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

[fruitbat]

Dec 13, 2023 4:06:49 GMT -8 peterberg said:

In order to make the exit port round I would need a watercooled diamond drill so a hole could be made in the kiln shelf.

I was thinking of vermiculite board, which would be easy to cut a round hole in, and enlarge for further trials.

But quite agree, it's the wonderful simplicity and ease of construction which makes this design outstanding.

[peterberg]

Dec 13, 2023 4:40:59 GMT -8 independentenergy said:

I wrote it wrong.
My idea is to add two pieces of superwool to the sides of the door, two on the right and two on the left, and leave only one piece of wool on the back.
extend the depth of the door so that if it was previously 3 cm by adding two 2.5 pieces of wool it will become 8 cm

If I would do that, the lower riser part will be much more cramped than before. Thanks but no thanks, there are lots of ways to change the current, most succesful configuration. I'll follow my own way from now on, each and every test cost money. Not to mention the wear of the measure cells, more frequent dirty burns brings the replacement of a €500 O² or CO cell in sight earlier.

Would you please use the word "port" for the opening between firebox and riser box instead of "door"? I found it highly confusing.

[peterberg]

The effect of the thinner firebox' back wall kept nagging me. I reinstated the superwool on four sides of the riser box, a bit over an inch (30 mm) higher and also crossing the port.



I tried four testruns in total, some were really nice but half the runs were not cutting the cake. All were loaded with the same fuel and the same pattern was mimicked.



The following diagram happened to be a good one, the results of the one next day were disappointing, to put it mildly.





What the heck was going on? Still, the thought of why the less deeper port was yielding bad results kept following me. But today it dawned on me: since the shallower port generated bad results, would a deeper port generate better ones? After all, such an effect would be a sliding scale, rather than an on-off switch. So the inplementation of a deeper port was suddenly a thing to do right now.
In order to keep the bottom of the riser box as a square, I took out the wool at the rear wall and added the same amount at both sides of the riser port. What actually happened was that the bottom half of the afterburner shifted one inch (25.4 mm) to the back. Now the depth of the port rose to 8 cm (3.15"), exactly what Independentenergy was asking for, although the riser floor remained a square.



I used the exact same amount and type of fuel as before, arranged in the same manner. There was more wind today, 5 Bft with strong gusts, normally not a good omen for a succesful run.
And this were the results, surprising to say the least.



As can be seen, the O² went down rather quick. I closed the stove's door at three minutes into the diagram and refrained from doing anything else than looking at it, biting my nails (figuratively speaking) and hoping for the best. At the 3.5 minutes mark the CO dropped lower than 500 ppm and stayed there until 45 minutes. A run with a length of 57 minutes and CO below 500 ppm for 41.5 minutes is something that I rarely see, I tell you that. On top of that, the white Testo filter came out very light grey instead of very black!
Average numbers for this run: O² 12.09%, eff. 87.47%, CO 307.9 ppm, TR 146.27 ºC. The CO level for an entire run, ended according to the EU norm and compensated for to the 13% oxygen level would be 286.35 ppm. Now waiting for a day with calmer weather conditions in order to verify whether this was a one-off or new, stable behaviour.

[independentenergy]

Very good!

[andrewb]

That was a nice run that keeps us experimenters pressing on! exhilaration.

Question Peter

Was the end port opening at the front, on same side as the port and opening area at 100% system size area like earlier in the thread?

[peterberg]

Dec 18, 2023 16:49:41 GMT -8 andrewb said:

Was the end port opening at the front, on same side as the port and opening area at 100% system size area like earlier in the thread?

Yes, it was. One change at the time, so all other aspects were the same as before.

One idea that might be worth trying out is moving the end port from the top to the front of the riser box. That way, there won't be much space required above the core to function properly. This might be a real advantage for people who want to build a cooking range powered by this core. Just a brainwave, noted on my list of things-to-try.

[independentenergy]

just a curiosity, while the bottom of the rise-box is decisive for the performance of the system, have you noticed that the riser must also have precise dimensions besides obviously the end port?
for the riser have you respected the dimensions equal to the core for now?

