clearly was not what I wanted, although this wasn't an overfuel situation it looks like to be on the very brink of it. Not good, so the following day I opened the barrels up again and took the modification out.

Measuring the formerly used pieces it dawned on me that the opening hasn't been 100% of chimney pipe csa, just 95%. In order to get it right this time, with the help of some firebrick crumps and stove caulk I managed to end up with an exactly 100% end port. Pfhew!



The following run was exactly what I was aiming for, very stable, O² just above 6% and no peaks. A little bit high end CO but oh well, part of the game sometimes.



Today I planned another testrun, a smaller load, same bone dry fuel, and more densily packed. Also good, no trouble at all. Good numbers and no overfuelling, far from it. Measured testrun #56.



This is the latest state of affairs. Normal top lit batches should be no higher than the top of the port and some space between the fuel and the rear wall. Next attempt would be a testrun using hardwood species. The moisty oak might not be the best choice but that's what I have laying around.

[capscut]

Thank you for your continued refinement of these stoves Peter! Are you happy with the shift down of the exit port on this design with the 100% size?

I'm curious if it created a similar result as the stumbling block you used on an earlier design?

I really like the simplicity of this stove and the use of the ceramic kiln shelves should make it easy and less material costs.

[peterberg]

Jan 20, 2024 12:39:33 GMT -8 capscut said:

Are you happy with the shift down of the exit port on this design with the 100% size?

Yes, very. Heating up of the afterburner is much quicker.

Jan 20, 2024 12:39:33 GMT -8 capscut said:

I'm curious if it created a similar result as the stumbling block you used on an earlier design?

To be frankly, I didn't look at it that way. But you could be right, lengthening the hot gas path is what it is doing, among other things.

Jan 20, 2024 12:39:33 GMT -8 capscut said:

I really like the simplicity of this stove and the use of the ceramic kiln shelves should make it easy and less material costs.

The ceramic kiln shelves are pricy, much more so than firebricks, I'm afraid. But on the other hand, the shelves are still in one piece while other parts like most of the 30 mm firebrick slabs are cracked or fell apart. No wonder though, experimenting as I am doing is murderous for anything firebrick.

[peterberg]

After a generous pause, I picked up development again. This post is just about one aspect, the air inlet. The main and also only inlet is, compared to system size, about 42%. This run is done with the inlet restricted to 27.7%. That's a little bit less than the gross section area of both the rectangular tubes of the door posts together. Still, it is a wide slit, 160 mm (6.3") wide to be precise.



It looks a bit rough and it is, though good enough for the experiment. One effect could be that the burn is slowed down a bit. But on the other hand, very low oxygen levels could be reached earlier, with overfuelling as a consequence. In order to promote the likelyhood of such a situation, very dry (8.5%!) soft wood was used.



Every testrun is started from cold so all burns are comparable with each other. It came up rather slow, door was closed at the 11 minutes mark. Oxygen level went very low, past the "better to stay above" level. The burn got unstable as can be seen, but no sign of overfuelling nor thermal runaway.



Looks positive, next run probably with some pallet bobbins and the air inlet not as a slit but as a rectangle, roughly 1 to 3 ratio I'd think.

[peterberg]

On Februari 3rd and 4th a testrun was done on both days. Both failed miserably, not because of the dreaded overfueling but due to the Testo software on my old(ish) laptop froze solid instead. Both occasions the data was lost and the Testo 300's vacuum pump kept running, even when switched off. So the tedious chore of taking six Torx 1 screws out and disconnecting the battery's jumper from the main board with long-nosed pliers had to be performed twice.

The testrun on Februari 4 looked quite good though, for the first 8 minutes, that is. The CO was decending in an early stage and from the 4th minute onwards both CO and O² lines moved congruently real nice.



Another attempt has been done on Februari 6th, hoping for the best. The Acer netbook is really old, bought in the same year, 2009, as the now defunct Testo 330-2. It is still running on Windows 7, never had any updates since 2011 because I switched the wifi off in order to keep it from updating while I was running a test (very annoying!). It might be too slow for the recent Testo software although Windows 7 is specified as the lowest version to run it on. I have to think it over to buy a new or refurbished laptop of somewhat more recent make.

