moof Posted January 21, 2008 Posted January 21, 2008 Sorry if this is in the incorrect section.My question is, why do charcoals from different woods have different burn rates? What substance or lack of substance causes them to burn fast or slow?
Frozentech Posted January 21, 2008 Posted January 21, 2008 Sorry if this is in the incorrect section.My question is, why do charcoals from different woods have different burn rates? What substance or lack of substance causes them to burn fast or slow? It's actually not a very well understood phenomenon. Society switched to smokeless powder before the invention of modern analytical equipment, and it there was no money in researching BP any longer. Most sources say it's due to the mix of organics left in the charcoal after the lignins and cellulose are pyrolized. Modern pyro's have never done any better than our forefathers did just by empirical research and a thousand years of trying different things.
mormanman Posted January 21, 2008 Posted January 21, 2008 Its just a guess, but it might also have to do with the way it was grown. Take for instance pine and balsa. Pine is usaully found where it gets cold and wet. Blasa is dry and hot. Which one make the faster bp? Balsa. I don't know anything else that is really slow so that is the best I can come up with. But if anyone wants to disagree or agree be my guest. Don't flame it it was just a guess, remember. BTW, good question.
asilentbob Posted January 21, 2008 Posted January 21, 2008 As I understand it density of the resulting charcoal, porosity of the resulting charcoal, and volatile content of the resulting charcoal are the major points.
moof Posted January 22, 2008 Author Posted January 22, 2008 I'm reading about something called ash content, can someone explain this to me and how it affects performance?
asilentbob Posted January 22, 2008 Posted January 22, 2008 Ash is mixed sodium and potassium carbonates mostly... It forms from incomplete combustion... Its the grey stuff thats usually on charcoal though I'm sure you know that. It forms when wood is burning with ample oxygen like in the open air. When charcoal is made via a retort method the gases produced from the wood decomposing pretty much push all oxygen out of the vicinity of the wood, so it doesn't so much burn as it does decompose. Your essentially distilling the oils and such out of the wood at a high heat that results in charcoal and a lot of oils, water, gases, etc. Ash content of charcoal is just that, how much ash it contains. When properly made the ash content should be pretty low. Using wood that has been burned with ample oxygen and scraping visible ash off isn't enough. Just because you can't see it doesn't mean it isn't there. A high ash content will result in pretty slow black powder as it throws the stociometry off and cools everything down. Carbonates decompose endothermicly with the evolution of CO2. So they suck up your heat and pump out flame smothering CO2. But really you should be able to find this out yourself. Research is your best friend. How do you think we all learn so much? Actually... Blackpowder cut with strontium carbonate is a long delay composition IIRC. If anyone has any more info on this I would love to get it.
hst45 Posted January 23, 2008 Posted January 23, 2008 In the interest of pursuing better charcoal, here are some of the variables that we encounter Wood species, ratio of heart-wood to sap-wood, amount of bark present, amount of knots present, temperature of the burn, length of burn time, oxygen infiltration into the retort (cooking vessel), etc. So as Frozentech said, for the home practitioner trial and error is the only real way to tell what works. That's what's so vexing in questions like "what charcoal is best?" In my particular case "best" varies with the purpose. I favor maple charcoal for BP rockets since, for me, it seems to be the most consistent from batch to batch. Why, I have no clue. I'm currently making my lift BP with beech and it's working as well as poplar. Newsprint seems the most inconstant for me, and again, I have no clue why as my guess was that it would be the MOST consistent since is comes from a blended source that I assumed would tend to equalize and variables. As far as your concern of ash content, I believe that the best way to minimize ash content is to minimize air infiltration into your retort. If you burn, or actually distill, wood in the presence of no oxygen you drive off the alcohols and volatile oils leaving only the carbon and trace elements. If air infiltrates the cooker the carbon will burn leaving ash.
noel Posted January 26, 2008 Posted January 26, 2008 I plan on trying my hand at making some charcoal soon. Just curious, not saying it's a worthwhilte to try it... What would hapen if you pumped in say, CO2, or argon to displace any O2 in the retort? until it starts cooking? Noel.
asilentbob Posted January 26, 2008 Posted January 26, 2008 I don't think it would have very much effect since your distilling off alcohols, oils, etc for quite a while before the wood actually starts to really carbonize as I understand it. Though it could be done. Some people go so far as to wash their charcoal. Some have gone further and even done extremely dilute nitric acid wash then neutralizing with potassium hydroxide.
Tbeck792 Posted February 5, 2008 Posted February 5, 2008 I did a test on this in a lab and found that it has to do with the amount of sap that is in the wood. Thus pine burns slower since it is highly concentrated with the sap which is not very flammable and a wood like balsa is because it thend to be a little drier.
FrankRizzo Posted February 5, 2008 Posted February 5, 2008 I'm sorry Tbeck, but that doesn't jive. If the sap/sugars content was the prime factor, activated charcoal would work much better than it does. Initial moisture content is also mostly a moot point since it's all driven off at the pyrolization temp. I'm convinced that, while volatiles content does make a difference, the more overarching factor is the brittleness of the very large polycyclic, and lignin-derived compounds once pyrolized. A brittle charcoal is more apt to grind finer and become more intimately mixed with the other BP ingredients. asilentbob is correct that the initial atmosphere inside your retort doesn't need to be anything special because volatile compounds start displacing the oxygen and maintain a postive pressure system before pyrolization temps are achieved. It's only after the gases stop being evolved but the temperature remains high that you'll need to worry about shielding the charcoal. CO2 or other inert gases like nitrogen will work well, but aren't really necessary if you can seal up the exhaust holes in your retort and get your charcoal cooled down in a decent period of time.
Tbeck792 Posted February 5, 2008 Posted February 5, 2008 All i know is that when we did the experiment we extracted alot more sap from the pine and evergreeen trees in general than we did from other woods such as balsa and a oak hybrid that my teacher had growing in the class room.(it was a enviormental science/bio class)(lots of fun)
FrankRizzo Posted February 5, 2008 Posted February 5, 2008 You're absolutely right. Pine and other evergreen species contain a *lot* of sap. You'll find that they make exceptional BP compared to things like walnut or oak though.
Tbeck792 Posted February 5, 2008 Posted February 5, 2008 True!! it must have someting to do with the acuall structure of the wood...Maybe ill do a test with a red wood since that should make some really crappy BP if this theory is righthaha
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