[peterberg]

Dec 19, 2023 4:03:25 GMT -8 independentenergy said:

just a curiosity, while the bottom of the rise-box is decisive for the performance of the system, have you noticed that the riser must also have precise dimensions besides obviously the end port?

Of course, I knew this beforehand. I reasoned that the volume of the riser probably should be equal to the normal straight riser. For that, I took the 10B riser, square, and mimicked the volume in the shorter one. The riser box has been lower than it is now, higher as well, I am just searching what would work. At the moment it is 5B high and the volume is around a square 8B straight riser.
All to be read in this thread.
The rectangular riser has been tried, as long ago as 2012. Results were not as good as with a octagonal riser and the square one came much later.

Dec 19, 2023 4:03:25 GMT -8 independentenergy said:

for the riser have you respected the dimensions equal to the core for now?

I am unsure what you mean. The riser box is square, as wide as the firebox. At the moment results are good, for simplicities' sake I won't change that in the forseeable future.

[independentenergy]

everything is clear Peter, you have to excuse me if I can't express myself properly, English is difficult for me

[peterberg]

Despite the fact that yesterday wasn't a calm day, I simply couldn't wait to re-test the succesfull configuration of the day before. Wind force 5 Bft this time, no gusts. The new Testo is able to measure chimney drag during the whole of the run. Which shows that the draft limiter which is still there isn't really able to keep the draft within limits. What I am aiming for is 12 Pa, plus and minus 2 Pa, equavalent to 0.12 millibar. But the draft tend to increase upto 22 Pa in gusts, the limiter is ehrrmm... limited.

Anyway, the firebox was loaded with 2.8 kg (6.17 lbs) of soft wood species, same pattern and so on, lit on top as nearly always. (This part tend to get a bit boring.)



Upto 18 minutes into the burn the pattern of the day before seems to be repeated. No high start peak in the CO line and the O² dropped quite steep. But around the 20 minutes mark the oxygen level went lower than the 5% mark and the CO level came up. As could be expected, critical point in almost every run is around that mark. But it didn't get very high, corrected itself and was back again below 500 ppm in three minutes. This peak was almost certainly due to tunnel formation through the fuel pile, always lots of CO in that situation. Good run, not a stellar example, but a good run.
Average numbers for this run: O² 11.37%, eff. 88.45%, CO 542.6 ppm, TR 143.77 ºC.



After the test was ended I checked the Testo filter as I always do, and this came out as very, very light grey. Having oak hardwood at hand, recently purchased but still 25% moist, I couldn't resist the temptation to do a small reload, just to see how the core would react to this. So I shoved four (smallish) pieces into the firebox onto a glowing coal bed, closed the door, took a snapshot of the fire and started the Testo again.



The new load catched fire almost instantly, but probably since the pieces were so damp inside the burn didn't get very hefty. But still, quite nice and it was a joy to see the oxygen level dropping down while the carbon monoxide level reacted moderately and went on to lower levels. Surprisingly enough, this run was still within the limits of the current EU norm.
Averages for this run: O² 13.47%, eff. 84.01%, CO 741.3 ppm, TR 168.81 ºC.



Today's a windy day again, I'll try the same softwood run again and see how it goes. I'll report back about what the results are.

[peterberg]

To cut a long story short: the results are outstanding, stability is excellent. Windforce 6 Bft with gusts is not a good omen for a succesful burn but the core remained rock stable.

Not-so-excellent is the stability of the Testo's software, it crashed and I was not able to retrieve the data (again). I lost probably the first 15 minutes of the burn because of this, mainly because the vacuum pump of the Testo kept running. I had to decouple it, turned it over, 6 Torx screws had to be removed, opened up the device and decoupled the battery from the main board. This is the only way to stop the pump in this situation.

Then the battery needed to be connected to the main board again, the lid had to be closed and the screws placed back, coupled it to the probe again and started it up. Pfhoei! But anyway, not every expensive piece of equipment is bug free, let's call it that.

Back to the results then, I was very pleased with what I saw. The gusts are visable in the green oxygen line, it wobbles quite a bit. But the average numbers were eventually good enough to pass the EU norm. Bar the numbers for fine dust, I am not able to measure those because the device to do just that is horrendously expensive.



