IR Thermometer 'Snapshot' - Hot Coal Bed...

[karri0n]

Pete:

I can't quite figure that stove from the diagram, but I sure like your old one. I give you credit for working with it and trying to contrapulate a way of increasing efficiency.

 

[Peter B.]

Here are a couple of photos of the firebox and coal bed in question...

Note again that the rough arch in the center is through which all 'products' from the stove must pass before the rest of the baffle (and catalyst) are negotiated.

I wish I had a glass door to see what happens on a fresh fuel load... but I don't.

Flying Blind.

Peter B.

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[Peter B.]

A closer view...

 

[Frostbit]

Bringing the Raytek Raynger ST80 home tonight, it will read to 1400 degrees, so we'll see what we have. Have the wife's birthday dinner to tend to, then the fire, so it will either be late (and we're 4 hours back of east coast time), or tomorrow before you see any post from me after this.

Is a coal bed a coal bed, regardless of fuel makeup, as far as expected temperatures go? I'm burning hardwood pallet scraps, black spruce, and some pine, so its a mix in my stove. Found out last night with the Fluke 62 that the door needs to be opened...the IR wants to read the glass temp, even though I can see the beam in the coals. I knew something was amiss when the reading temp was only 400 plus degrees. So, the open door will make it hard to get an "idle", or no draft, reading on the coal bed.

We'll do what we can!

 

[Peter B.]

Is a coal bed a coal bed, regardless of fuel makeup, as far as expected temperatures go? I'm burning hardwood pallet scraps, black spruce, and some pine, so its a mix in my stove. Found out last night with the Fluke 62 that the door needs to be opened...the IR wants to read the glass temp, even though I can see the beam in the coals. I knew something was amiss when the reading temp was only 400 plus degrees. So, the open door will make it hard to get an "idle", or no draft, reading on the coal bed.

We'll do what we can!

Frostbit:

Thanks for this...

I don't think anymore than a subjective comparison can be made between 'your coal bed' and 'my coal bed'... (which is mostly oak).

But the IR reading would still be of real value to me... whatever you get... whenever the results 'arrive'.

Happy B-Day to your wife.

Thanks for your time.

Peter B.

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[Cowboy Billy]

KarriOn thanks for the second diagram. Definitely looks like what I want to do. I want to quit burning coal but I have to improve the efficenticy of the stove with how far I have to go to get wood.


Very good Peter. I can see how you have yours set up. Thanks! Do you have additional air supply to your secondary burn system? As you know from helping me with my stove you know I have a round oak too.

Billy

 

[Frostbit]

Well, here goes. I established about an 1 1/2" bed of coals, though not over the entire bottom. My F400 primary was at full left, which is "closed". I opened the door with the IR gun in hand, and direct in the glowing coals it was 1150 degrees. In very short order (the door is now open), maybe 15-20 seconds, the temp ran right on past 1200, then 1300. 1350-1370 was prominent for a short while, then I had two over 1400, as the screen went blank. It would have been interesting to see just how high it would climb to, but just not possible with this gun, or with the door open.

That's all I could do, Peter.

 

[karri0n]

Keep in mind that with the door open, most of the air is rushing above the coals and straight up the chim without really blowing on them. With the door closed and the primary open, the air sprays directly on the coals, making them shine with those bright orange/yellow colors. I would guess that they reach 1800 easily. For the most part, the glow color isn't all that dependent on the material, it just happens because the molecules in the product have so much energy that some of it is radiated in the visible spectrum. Technically, everything is always glowing, but it doesn't reach the frequencies that can be seen by the human eye. If you had a far infrared scope, you would be able to see these.

 

[Peter B.]

Well, here goes. I established about an 1 1/2" bed of coals, though not over the entire bottom. My F400 primary was at full left, which is "closed". I opened the door with the IR gun in hand, and direct in the glowing coals it was 1150 degrees. In very short order (the door is now open), maybe 15-20 seconds, the temp ran right on past 1200, then 1300. 1350-1370 was prominent for a short while, then I had two over 1400, as the screen went blank. It would have been interesting to see just how high it would climb to, but just not possible with this gun, or with the door open.

