|
Post by peterberg on Mar 20, 2019 1:09:19 GMT -8
From what I have seen as far as lack of creosote in these heaters, I'm betting any HC's not fully broken down are going to be in the C4 range. I'm not familiar which this C4 as a product of combustion. Google comes up with a French car, a New Zealand television channel and a plastic explosive among other things, I presume neither of these are what you meant.
|
|
|
Post by esbjornaneer on Mar 20, 2019 1:58:04 GMT -8
|
|
|
Post by gadget on Mar 20, 2019 6:15:25 GMT -8
From what I have seen as far as lack of creosote in these heaters, I'm betting any HC's not fully broken down are going to be in the C4 range. I'm not familiar which this C4 as a product of combustion. Google comes up with a French car, a New Zealand television channel and a plastic explosive among other things, I presume neither of these are what you meant. C4 is just a reference slang for the simple hydrocarbon group with 4 carbon atoms or less. Methane being the primary (CH4) for wood gases. Methane, Ethane, Propane and Butane( I had to look that list up) There is not allot of info on the chemistry of wood combustion. I would bet there is also lots of H and C in the mix along with unsaturated hydrocarbons. I am not an expert in this area but I do tinker on the subject.
|
|
|
Post by independentenergy on Mar 20, 2019 6:49:15 GMT -8
Peter this point, given the temperatures at stake, wouldn't it be wiser to build the black oven after the second chamber? I dare not imagine a core scaled to 150mm as far as it can go
|
|
|
Post by peterberg on Mar 20, 2019 7:46:42 GMT -8
C4 is just a reference slang for the simple hydrocarbon group with 4 carbon atoms or less. Methane being the primary (CH4) for wood gases. Methane, Ethane, Propane and Butane( I had to look that list up). Ah, now I see what you mean. My knowledge of combustion chemistry is even more sketchy as yours, I have to admit.
|
|
|
Post by peterberg on Mar 20, 2019 7:50:35 GMT -8
Thanks for the offer, this might be an idea, haven't seen it for sale before. I'll investigate and come back to you if and when necessary.
|
|
|
Post by peterberg on Mar 20, 2019 8:02:39 GMT -8
Peter this point, given the temperatures at stake, wouldn't it be wiser to build the black oven after the second chamber? I dare not imagine a core scaled to 150mm as far as it can go There has been a time I couldn't imagine a 200 mm batch box system. In fact, it turned out it wasn't that much different, larger systems tend to be more stable combustion processors instead. The first upscaled 200 mm system scared me by the sheer violence of the burn, that's true, but one gets used to it very quickly. So I'd love to see a DSR2 scaled up to, say, 250 mm? (Ten inch in old money.)
|
|
|
Post by Vortex on Mar 27, 2019 11:20:10 GMT -8
I don't know who at first mentioned making the exhaust port smaller than system csa, this might be Trevor or Brian. The argument was providing back pressure, and for all I know that would be the same effect as my knowledgeable guy said it would. Thanks guys, for providing an alternative route of thinking. Another thought: what would happen when the top of a normal vertical riser is restricted slightly? Peter, regarding the back pressure. I recently bought a new chimney cowl, as I would occasionally get water dripping down the inside of the pipe in windy wet weather. The cap of the old cowl is quite high above the top of the stove pipe, so I thought a normal lower one would solve it. When I lit the stove the fire burned exactly the same as usual. Gas flow rate seemed the same as normal, not sluggish at all like I would expect if there was too much back pressure, but mid burn the afterburner window gradually went black, when I went outside the chimney was smoking. I removed the new cowl and within a few minutes the smoke disappeared, when I got back into the house the afterbuner glass had burned clean again. I tried this 2 more times and got the same results. I was really surprised how much difference a slight increase in back pressure made. There seems to be a Goldilocks zone.
|
|
|
Post by peterberg on Mar 28, 2019 0:50:31 GMT -8
Yes, there is. Gasifying is a critical process, all circumstances need to be within narrow tolerances. You might get away with that lower chimney cowl when there's stronger draft, i.e. higher stack temperature.
|
|
|
Post by peterberg on Apr 2, 2019 3:31:57 GMT -8
Actually, what I've seen coming by is hard to describe and my interpretation may be way off but I'll try. I switched to soft wood some weeks ago since the results weren't what I would like to see. But the burning characteristics more or less remained the same. Too quick development of the fire and a steep and low dip in the O² line, half of the time accompanied by a peak in the CO line. Sometimes within average specs and sometimes not. The trip wires at the ceiling and side walls seemed to work but not at every instance.
An evening of printing diagrams and comparing numbers told me the overhanging brick and the trip wires influenced the burn in a different way while both seemed to have an overlap in function. The overhang tend to shift the dip in O² (height of the burn) to later in the burn, while the trip wires seemed to confine the flames to the back of the oven to some extend. And the wires were better to keep the CO down.
I chiseled the wires out, repaired the walls and re-introduced the overhang right where the ceiling trip wire used to be. The brick hanging down one inch, not more. Results were nice but not consistent, every third run the CO went haywire. So I shifted the brick to halfway in the depth of the oven/expansion tunnel, still hanging down one inch. This worked much better, top of the burn was shifted to around halfway in the diagram. And, just as important, the flames in the oven stayed in the back of the oven for quite a bit longer.
