Burn Pattern

Canugghead

After a 12h 250F smoke, controlled by FB500, I noticed a large crater near the front intake vent. The dip was big enough to swallow the DFMT with room to spare. I don’t recall seeing such a distinct ‘hole’ with my old Stoker, is the significant difference due to variable speed vs constant speed fan? Also wondering if burn would be more even when a KAB is used with FB? Or, if the firebox vent is turned 90 or 180 degrees away from the bottom vent?I know I’m overthunking this 

Edit: just remembered it was windy the first few hours and the temp rose almost 10F over set temp.

Langner91

I think it is more a situation where your small pieces of lump (relatively speaking) were too densely packed.  That caused your fire to "follow the oxygen" and burn out in front of your vent.

If you had more big pieces in the back, it wouldn't do that.  

I would also make sure your firebox holes aren't plugged in the back.

At least it didn't go out!

fishlessman

i think its more random, have had center burn a few times over 20 or so years and i dont use a fan. only way to make sure it doesnt effect the cook is to use a poker and or a wiggle stick. but it doesnt happen often enough to concern me. you can usually catch it when you see the temps drop. its only happened to me maybe twice, but is a reason to dump the lump in and give it a stir  so the lump is touching more pieces uniformly

Canugghead

Langner91 said:

I think it is more a situation where your small pieces of lump (relatively speaking) were too densely packed.  That caused your fire to "follow the oxygen" and burn out in front of your vent.

If you had more big pieces in the back, it wouldn't do that.  

I would also make sure your firebox holes aren't plugged in the back.

At least it didn't go out!

I filled mostly with medium sized lumps, then topped with smaller pieces to fill the spaces, you're right about packing too tight. All holes were clear to start but could have been obstructed by the smaller pieces. FB did a good job of holding temp after the initial spike caused by high wind, I think. Thanks for chiming in.

Canugghead

fishlessman said:

i think its more random, have had center burn a few times over 20 or so years and i dont use a fan. only way to make sure it doesnt effect the cook is to use a poker and or a wiggle stick. but it doesnt happen often enough to concern me. you can usually catch it when you see the temps drop. its only happened to me maybe twice, but is a reason to dump the lump in and give it a stir  so the lump is touching more pieces uniformly

Come to think of it, I probably experienced it many times over the years sans fan controller...typically temp would drop about halfway through the cook and I'd poke the bottom and from above through the platesetter gaps. Since I did that without removing anything I would have missed the visual evidence of the problem. May be it's the way I load the firebox. Thanks for your input.

Mark_B_Good

Me thinks that ash and small pieces (bug dust) blocked the airflow in the back of the unit.

Canugghead

Mark_B_Good said:

Me thinks that ash and small pieces (bug dust) blocked the airflow in the back of the unit.

Small pieces at top centre only. Zero ash since I cleaned out the egg before reloading with big pieces at bottom,  followed by medium, than small.

Mark_B_Good

Canugghead said:

Mark_B_Good said:

Me thinks that ash and small pieces (bug dust) blocked the airflow in the back of the unit.

Small pieces at top centre only. Zero ash since I cleaned out the egg before reloading with big pieces at bottom,  followed by medium, than small.

Interesting ... was the blower angled funny at all?  

Canugghead

Mark_B_Good said:

Canugghead said:

Mark_B_Good said:

Me thinks that ash and small pieces (bug dust) blocked the airflow in the back of the unit.

Small pieces at top centre only. Zero ash since I cleaned out the egg before reloading with big pieces at bottom,  followed by medium, than small.

Interesting ... was the blower angled funny at all?  

Blower tilts up slightly, has to follow the tapered contour of egg bottom.

Mark_B_Good

OK, I can see how that could lead to an odder burn path ... but did you say you've used this exact blower before ... same setup, and this is the first time you've seen this burn path? Or is this the first time trying this setup?

Canugghead

Mark_B_Good said:

OK, I can see how that could lead to an odder burn path ... but did you say you've used this exact blower before ... same setup, and this is the first time you've seen this burn path? Or is this the first time trying this setup?

First time using FB with Large, used Stoker before.

Botch

This has happened to me, once, on an overnight cook sans any blower.  My lo-temp alarm went off at OMG:30 am, and I pulled the brisket/platesetter and the lump had burned straight down, in about an 8" circle (I light with a single square in the center), and the surrounding lump was untouched.  I could've dropped a coffee can down the hole.  A quick stir and it burned fine the rest of the night.  
Has never happened since; I think it's just a really odd coincidence, like when a whole California neighborhood burns during a wildfire, except for that one house.  

stlcharcoal

I had one in the XL where it burned on side and then underneath the other side.......so much that there was a shelf of lump with a cavern underneath you could have fit a softball into.  I have a pic, but it doesn't do it justice.

I really don't think there's a pattern on low and slow.....hot and fast yes, but it just meanders around on a low and slow following whatever fire bridge it can find. 

Canugghead

@stlcharcoal Thanks, I think you nailed it. I’ve seen so called cavern occasionally including this cook, with or without controller. Also agree with pic not doing justice, in this case I had to drop the DFMT in it to illustrate.

stlcharcoal

I've done plenty of low and slows where I had wood chips in it that were still brown after a 16 hr cook.  They are darker than when they started because of the smoke and heat, but they never burned or even carbonized because the fire never got anywhere near them.....and it only takes a kindling temp 375-400F to ignite wood. 

Gotta throw out all the internet lore and "best practices" of smoking when it comes to kamados.  They use so little O2 because such a tiny little ball is burning at any given time.  They are a totally different animal.