I'll do some more tests, using oak when that's dry enough. And configuration-wise, a different exit from the core, also known as end port, but that's for later on.

[peterberg]

Rummaging through the data I stumbled upon the notion that with less wind the core seems to struggle with what could lead to a fuel overload. On December 23rd, 5 Bft with gusts the diagram looked like this:



Too much CO to my liking in the startup phase but the filter came out light grey. December 25th (can't stop thinking about it, you know) happened to be a day with 3 Bft. Same configuration as two days earlier, same fuel load as well. But a very different result. The core seems to struggle with the middle part of the burn although no fuel overload occured.



So, what to do? All the latter testruns with the new liner configuration in the riser box were done with a 70% riser port and a 100% end port. In order to check, I changed the riser port to 60% again and ran it on the second day of Christmas, 2 Bft this time. The warming up hill in the first part is still there but the entire burn stayed above 8% of oxygen.



The same burn was repeated on December 27th, 2 Bft again and it showed again the behaviour I was trying to avoid. This burn wasn't a good one, not to the point of smoke from the chimney but it was too close for my liking.



Most burns show this CO hill in one form of another. It seems it is nearly always there during a cold start. The question is now, could I do something in order to mitigate the effect or change to a quicker heating up afterburner? Ehrmm... maybe by shifting the end port to the front of the riser box? I mentioned this idea before but didn't use it, yet. This seems to be the right time to do it and so I did. Here are two pictures of the changed port location, it looks a bit rough around the edges but it's the correct 100% chimney csa opening.





Always a bit tensive, a new step, so I loaded up the firebox with a smaller load, with more air between the pieces than before. Together with the 6 Bft which was going on outside it could overload, without question. And to my surprise, it didn't. The CO hill in the first half remained absent, the O² went a bit too low for my liking but it did cope quite well.



Next step will be: run another test, same configuration and hopefully the same wind circumstances. It might be that the riser port is too narrow now, but that remains to be seen. I might try hardwood now, the two bought nets of oak seems to be dry enough.

[independentenergy]

bad news for me Peter....in my build there isn't enough space for a front port.
If I understand correctly, the problem lies in the fact that the core is slow to heat up?

[peterberg]

Dec 28, 2023 23:01:43 GMT -8 independentenergy said:

bad news for me Peter....in my build there isn't enough space for a front port.
If I understand correctly, the problem lies in the fact that the core is slow to heat up?

For best performance while starting cold, it should heat up somewhat quicker, yes. This disadvantage isn't important when the stove/heater is run every day as a real mass heater.
When space is a problem you could use the top end port configuration in that case.

[peterberg]

Yesterday I did another testrun, not sure whether or not this was the last one for this year. I felt a bit adventurous, the small oak pile next to the heater looked good so I filled it with some fitting logs for this small firebox. Two small softwood planks on top and a handful of tinder plus a barbeque lighter. The layer of fresh charcoal underneath is there intentionally, it provides for better lighting of the lowest logs. The sloppy looking pieces of aluminum tape left and right in the door frame were ripped out early in the burn, this was part of another (failed) test.



The fire came on slow, the start bulb of CO was there once again although not alarmingly high. On the 24 minutes line I fiddled a bit with a piece that was still on top but not really burning well. While the burn was underway and on 30 minutes, I felt the small oak logs weren't as dry as I hoped for. So, I took another one larger piece from the pile and splitted it. The fresh split side brought 22% humidity on my simple moist measuring instrument. Far too wet, but the burn went on nevertheless quite well. Towards the end of the burn the CO went up sky-high, to be expected with damp wood, forming lots of coal. Despite all this, the burn was still within the confinement of the current EU regulations. The Testo filter came out lightish grey, which means there was just a tiny amount of soot formed and exhausted through the chimney. Throughout the burn, no smoke at all from the chimney and not even water vapour. Outside temperature was a little bit over 10 ºC, equivalent to 50 ºF.



The relative ease of burning wet wood while maintaining reasonable burn quality is remarkable, just my opinion.