That last configuration was tested seven times up till now, using the same fuel. Two logs of 3.5" square at the bottom and three pieces of 1.75"x3.5", plus a handful of kindling on top and a smaller piece on top of that. None of the loads were stacked higher than the top of the port, kindling included. Regrettably, that same fuel is running out now so I need to switch to some other type. There's some oak and beech lying around, enough for two runs. Tonight I am going to do one run with that and see what happens.
And oh yes, every time a gust of wind came by the flames roared fiercely but seemingly all of the afterburning happened in the riser stub, i.e. no flames in the oven for the duration of the gust. I figured a slightly larger primary air supply would be better, so five of the seven runs were done like that. With commendable results, I have to say. I'll report back tomorrow.
Edit: Another indication of the last series of tests' quality is the colour of the Testo probe's white filters. I use those filters between 8 and 12 times, letting it dry thoroughly between tests until it's too dark to see a colour difference. The last run I used a pristine filter which is almost dry now and is coloured very faintly grey. This is excellent, it means the black organic carbon (and dangerous) component in the fine fly dust is almost completely absent.
|
|
|
Post by peterberg on Apr 3, 2019 7:45:48 GMT -8
Report of the progress so far. Burning small planks using the configuration described above went well, the one inch overhang of that brick seems to do the trick. Here's how it was loaded, above the fuel there was just enough space to access the barbecue lighter with a match. Weight of the fuel 2.5 kg. And this is the resulting diagram. For who's interested: averages O² 13.3%, eff. 89.0%, CO 674 ppm, stack 119.3 ºC. OK, so small to medium fuel isn't a problem anymore. Bigger pieces of lark being the next test. Loaded like this, all four of these tests alike, weight of the fuel 2.0 kg. Results of these four are more or less the same, all were done with the enlarged primary air opening. Averages: O² 12.7%, eff. 89.7%, CO 502 ppm, stack 126.0 ºC. Two tests with bigger pieces of oak, weight of fuel 3.0 kg, the first run 5 pieces much like this picture. Once it came up to temperature I closed the make-shift door to the newly found csa and let it go. Averages: O² 12.8%, eff. 87.4%, CO 683 ppm, stack 138.0 ºC. Fuel was quite dry, 17%. This morning I ran another test with oak and beech which was not as dry: 21%. Also 3.0 kg, but in four pieces this time. Development was quite slow, oxygen didn't get very low but there were no negative implications, much to my relief. This is a significant factor, most heaters aren't that tolerant to moist fuel. Averages: O² 13.8%, eff. 86.2%, CO 717 ppm, stack 142 ºC. All runs were started from completely cold although warming up of the insulative firebox and expansion box is quick. Not always an advantage, it could also be too quick. The only obvious difference about the last two runs is the higher CO level at the end, averages are well within specs of the EU regulations due for 2022. I am very exited about getting this far. It took a lot of time, frequently changing and a lot of fuel but here we are. Next goal will be building a prototype out of hard firebrick and test this. And fabricating an adequate door and decent air inlet. Not my favourite passtime but a man need to do what need to be done, there's no metal fabricator near me who would be willing to do it for free...
|
|
|
Post by esbjornaneer on Apr 3, 2019 7:53:15 GMT -8
My memory tells me that you only used the rope at the back of the oven (after the riser)... As it made such a difference moving the brick to half way into the oven, what effect would it have to put the rope there instead? The other thing I have been thinking about is, what the effect of letting the gasses leave the oven in the side wall rather than the roof would be, and if that were done what the difference would be if the exit hole extended to the top of the oven or only to an inch below ceiling (with or without a rope trip wire).
Edit: This was started before your last post, seems these comments are not needed by the test results with the brick. Great work Peter!
2.9.1.0
|
|
|
Post by peterberg on Apr 3, 2019 9:37:43 GMT -8
There's one effect caused by the overhanging brick which isn't the same with any of the trip wire tests. The flames in the oven are almost exclusively confined to the back. The trip wires did a good job to break up the stream but it didn't do the confinement thing.
Moreover, uptil now I ran 9 tests in this configuration and those are all in the "very good" department. More test runs will follow, using even smaller fuel to see whether or not it is able to cope. The complete rebuild in firebrick and fabricating a door will follow after.
|
|
|
Post by peterberg on Apr 3, 2019 11:42:10 GMT -8
OK, test number 10 is just done. Two medium sized pieces and a lot of smaller stuff. In any other configuration to date this would lead to a peak in CO, large or small. Not so with this one, a mere wobble, the only thing is that the duration of the burn is limited due to the rather low weight (2.0 kg) of this batch. Averages: O² 11.7%, eff. 89.2%, CO 628 ppm, stack 130.6 ºC. Tomorrow I'll try my hand on small softwood, hopefully all will be within specs.
|
|
Piet
New Member
Posts: 23
|
Post by Piet on Apr 4, 2019 4:50:18 GMT -8
Super exciting Peter!! Once again thanks for all the pioneering.
|
|