Temp of Wood Flames?

[svk]

I’m in a discussion on a different topic site about the temperature of flames from a wood fire. Guy is saying all wood species burns within 6 degrees of each other because he saw a study that compared two species that were 6 degrees apart. I disagree considering some species hardly burn on their own while others like tamarack will burn through a barrel stove if you aren’t careful.

Do you guys have anything to add to this discussion?

 

[Drptrch]

https://www.arboristsite.com/community/threads/btus-per-pound.141280/

https://chimneysweeponline.com/howood.htm


http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/


Erik

 

[Deleted member 117362]

I’m in a discussion on a different topic site about the temperature of flames from a wood fire. Guy is saying all wood species burns within 6 degrees of each other because he saw a study that compared two species that were 6 degrees apart. I disagree considering some species hardly burn on their own while others like tamarack will burn through a barrel stove if you aren’t careful.

Do you guys have anything to add to this discussion?

Not sure this will completely answer your question:
Flame Temperatures in Wood Burning Fires: Hardwood vs. Softwood
Faith C. Myers, Big Walnut High School

The purpose of this experiment was to determine if hardwood (oak) or softwood (poplar and pine) produce more thermal energy by measuring maximum flame temperatures and burn times, and determining relative areas under temperature-time curves. Research and Myers’ previous experimentation led to the hypothesis: hardwood will produce the highest amount of thermal energy based on flame temperatures. The hypothesis was tested by evaluating maximum flame temperatures generated. Eight pieces of wood (each 0.6 cm long and 3.2 cm in diameter) were dipped into kerosene and placed onto shredded paper (25g) in a fireplace. Kerosene (5 ml) was poured onto the wood and the paper was ignited with a match. After burn-off of kerosene and paper (1 minute), maximum flame temperatures (°C) were recorded at 1s intervals until flame-out for each wood type using an infrared (IR) thermometer - and the maximum temperature for each trial recorded. Ten trials were performed for each wood type and maximum temperatures were averaged and standard deviations calculated. The mean maximum flame temperatures were: pine 504.8°C, poplar 501.2°C, and oak 499.5°C. This result did not support the hypothesis, as the difference in maximum flame temperatures was statistically insignificant. The mean burn time (minutes) was: oak 12.2, pine 7.4, and poplar 7.2, supporting the hypothesis. The mean relative area under the temperature-time curve was: oak 258, pine 182, and poplar 175, supporting the hypothesis. Therefore, the hypothesis that hardwood would produce more thermal energy than softwoods was supported by two of three thermal energy indicators.

 

[svk]

Not sure this will completely answer your question:
Flame Temperatures in Wood Burning Fires: Hardwood vs. Softwood
Faith C. Myers, Big Walnut High School

The purpose of this experiment was to determine if hardwood (oak) or softwood (poplar and pine) produce more thermal energy by measuring maximum flame temperatures and burn times, and determining relative areas under temperature-time curves. Research and Myers’ previous experimentation led to the hypothesis: hardwood will produce the highest amount of thermal energy based on flame temperatures. The hypothesis was tested by evaluating maximum flame temperatures generated. Eight pieces of wood (each 0.6 cm long and 3.2 cm in diameter) were dipped into kerosene and placed onto shredded paper (25g) in a fireplace. Kerosene (5 ml) was poured onto the wood and the paper was ignited with a match. After burn-off of kerosene and paper (1 minute), maximum flame temperatures (°C) were recorded at 1s intervals until flame-out for each wood type using an infrared (IR) thermometer - and the maximum temperature for each trial recorded. Ten trials were performed for each wood type and maximum temperatures were averaged and standard deviations calculated. The mean maximum flame temperatures were: pine 504.8°C, poplar 501.2°C, and oak 499.5°C. This result did not support the hypothesis, as the difference in maximum flame temperatures was statistically insignificant. The mean burn time (minutes) was: oak 12.2, pine 7.4, and poplar 7.2, supporting the hypothesis. The mean relative area under the temperature-time curve was: oak 258, pine 182, and poplar 175, supporting the hypothesis. Therefore, the hypothesis that hardwood would produce more thermal energy than softwoods was supported by two of three thermal energy indicators.

I’m thinking this is the study he saw

 

[svk]

https://www.arboristsite.com/community/threads/btus-per-pound.141280/

https://chimneysweeponline.com/howood.htm


http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/


Erik

I understand the BTU chart ie “total output” of wood very well. What I’m looking at here is temp while burning.

 

[Deleted member 117362]

Learn something everyday.

I understand the BTU chart ie “total output” of wood very well. What I’m looking at here is temp while burning.

Must just have to add forced air to increase temps.

 

[M.R.]

Higher temps.....
Wood fired Blacksmith forges.

 

[Ted Jenkins]

Based upon my experience NO. The charts are not correct at all in terms of the temperatures for a typical wood stove. The tests look good for what was tested, but in real world facts no. There are a few factors that effect the internal temperatures of a stove that do not just relate to the type of wood being used. Oak has more BTU's than Cedar, but Cedar can burn very hot. I think the bottom line here is how fast can the wood be consumed. I use a furnace to melt Aluminum because I get so much of it and need to make ingots out of the scrap I have. Oak does not work as well as Pine to get the furnace cherry red. Does that mean that Pine is better than Oak for heat production? If you add compressed air to a burn process now every thing changes. I can approach 1800 F but not past it. Aluminum is long since a puddle that starts to oxidize. Thanks

 

[Streblerm]

Here’s my thoughts on the topic FWIW. BTU is the measure of energy contained in the wood but not the actual temperature of the flame. I think we can agree that different wood species contain about the same BTU per pound. This sounds like it supports your friend’s theory but there are other important aspects to BTU. One is the/H being time and the fact that fire literally and figuratively doesn’t burn in a vacuum.