That's all I could do, Peter.

Frostbit:

This is music to my ears... or eyes. For twenty years, I've been in the dark about this... only had 'suspicions'.

My final baffle design (as described) was sort of an act of desperation, because other trials (all involving only upward flow through the stove) had never allowed me to control the rate of burn in the Round Oak. Even with other flow restrictions and a flue damper (I think I even tried two dampers at one point), I could still get runaway fires. So simply improving control was my primary goal... and the low entry point of the baffle seemed to provide that. While I had an idea that the coal bed was 'pretty hot', I've never been sure (before now) that the temperature was sufficient 'on paper' to support secondary combustion.

Though I did (and still) introduce some additional 'overfire' air, I don't think I've ever concentrated enough adequately preheated air to the immediate vicinity of the baffle entry. I'm now going to try to do so. The 'plumbing' will be a bit of a problem (because I don't much want to drill holes in the stove body), but not insurmountable. I can't readily preheat incoming air from the stove's existing draft controls. And I may not be able to try anything new this season (it's going to be double digits below zero here tonight and tomorrow night), but I'll definitely be ready for next year... at the latest.

The two (other) main drawbacks to the current setup are that (of course) a good, hot coalbed has to be built up before any secondary combustion is likely, and the baffle could really use some sort of bypass (reloads can be a bit smoky at times).

And there's some lingering doubt in my mind whether heat transfer from the stove is as effective as it could be, given that the baffle is isolated/insulated from contact with the stove body itself for much of its length.

Again, my original 'R & D' efforts were dictated by the fact that the stove was far from airtight, required vertical wood stacking (and burn pattern), and had absolutely no internal baffling to begin with... the flame (along with all the unburned volatiles) just shot right up the flue. Pretty much the only sort of fire that could be had was 'flat out'... and fast.

Anyways... just thinking out loud...

Having the coal temps bracketed (at least at the low end) is of real use to me for further thought and trials. I will - at the very least - now be pushing coals towards the throat of the baffle on reload... I never bothered before.

Thanks very much (once again) for your time and the 'vicarious' use of the Raytek Raynger. I owe you.

Peter B.

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Cowboy Billy: I think I answered your last question in this post. Good luck with your own Round Oak, but be gentle with it, if it's complete, it's worth something on resale to a restorer.

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[karri0n]

You can probably improve heat transfer and slow the unburnt volatiles down simply by placing the three plates as described in my earlier post, requiring the gases to make 2 180° turns before exiting the flue.


edit: If everything needs to pass through that small spout before it can exit the firebox, then you should have the "compression" part taken care of just fine, and I'm quite certain that area reaches temps required for secondary combustion. You have two of three, now it's just a matter of introducing extra air to that area. I'm not sure if you can actually do this without drilling the stove body, but any air inlet you put directly to the inside of that scoop will be preheated by passing through the firebox. If you want to be even more certain of this, you can put some fins on the exterior of the air tube(exterior, but inside the firebox, hope you follow me on this) to give it even more heat transfer to the air within the tube.

 

[Peter B.]

You can probably improve heat transfer and slow the unburnt volatiles down simply by placing the three plates as described in my earlier post, requiring the gases to make 2 180?° turns before exiting the flue.


edit: If everything needs to pass through that small spout before it can exit the firebox, then you should have the "compression" part taken care of just fine, and I'm quite certain that area reaches temps required for secondary combustion. You have two of three, now it's just a matter of introducing extra air to that area. I'm not sure if you can actually do this without drilling the stove body, but any air inlet you put directly to the inside of that scoop will be preheated by passing through the firebox. If you want to be even more certain of this, you can put some fins on the exterior of the air tube(exterior, but inside the firebox, hope you follow me on this) to give it even more heat transfer to the air within the tube.

karri0n:

While I'm (definitely) interested in alternatives to my setup, I think 'engineering' the three plate idea would pose some problems in my specific situation.

