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Airflow & Smoke
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Thomas P.
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Joined: 27 Jul 2005
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Location: Texas

PostPosted: Tue Feb 07 06 2:07 am    Post subject: Airflow & Smoke Reply with quote

I'm trying to explain to some folks the different effects of airflow on smoke, and wanted to check with the Peanut Gallery first to make sure I had my facts correct. I'd sure appreciate the help.

Proper air intake and Proper exhaust = sweet, blue smoke

excess intake = fire too hot, no smoke

deficient intake = fire too cool, lots of heavy white smoke

deficient exhaust = fire gets congested and smoke gets stale, but what "color" of smoke would you have?

Thanks again fellas!
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Alien BBQ
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PostPosted: Tue Feb 07 06 3:16 am    Post subject: Reply with quote

Yellow with cyanide gas.

Here's the difference, right smoker =good, left smoker =bad.


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Thomas P.
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PostPosted: Tue Feb 07 06 3:34 am    Post subject: Reply with quote

Okay, and you get creosote from wet wood, correct?
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Alien BBQ
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PostPosted: Tue Feb 07 06 3:37 am    Post subject: Reply with quote

You get creosote from all wood; it is just a matter of degree. The higher (noticeable) levels come from green wood and large amounts of wet wood.
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MacMitch
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Joined: 22 Dec 2005
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Location: Alpharetta, Georgia

PostPosted: Thu Feb 09 06 7:14 am    Post subject: Reply with quote

I have been studying up on this smoke thing & plan to make a separate post regarding what I found. My reason to post here is I believe we often leave out a major factory in our discussion of making that blue smoke. Yes the air is important but it will not burn on its own, the wood has to be heated to form a vapor. The factor that we forget is the surface area of the wood we are burning. Wood has to burn from the outside in, thus a fire with more wood surface area will burn hotter, faster, more efficiently and produce that blue smoke.

That is if you take a large log & toss it in a fire a very limited part of the wood is exposed to the heat & burns, its pretty easy to see this burning larger wood in a fire. Take that same piece of wood & split it into smaller pieces & arrange it in the fire box so that the maximum amount of its exterior is exposed and you get an exponential increase in its ability to convert to a gas unite with the air & combust cleanly. That exponent is in fact quite large and just as or even more important than the amount of air reaching it.
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Alien BBQ
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PostPosted: Thu Feb 09 06 8:24 am    Post subject: Reply with quote

You are really close, increasing the surface area does increase the amount of fuel available but it also changes the air fuel ratio. You can have no fire in a fuel rich environment. Another factor that changes when you add more wood is the combustion temperature of the fire. Because fire is actually a chemical reaction, when you reduce the optimum temperature for combustion you create gaseous by-products and a cascade effects happens until the fire reaches homeostasis and the increase of fuel starts to increase the temperature of the fire proportionately in small steps in relation to the amount of air and temperature. When we look at a fire, the wood is not actually burning, through a process called pyrolysis the wood decomposes at a rate that releases combustible gasses, and they are what actually burn. The drier the wood, the faster this process happens at the correct temperature. Wet wood releases these same gasses but the temperature prevents any sustainable combustion. The best way to increase a fire’s burning potential is to add small amounts of fuel in incremental steps. This will prevent the temperature drop and will eliminate the possibility of by-product production.
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BBQMAN
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Joined: 13 Jun 2005
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PostPosted: Thu Feb 09 06 8:51 pm    Post subject: Reply with quote

Nice description there Michael! Very Happy

That would (wood!) explain why I have no trouble getting good burn with whole DRY logs. My smoker might of course be the exception here, as it does take a good sized fire to maintain proper heat. Smaller splits are just not practical, and my logs probably equate to throwing wood chunks into the "average" sized smoker. Very Happy

I did find that a smaller charcoal fire with some smaller wood pieces did work well with my old New Braunfels. As most of us know, temp. control is a major issue with that design. I finally went with a gas log lighter, and smaller splits to achieve good results. The NB only need a small fire to maintain correct temp. A fire large enough to support a log fire was just too hot! Shocked

The size of your equipment, weather conditions, fuel used etc. is all a factor for fire management and a good clean burn!
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Thomas P.
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PostPosted: Thu Feb 09 06 9:37 pm    Post subject: Reply with quote

I start out with 5 or 6 briquettes in the bottom of a chimney filled with a mix of lump and pieces of dried oak...







...then I use quarter splits of 16" hickory logs for smoke...



...and I usually never have a problem summoning the Blue Smoke Fairy!


