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

I asked a similar question last year but didn't get what I thought was a 'definitive' answer.

I'm curious what the temperatures in the immediate vicinity of an 'idling' (wood) coal bed and a 'raging' coal bed are. That is, a coal bed without a draft directed on it, and a coal bed with a strong draft on it or through it.

I wonder if someone with an IR thermometer would be kind enough to post results from one or both coal bed conditions.

(If there are any replies, I'll explain the rationale for the question later in the thread... or in a new one. I don't want to confuse the issue for the moment.)

Thanks Very Much.

Peter B.

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If no one minds too much, I'll keep bumping this post through the day.

It would be really helpful to get multiple responses and a usable range of temperatures.

Thanks Again.

Peter B.

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Thanks for trying Jags...

What's the upper limit for your IR?

(Sooner or later I'll get my own IR, but the question recurred today, and I'd love to have an answer.)

Peter B.

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karriOn:

Thanks for the chart... I wish I knew if it was directly correlatable to coal temps, but at least it provides a relative guide.

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CZARCAR:

Yes, you've missed the point of my question, but thanks for your comments.

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Still hoping someone with a big buck, high temp IR thermometer can nail the coal bed temps down a little closer.

Peter B.

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Okay, okay... but it's likely to be a rather boring anti-climax, I'm afraid.

I've mentioned in multiple other threads that I'd internally modified my antique stove to what I believe is an improved 'state' - in terms of efficiency, burn time and emissions reduction.

The stove was originally designed to burn wood stacked vertically, not horizontally (as in most EPA stoves). This makes for both different burn characteristics and requires a different approach to any modifications hoped to improve on efficiency.

Among the mods I made were these: I lined the lower (cast iron) firebox with firebrick splits, I replaced the original (under fire) grate (to prevent its being damaged by high heat) and substituted a 'sacrificial' grate (that I could safely abuse in the process of my experiments).

I installed a rather elaborate baffle which includes a length of rectangular box steel with an angle cut that opens about 6-8 inches above the firebox floor. *ALL* pyrogas, O2 and other combustion 'constituents' must pass fairly close to the coal bed before entering the baffle... rather than simply rising straight up and out the top flue outlet of the original stove.

THE WHOLE POINT BEING: If the temperature in the immediate vicinity of the coals is 1100* or better, then secondary combustion can occur in that baffle entry 'region' of the firebox with additional introduced preheated air.

If not, I'm whistling in the dark, as it were...

So, knowing what temperatures prevail near the coals is of significant interest to me.

Peter B.

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KeithO said:

Peter

Carbon Ignites at 600C or 1112F. So burning coals have to be at least this temperature. In fact, to be self sustaining the temperature has to be higher. The only concern I have with grasping your concept is that secondary combustion still requires air. To burn wood efficiently (as opposed to as fast as possible) the coal bed must receive limited air, cook the fuel supply to release volatiles, and then these volatiles need to be combusted in a (preferably) isolated space, where they can release heat without spurring more and more rapid combustion of both the coal bed and the wood supply above it. Without physically separating the secondary combustion from the "charring", it is almost impossible to have a long burn. Without adding secondary air (the volatiles are in fact an oxygen starved fuel mixture) you will not get the volatiles to burn clean.

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With respect to your last point, indeed, I am adding (some) secondary air at a point where the temperatures are (apparently) sufficient for burning (some) volatiles.

And again *all* the extant volatiles in the stove must pass through this very hot region before entering the baffle (where the resultant mix is then forced through two right angles and a catalyst before it can leave the stove proper and enter the flue).

My original question was (pointed toward) whether there was an adequate temperature to promote secondary combustion near the coal bed. I'm inclined to think there is, and I'm not sure - provided the whole system is designed around the concept - whether an isolated area is really necessary.

I intend to provide a more generous, better heated secondary air system next season... but thought I'd retest my theory here.

Peter B.

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Frostbit said:

I'll throw my Fluke 62 Mini on mine tonight when I get home, though it only reads to 932 degrees max. Tomorrow I'll bring home the company unit, I believe it will read up to 2K.

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Hey Frostbit...

Both tests would be *really* appreciated... hope you'll post the results when you can.

A semi-conclusive low/high range would be of enormous help to my thinking...

Even if I ain't out to save any world but my own.

Thanks much, and thanks to others so far who've replied.

Peter B.

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Cowboy Billy:

I wish I could draw worth a dam so I could post something that might better explain what I've done... but I can't... and the photos I've taken so far (frankly) aren't that great either. Sorry. Maybe I'll try again for some decent pics, but...

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Edit:

Here's a (bad) composite shot of the lower baffle entry. The 3/16" box steel has (over twenty years) been 'burned' to the arch in the center of the pic. It does get hot there. To the left is the (very primitive, and undersized) secondary supply I'm currently using.

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karriOn:

Thanks for the diagrams... clearly there are plenty of ways to 'skin the cat'. Here's a cutaway of a prototype stove I admire that approaches true gasification... with the exhaust being 'naturally' drawn down into a secondary combustion area before leaving the stove. I'm not familiar with the construction details of the other downdraft stoves out there, but hearing how much trouble people have keeping them running properly, I wonder if the problems with such designs can ever be ironed out.

I stopped short of trying to pull the volatiles directly *through* the coals, but I'm convinced if there was a practical way to do that (and enough heated air supplied), it would result in a very clean burn.

The modifications to my own stove I described are already in place and have actually been in use for about twenty years. Mostly, they've served me pretty well, but this winter I got to thinking (again) how I might make effective improvements to the whole. I've made up a list for next year... I can't take the stove out of use for very long to make changes of any note.

A better secondary air system is high on the list, along with a fresh catalyst.

Though the stove is always 'in focus' during the cold season, I'd (almost) forgotten how much fun it is 'speculating' about different ways and means to burn wood. I have always enjoyed making old things work a little better, a little longer rather than running out to buy the latest and greatest... but the flip side is that I have a lot of respect for the engineering that goes into EPA stoves... and sooner or later, I'll likely buy one.

Just the same, the truth is, I think I'd rather have an unlimited supply of different pre-EPA stoves to play with... and test various methods of taming the 'dragons'.

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Thanks to all for posting their results and comments... I know already (now) that the coal bed temps are 'in the neighborhood' of secondary combustion requirements... which is useful in itself, but I'm still hoping Frostbit will get back with results from the 2K IR thermometer this evening...

Peter B.

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CZARCAR said:

karri0n said:

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

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Click to expand...

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.

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