Currently, the lower portion of the baffle runs vertically for about 12-16", then right angles into a circular chamber about 10" in diameter. The exhaust then passes up through a 6" round catalyst with a protective guard over it that forces the flow to the sides of the top chamber... which is actually the cast iron 'cap' of the stove. Then, it's all through another 90* headed up the flue and past/through the damper.

The circular chamber has sort of a flyash 'cyclone' effect and can be vacuumed when necessary. The three plate design would also catch flyash, but would be difficult to clean. And there wouldn't be room for both the catalyst and the three plate addition. At the moment, I tend to rely on the catalyst to clean up the smoke... from the deficiencies of the rest of the system.

Adding additional air to other parts of the baffle (besides the entry point) would likely be beneficial, however. I have a drilled view hole in the top 'cook plate' immediately above the catalyst guard. After a typical burn, most of the guard tends to be white to a light cream... but the area exposed to the air coming from the view hole appears to be even cleaner.

I think you're right though that the 'reside time' in the stove may not be long enough for good heat transfer. During a normal burn, the internal flue temp (12" from the stovetop) runs about 500* when the stove is throwing strong heat. I think that's a little high, and would like to dissipate more heat from the stove rather than sending it up the chimney... but haven't figured out how to manage that yet without a complete redesign.

I'm not saying it ain't plausible or possible... just that I'm not ready yet to toss what I've got and start over again.

Thanks for your suggestions though... I'm open to others.

Peter B.

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[karri0n]

I wasn't saying to trash what you've got, but I understand now that the top isn't open like I initially suspected.


Are you saying you already get extra combustion air to the entry point of the baffle? If so, I'd say it's safe to assume you are probably getting secondary combustion near that air inlet. Where, other than the top hole, does secondary air come in?


With your description of the area near that top hole, it sounds like you are getting secondary combustion in that area as well. It sounds to me like your system is working masterfully.

 

[Cowboy Billy]

Peter I just got a small Mars stove that looks like a Round Oak knock off. It is quite short and the upper tin that the door is in is bad. We are thinking of having a sheet of stainless steel rolled out and welded that is the same dia of the original one. But we were going to make it 12" taller. If you wanted to do that much work you could make one tall enough to put the baffles in and take the original tin and keep it so you have it for your original value.

Billy

 

[Peter B.]

Are you saying you already get extra combustion air to the entry point of the baffle? If so, I'd say it's safe to assume you are probably getting secondary combustion near that air inlet. Where, other than the top hole, does secondary air come in?

Yes, I've got a simple (read: primitive), undersized secondary tube feeding supplemental air near the baffle entry. (You can just barely make out the end of the tube to the left of the baffle entry in the photos I attached above).

But I'm thinking it's not enough... and that my next step will be to add a 'surplus' of well preheated air to the same spot.

I know there is some secondary combustion occurring even from the existing (inadequate) supply, because when all other drafts are closed (and the room is quiet), I can hear a flame ignite periodically from the secondary tube.

Peter B.

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[karri0n]

ok so force the air,increase the temp & exhaust it out the chimney. i wouldnt unless the coalbed was too big.

CZARCAR:

You still ain't 'gittin' it'...

The idea is not to try to burn down the coals, but to burn off the volatiles (from the rest of the wood load) as near as possible to the heat the coals produce.

Peter B.

-----[/quotehttp://extn.msu.montana.edu/Publications/ESCatalog/HOMEPublicCatalogHomelist.asp?start=61
click & read the first link about principles of combustion.

[/quote]


What aren't you getting here? We aren't arguing the point of putting more air over the coals, and we're well aware of the three stages of combustion. The question we're now working on has nothing to do with coals, how much gas they exude, or even their temperature with or without air. We've found that he will have enough heat to initiate secondary combustion, and that you are a troll.

 

[karri0n]

Peter,


I think the best spot actually to feed your secondary combustion air will be to the inside of the cylinder. this will work just like a secondary burn chamber, and will make for a pretty clean install since it won't be sticking into the firebox where you need to put wood. I think that area is hot enough, especially since you seem to be getting secondary combustion at the top of the stove where you drilled the viewing hole, and this is even further from the flames and wood load.