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BBQMAN
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PostPosted: Thu Feb 09 06 9:45 pm    Post subject: Reply with quote

Looks good! What temp. does your smoker run with that sized fire?

HMMMMMMMMM, the "blue smoke fairy" sounds like the sequel to Broke Back Mountain! Shocked Laughing
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MacMitch
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PostPosted: Thu Feb 09 06 10:20 pm    Post subject: Reply with quote

Nice fire there ThomasP!

Hmm, I am not sure I follow everything you are saying there Alien.

My understanding is that the wood has to turn to a vapor to combine with oxygen & burn. For the wood to turn to a vapor its surface has to reach 212-214 degrees. The surface of the wood basically has to dry out enough to burn which happens when its surface reaches that temperature range.

When you start talking about all the expanding gases the subject increases very quickly in complexity. The gases are expanding & contracting with temperature changes everywhere they are created & move. As I understand it its impossible to measure or even calculate the vapors within a smoker or recovery boiler, which is why what is in the "air" inside such devices & the "air" escaping is measured by weight instead of volume.

My point goes back to the simple basic fact of the importance of exposed wood surface area per weight of wood. Actual combustion can only occur after the wood surface area is heated to 212-214, dries enough to make vapor & combine with oxygen.

As I understand it, a discussion of the vapors created by the chemical reaction that is the fire is pretty pointless even for experts as you would have to include an exact location at any given exact point in time in an infinite number of locations & points in time.
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Last edited by MacMitch on Fri Feb 10 06 8:59 am; edited 1 time in total
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BBQMAN
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PostPosted: Thu Feb 09 06 10:29 pm    Post subject: Reply with quote

Shocked

And your point is.............................?
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Thomas P.
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PostPosted: Thu Feb 09 06 11:11 pm    Post subject: Reply with quote

BBQMAN wrote:
Looks good! What temp. does your smoker run with that sized fire?


I get it up to about 300 to 325 before I put the meat on. Of course, that cools the whole rig back down. Then I use the intake to control the heat at about 225 to 250.

As soon as I put on the meat, I start my first reload chimney. One thing I've noticed about some folks, they start a chimney and then dump it in as soon as the chimney is ready, regardless of what the pit needs at that time.

I just keep the chimney going until I need it. As it cooks down, I just keep adding wood/charcoal to the top to keep it full. Yes, I do go through a lot of fuel that way, but it's worth it!


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MacMitch
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PostPosted: Fri Feb 10 06 3:47 am    Post subject: Reply with quote

My point is:

1) we can adjust our fires to create that blue smoke with the size, shape & organization of the wood we place in it.

2) the gases & vapors inside our smokers are changing so much & so fast that adjusting them does not lend itself to any sort of constant rules that we can count on.

Or as one point: adjusting air flow in a smoker is in no way a constant, it has to be adjusted for every fire as it burns whereas the size & shape of our wood & how we feed it into the fire is a constant that we can plan for and control any fire with.
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edskull69
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PostPosted: Sat Feb 11 06 11:32 pm    Post subject: Wow !! Reply with quote

Who would have ever thought there was this much science in cooking meat !!! LOL When I got my smoker I never dreamed it would be as hard as it is to smoke ribs and maintain a temp in that thing! I am a boiler operator. There is something called the combustion triangle. Air, fuel, temp. I never thought it would be so hard to get the right formula to maintain the temp in my smoker. I respect everybody who can do it. Smoking is truly an ART ! The finished product is pureheaven. I salute all of you guys that can get it right.
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Jeff T
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PostPosted: Sun Feb 12 06 12:12 am    Post subject: Reply with quote

Science, Art ? Or just plain fun....
I`m just having fun trying to figure it all out and the best part is family and friends think i`m some kind of BBQ Guru. Laughing
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MacMitch
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PostPosted: Sun Feb 12 06 4:18 am    Post subject: Reply with quote

Hi edskull69, who do you operate a boiler for? GP maybe thats where my buddy use to work.
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edskull69
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PostPosted: Mon Feb 13 06 2:36 am    Post subject: Reply with quote

I work for a refinery in south jersey at tha power house
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edskull69
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PostPosted: Mon Feb 13 06 2:36 am    Post subject: Reply with quote

the Embarassed
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edskull69
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PostPosted: Mon Feb 13 06 2:36 am    Post subject: Reply with quote

the Embarassed
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edskull69
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PostPosted: Mon Feb 13 06 2:37 am    Post subject: Reply with quote

the Embarassed
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