However, the test went well, despite unfavorite circumstances like wind 6/7 Bft with strong gusts upto 8 Bft. The load consisted of small softwood planks only, fairly compact stacked for this occasion. Also visable is the restricted air inlet, 30% of chimney csa and 3 to 1 width/heigth proportions.



The test itself wasn't as nerve wracking like some others, surprisingly enough. The lines shows how frequently the gusts were coming but both the CO and O² lines didn't make any less favorite jumps. End temperature went too high for my liking, also reflected by the lower efficiency. The barrels are somewhat too small for this core, or the exhaust opening could be placed lower.



Not bad at all, we are going along quite well so far. I think another testrun is required, during calmer wind circumstances, just to check whether the air inlet wouldn't be too cramped now.

[peterberg]

Another testrun done, six days ago. Yes, I know, it's a bit late but here it is. Configuration the same as last time, fuel softwood planks again. Only difference: windforce 2 beaufort instead of 6/7 Bft last time.



Fire development went slow(ish), at 20 minutes into the burn the afterburner was on the verge of popping off. But another part of the load catched fire shortly after and it went back to brisk business again. Altogether, I fully expect this core would be able to handle larger pieces of fuel quite well.



Although the bump in the CO line don't look nice, the numbers are quite good.
Averages: O² 13.03%, eff. 87.23%, CO 702.1 ppm, Tr 140 ºC.
It looks like the burns in this core remain stable now for almost all situations. Noteworthy though, the overall efficiency don't show much fluctuation through the whole range of test results.

Perhaps I might do another testrun before weekend, I recieved a newer laptop from a member of the Dutch Ecologie Forum. The temptation to try this out is surely around the corner. Coming weekend I am off to Belgium, attending a workshop, making sure noses are all in the same direction. One could call it conducting a workshop, but probably this is too strong a term.
During this workshop the first implementation of a bell construction under a concrete staircase powered by a Shorty core will be built. I'll be busy with taking pictures as well, of course, some will appear here as well.

[peterberg]

The Belgium workshop has been completed about two weeks ago. The last 1.5 days I happened to be the only one there with experience in masonry work. Sufficient to say, I was completely knackered when I got home. I slept half of the days for the next week and I am still not fully recovered. Getting feeling better now, it's about time. Loss of energy is the fate when one is approaching 80 years of age...

But... I learned some new things!
For one, the required refractory slabs weren't all there. I used a trick I just learned from Glenn Littman, he's publishing his build (permies.com/t/238503/Batch-Rocket-Build#2212309) on the permies forum. This is a way to use a steel support structure filled with firebricks only, to create a flat surface to build the core on.





The second novelty was the very first upscaled (from 5" to 7") Shorty core. It worked after some insistence, so there's a real chance also this variant is fully scalable. And a second "B": the bare core worked without a chimney of any kind. The picture shows the core, all around lots of water vapor, but the exhaust opening doesn't show any smoke.



To round it off, the whole of the construction is what in Austria is called 'a triple skin heater'. The core is the first skin, the single skin bell around it is the second, and the masonry-and-lintel staircase around it is the third skin. On only one side (the front) the third skin is following the shape of the second one. Everywhere else, on the sides, rear end and top, the third skin is 10 to 50 cm (4" to 1/2 a yard) or more away from the actual bell.
No picture to show this, sorry, the staircase is still in building phase at this time.

[independentenergy]

Welcome back Peter, I'm sorry for the overwork you had to put up with.
In your setup it looks like the core was not isolated?

[peterberg]

Mar 6, 2024 23:59:55 GMT -8 independentenergy said:

In your setup it looks like the core was not isolated?

No insulation around the core, that's true. Due to larger core bricks than anticipated by the bell designer there wasn't sufficient space for the 25 mm blanket that was available. The rear wall could be insulated and about 25 cm on the right side. After a lot of deliberation we left that out. Regarding the top end of the riser box: this will heat up quite quick anyway, because of the split firebricks and thin top slab.