 

[Peter B.]

Peter,


I think the best spot actually to feed your secondary combustion air will be to the inside of the cylinder. this will work just like a secondary burn chamber, and will make for a pretty clean install since it won't be sticking into the firebox where you need to put wood. I think that area is hot enough, especially since you seem to be getting secondary combustion at the top of the stove where you drilled the viewing hole, and this is even further from the flames and wood load.

karri0n:

Still thinking on it all... and Frostbit's IR results are still fresh news to me, so it will be awhile before I make up my mind exactly what to do.

--

For now, I think I'm doing purty good... given the ancient machine I'm working with. I just hope I've got enough 'volatiles' stacked on the back porch and in the back yard to see me through to April... when my new garage (and workshop) should be finished and I can get serious about doing something more with the Round Oak.

Maybe when I can get to it, I'll break down the whole baffle and take photos of the parts, the stove interior (with and without) and post them all here.

Peter B.

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[Peter B.]

Peter I just got a small Mars stove that looks like a Round Oak knock off. It is quite short and the upper tin that the door is in is bad. We are thinking of having a sheet of stainless steel rolled out and welded that is the same dia of the original one. But we were going to make it 12" taller. If you wanted to do that much work you could make one tall enough to put the baffles in and take the original tin and keep it so you have it for your original value.

Billy

Billy:

The sheet steel body of my stove is in pretty good shape yet, and it's solidly riveted to the lower firebox and the loading door frame. I think it's going to stay that way for the time being.

And for another reason too...

The top trim ring that stands about two inches away from the body of the stove is almost perfect 'butt height' for me. I can back up right next to the stove on cold days and 'bounce' on and off the hot trim ring... and think deep thoughts.

Couldn't do that if the same ring was at shoulder height... just wouldn't be the same.

Peter B.

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[Peter B.]

ok so force the air,increase the temp & exhaust it out the chimney. i wouldnt unless the coalbed was too big.

CZARCAR:

You still ain't 'gittin' it'...

The idea is not to try to burn down the coals, but to burn off the volatiles (from the rest of the wood load) as near as possible to the heat the coals produce.

Peter B.

-----[/quotehttp://extn.msu.montana.edu/Publications/ESCatalog/HOMEPublicCatalogHomelist.asp?start=61
click & read the first link about principles of combustion.

CZARCAR:

Thanks... I already had that article on my computer, it's a good one and I have studied on it... but it didn't answer the question I posed here.

By now, I flatter myself that I know the ABC's of wood burning... or at least the bare basics, anyway.

Peter B.

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[Cowboy Billy]

Billy:

The sheet steel body of my stove is in pretty good shape yet, and it's solidly riveted to the lower firebox and the loading door frame. I think it's going to stay that way for the time being.

And for another reason too...

The top trim ring that stands about two inches away from the body of the stove is almost perfect 'butt height' for me. I can back up right next to the stove on cold days and 'bounce' on and off the hot trim ring... and think deep thoughts.

Couldn't do that if the same ring was at shoulder height... just wouldn't be the same.

Peter B.

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Amen Peter that sure is a satifing feeling!!

Billy

 

[Peter B.]

An Epilogue...

Quoting myself:

"I will - at the very least - now be pushing coals towards the throat of the baffle on reload… I never bothered before."

--

The following observation is likely premature, and I'll probably be back to eat my words before the day is out, but...

I'm feeling like a supreme bonehead at the moment. After twenty years with my (much advertised) stove modifications in place, it would appear that - in all that time - I never learned how to put them to best use.

Yesterday, I began doing just what I 'threatened' above... on reloads, I now make a pile of hot coals right in front of the baffle entry, then load the stove as I usually do... haphazardly... whatever's at hand that fits.

That single change in my burn habits appears to have substantially changed how the stove behaves under 'need heat' situations... and I'm staying warmer than I can remember in double digit below zero temps.

For want of a better description, this is shaping up to be (very decidedly) a "Doh" moment for me.

Thanks for this Forum, and thanks to all who contributed to this thread.

Peter B.

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