Discussion of "Primary" & Secondary" burn.

[bogydave]

From my short time on the site I've read lots of terms that I was not familiar with.
2 that got me reading more was "Primary" & "secondary" burn. (several others but some in other topic areas)
It may be a good "sticky" to have a place where members & visitors can go to get a
good definition of "Heart" terms. Discuss a term for input, the poll for the best easy to understand explanation
& post that one in a section "Hearth: "definition of terms used on this site". with some slang or abbreviations & acronyms references.
Or is this already here & I haven't found it yet?

To start with, could we get an explain primary & secondary burn. (too much for one discussions? each term separately?)

Is a cat needed?
Is primary burn when the flame is yellow & looks like it's coming off the wood? More smoke? How to move to the next stage of burning.
Is secondary burn when the flame dances in the stove, bright white, blue , red with no visible smoke.
I notice dancing flames just below the cat, & seems to be directly effected by the amount of air going into
the stove. IE: if too much air, yellow & smokey but too little & smoldering smoke, if just right the flames dance & are
bright & different colors & the stove puts out good heat with very little or no smoke.

Is secondary bur what I should try to achieve? Is it the most efficient burn?
How or what the best way to explain how to achieve a good secondary burn? Dry wood, hot coals, air mixture, atmospheric pressure variances.

 

[Pagey]

My understanding is that primary combustion is when the wood fibers themselves catch fire and burn. Secondary combustion is when the gases released from the burning wood (i.e., the gases released from primary combustion) combust and burn. So, when a fire starts up, you have primary as the wood itself catches and takes off. It doesn't have anything to do with the color of the flame, you don't have to have a catalytic stove only, etc.

 

[Wood Duck]

I'll take a shot at an answer, but instead of my guess I bet you could look it up somewhere. The Chimney Sweep online site probaby has pages about it if you can't find anything here.

I think primary burn is the burn created by the primary air supply, and is the type of burn you'd get in a campfire. Primary burn is the wood burning, and the flames are located at or near the wood in the stove. Any old wood stove or fire pit can create primary burn, which burns part of the wood but gives off gases and smoke which could burn under the right conditions. Modern EPA stoves are equipped with either a secondary air supply (tubes) or a catalytic combustor to create the right conditions for secondary burn of gases and smoke. With a non-cat stove the secondary burn is visible, with a catalytic stove I think the secondary burn is enclosed within the catalyst. In either case, most or all of the gases and smoke are supposed to burn up, giving exta heat from the wood and reducing the emissions and creosote in the chimney.

 

[maxed_out]

Wood ducks reply is +1. If you want to see it go to youtube and do a search for "secondary burn", "efficient burn", etc. Theres many videos that show primary and secondary burn.

 

[caber]

When you see it, you know it. Kinda looks like flames coming out of nowhere.

 

[begreen]

Here's a shot of our Castine's secondaries burning. Note in the second part of the video that the wood looks like it's barely burning. The fuel is outgassing like crazy and the secondary burn is spectacular.

http://www.youtube.com/watch?v=lR98Z4zvX8k

 

[funnyfingers]

I believe technically the wood fibers never burn at least not with a flame. Whenever you see the flames, it is always volatile gases, soft of like the flame off of a wick is the gas of the wax and not the wick itself. The dancing flames are basically the same but the box has reached a higher temperature and those gases are no longer escaping unburned.

The burning wood fibers burn as coals.

 

[bogydave]

Primary burn is a camp fire type fire, lots (unlimited) air. Still the gases burning but gases, temperature & air combine at the right conditions just above the wood surface.
Is that close?

Secondary burn is tougher fro me to get a handle on. The wood is off gassing but the conditions for flame are met elsewhere inside the stove?
Is it hotter? More efficient?

 

[Peter B.]

Here is a link to a pretty good (quasi-technical) discussion of wood combustion:

http://msuextension.org/publications/HomeHealthandFamily/MT198405HR.pdf

Peter B.

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[bogydave]

Here is a link to a pretty good (quasi-technical) discussion of wood combustion:

http://msuextension.org/publications/HomeHealthandFamily/MT198405HR.pdf

Peter B.

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Good link
Thanks

 

[madrone]

Primary burn is a camp fire type fire, lots (unlimited) air. Still the gases burning but gases, temperature & air combine at the right conditions just above the wood surface.
Is that close?

Secondary burn is tougher fro me to get a handle on. The wood is off gassing but the conditions for flame are met elsewhere inside the stove?
Is it hotter? More efficient?

Secondary combustion occurs at a higher temperature. That's the reason for the firebrick and preheated air tubes in a non-cat stove, to increase the temperature and provide air to the upper part of the stove under the baffle, where the gases are. Secondary combustion can occur in a pre-EPA stove if it's running hot enough, but generally a lot of that heat will end up going up the flue. EPA stoves are designed to achieve the temperatures where secondary combustion occur consistently, and without so much incoming air, so the net effect is more heat produced from the same amount of wood. Otherwise, either there is no secondary combustion and the gases just go up the flue unburned, or they are burned, but the draft is massive and just pulls all the heat away. In a catalytic stove, the catalyst reacts with the unburned fuel in the smoke, so most of the secondary combustion is occurring there.

I think.

 

[dave11]

Here's a shot of our Castine's secondaries burning. Note in the second part of the video that the wood looks like it's barely burning. The fuel is outgassing like crazy and the secondary burn is spectacular.

http://www.youtube.com/watch?v=lR98Z4zvX8k

I hope I'm not hijacking the thread, but while we're talking about secondary combustion, I need to ask my last "burning" question about it:

BeGreen--I've watched your video many times, but I'm still wondering if that clip is typical of your stove while "cruising?" That is, can you leave it burning with mainly secondary air, and still maintain the temp for a long period of time (say, for an hour)?

I can get to the same point with my 30NC, but if I leave it like that, the temp gradually falls, and secondary combustion stops. I have yet to figure out if that's normal.

 

[bogydave]

Here is a link to a pretty good (quasi-technical) discussion of wood combustion:

http://msuextension.org/publications/HomeHealthandFamily/MT198405HR.pdf

Peter B.

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Now I have stage 3 burn to put in the brain & rattle around.
Thanks again.

 

[Mad Tom]

Here's a shot of our Castine's secondaries burning. Note in the second part of the video that the wood looks like it's barely burning. The fuel is outgassing like crazy and the secondary burn is spectacular.

http://www.youtube.com/watch?v=lR98Z4zvX8k

. Awesome video!. Being new to the Jotul family, I think it is unfair of you showing that video without telling us your methodology. Kind of wood, how long seasoned and your process in getting to that point. How long will it burn like that?. Give us new epa guys a fighting chance!. . How I long for my old Portland foundry Atlantic.

 

[begreen]

We no longer have the Castine. The video was shot while I was testing compressed logs. Yes, it continued that way without touching the air for a nice spell. The original thread is here:
https://www.hearth.com/econtent/index.php/forums/viewthread/6247/

The show is not as spectacular with the T6 due to the different secondary configuration. However, it will go for a longer time in the T6 because there is a lot more fuel to offgas.