The temperature of the flame is dependent on more than just the density of the fuel. Fire needs fuel(wood) oxygen, and an ignition source. Increasing oxygen to the fire will increase flame temperature and decrease time. Somebody mentioned a forge, hot enough to melt steel while a campfire will not. Moisture content plays a huge role as well. My stove chock full of damp oak struggles to reach 400* while three little pieces of dried maple will have it at 650* in a short time. Surface area is another big factor. A pile of small splits will produce a hotter flame than one big log.

So, in a lab situation with an equal weight of wood with equal moisture content and surface area from different species given an equal amount of air the flame temperature might be about the same. Point to your friend. If he is trying to claim that all wood fires are within 6 degrees of each other, well, there are just too many variables involved in a fire. My experience tells me that wood fires can burn at drastically different temperatures depending on those other variables.

 

[Del_]

I think the confusion comes from people thinking that more flame equals higher flame temperature.

It doesn't.

Materials burn at certain temperatures. The more of a given material on fire the higher the total heat output of the fire but that does not necessarily relate a higher flame temperature.

 

[rarefish383]

My old cat stove could be choked down to where the stove temp was about 400* and still burn clean and efficient. My new non cat stove burns hotter. But if I use an IR on the flames dancing in both stoves , are the flames the same temp? I can see where the flames themselves have little to do with the stove temp, all those other factors influence, space being heated, amount of fuel in that space, oxygen, material of construction. If one stove is choked down to 400* and the other runs wild to 900* are the flames in both still around 500*?

 

[rarefish383]

Del, you type faster than me. Trying to say the same thing, same point, Joe.

 

[svk]

Right, what I’m getting at is something like Tamarack burns really hot versus some species barely can keep themselves burning without additional fuel. There has to be more than 6 degrees on the spectrum.

 

[grizz55chev]

Real world experience tells me that wood like madrone and eucalyptus burn hot and clean, less ash but don’t last as long as oak. Pine burns hot and fast, lots of ash, I use mostly madrone with a mixture of oak for longer duration.

 

[rarefish383]

What I'm trying to wrap my mind around is, yes, different woods might make a hotter fire, but, does that mean the flame its self is hotter? The flame is a visual indicator that the wood is burning. Without adding forced oxygen, or other gasses, can you push the temp of the flame past a certain point? I think we would need to do tests with the IR or color of flame analisis. Aren't different temps represented by different colors, red, yellow, orange? Now I'm going to have to pester my physicist son.

 

[grizz55chev]

I believe white is an indication of the hottest.

 

[Wood Doctor]

Right, what I’m getting at is something like Tamarack burns really hot versus some species barely can keep themselves burning without additional fuel. There has to be more than 6 degrees on the spectrum.

There is one theory that I have that mixed hardwoods work better as a team making a fire than one species burning by itself. Some light faster and others burn longer. Put them together and you usually come out ahead. However, I have never seen a study with findings that support this theory.

 

[rarefish383]

But the original question was the temperature of the "FLAME", not the fire.. If I put one piece of Oak in my stove and it burns to ashes, it won't even get the stove hot, but the "FLAME" will still have reached a temp of 500*, per the statement above. If I pack my stove full of Oak, and leave the draft open, it will get to 900*, but how hot is the actual flame, still 500* per statement above. As stated above, the "FLAMES" of any species of wood only vary a few *. It doesn't matter what combination of wood makes the hottest or longest fire. How hot does the "FLAME" actually get? Joe.

 

[Wood Doctor]

But the original question was the temperature of the "FLAME", not the fire.. If I put one piece of Oak in my stove and it burns to ashes, it won't even get the stove hot, but the "FLAME" will still have reached a temp of 500*, per the statement above. If I pack my stove full of Oak, and leave the draft open, it will get to 900*, but how hot is the actual flame, still 500* per statement above. As stated above, the "FLAMES" of any species of wood only vary a few *. It doesn't matter what combination of wood makes the hottest or longest fire. How hot does the "FLAME" actually get? Joe.

That's correct and exactly why all species of wood produce about the same heat per pound. Cottonwood heat per pound is about the same as oak per pound. It just takes more volume of cottonwood to equal the same weight as oak.

I recall an older guy telling me years ago that if I really wanted to make a cold cabin warmer the fastest, forget trying to burn oak in the stove. Load the stove with cottonwood to get the fire going. Add oak later.

We rate wood usually in BTU/Lb, but maybe we should look more carefully at BTU/Lb/Hr. Throw time into the equation now and then. Just MHO.

 

[Ted Jenkins]

What I'm trying to wrap my mind around is, yes, different woods might make a hotter fire, but, does that mean the flame its self is hotter? The flame is a visual indicator that the wood is burning. Without adding forced oxygen, or other gasses, can you push the temp of the flame past a certain point? I think we would need to do tests with the IR or color of flame analisis. Aren't different temps represented by different colors, red, yellow, orange? Now I'm going to have to pester my physicist son.

I like to put Oak into my forge because it last longer, but adding a blower to any wood makes the temperature jump to at least 1500 F. When the flames are no longer present is when the temperature is the hottest. So flame does not indicate much, but maybe a good yellow flame is at the similar temperature. Thanks