Tertiary Air Query

[Mik the Miller]

Here's my new fire going strong, not flat out but burning well. You can see the logs and the yellow flames and then above the tertiary air burning the gasses.

Initially I had the secondary/tertiary air vent fully open but hacve found that with it closed down to about 1/2 and with a little primary/airwash I can find it's efficent/happy spot. I am still learning and may close the tertiary air down a little more to get a more 'lazy' effect.

[Jimmy101]

3 hours ago, Mik the Miller said:

Here's my new fire going strong, not flat out but burning well. You can see the logs and the yellow flames and then above the tertiary air burning the gasses.

Initially I had the secondary/tertiary air vent fully open but hacve found that with it closed down to about 1/2 and with a little primary/airwash I can find it's efficent/happy spot. I am still learning and may close the tertiary air down a little more to get a more 'lazy' effect.

The flames on yours look so much slower and darker orange than mine. My flames tend to be quite yellow but really turbulent almost as if the air Is blowing them about. Im starting to wonder if my firebed is too narrow for some of the logs im putting on. The logs only tend to ignite underneath and at the back. 

 

Because its a slimline stove and has a multifuel grate it doesn't actually leave a massive asive amount of room. If you get the wood only version of this stove you can get a miltifuel conversion kit. Im wondering if i can convert this one to wood only which would give me a bigger area. 

 

Ive toyed around with the tertiary and the more i open it the worse the fire gets. The kindling burns like mad but then it burns that fast the logs haven't ignited before the bed of embers is virtually gone.  Ive shut it again now but im still convinced something isnt right. Having said that on some occasions i have a brilliant fire and cant put my finger on what i did differently. 

[Ratman]

The flames on yours look so much slower and darker orange than mine. My flames tend to be quite yellow but really turbulent almost as if the air Is blowing them about. Im starting to wonder if my firebed is too narrow for some of the logs im putting on. The logs only tend to ignite underneath and at the back. 
 
Because its a slimline stove and has a multifuel grate it doesn't actually leave a massive asive amount of room. If you get the wood only version of this stove you can get a miltifuel conversion kit. Im wondering if i can convert this one to wood only which would give me a bigger area. 
 
Ive toyed around with the tertiary and the more i open it the worse the fire gets. The kindling burns like mad but then it burns that fast the logs haven't ignited before the bed of embers is virtually gone.  Ive shut it again now but im still convinced something isnt right. Having said that on some occasions i have a brilliant fire and cant put my finger on what i did differently. 

Are you running a DEFRA smoke control kit? If so then they dont allow you to shut the fire down fully, they allow a certain amount of air in at all times to give the cleanest burn. I have one fitted cos i’m in a smokeless zone. Giving tertiary air only increases its ferocity, wish i could shut mine down just that little bit more but it is what it is unfortunately for me. (Unless i put the original adjusting bar back in the front [emoji6][emoji16] but i just go with it)

[Jimmy101]

5 minutes ago, Ratman said:

Are you running a DEFRA smoke control kit? If so then they dont allow you to shut the fire down fully, they allow a certain amount of air in at all times to give the cleanest burn. I have one fitted cos i’m in a smokeless zone. Giving tertiary air only increases its ferocity, wish i could shut mine down just that little bit more but it is what it is unfortunately for me. (Unless i put the original adjusting bar back in the front but i just go with it)

Not that im aware of if i shut all my vents it definitely kills the fire. This is why im confused as i would expect to open the tertiary and it increase the burn rate but it does the opposite really. 

[Ratman]

Not that im aware of if i shut all my vents it definitely kills the fire. This is why im confused as i would expect to open the tertiary and it increase the burn rate but it does the opposite really. 

Hhmmmmm [emoji848][emoji848]

[openspaceman]

How long has it been burning and since the last log went on?

 

Somehow there isn't enough air  getting to the offgas as a very fuel rich flame is going up the flue.

 

The air holes at the back are having to provide too much of the air to counter this, the result is you have the flames still burning (and being quenched) into the flue. if you could see outside I think it would be brown smoke.Try to decrease the air wash and cut out primary air so the fire just dances over the logs.

 

Is the door sealing shut? With my Morso sometime the ash tray sticks out a bit proud  because I haven't clean the ash spilled at the back and this stops the bopttom rope sealing.

[Mik the Miller]

I think we need to get some of the terms agreed here.

 

The Primary air (Pa) comes in underneath the grate (on a multifuel).

The Airwash (Aa) comes from the top (often through the door frame) and washes down the glass.

The Secondary (or Tertiary or Cleanburn) air (Sa) comes in behind the back air brick and enters though some holes which are around 2/3rds of the way up the back brick. This air enters via a closed section that often runs down the outside back of the stove and is therefore heated prior to entering the firebox.

 

The Cleanburn/Tertiary/Secondary (Sa) air is not often controllable when the fire is burning. Its via a fixed aperture that can be varied by a flap that is bolted in position.

Some stoves have separate Pa and Aa controlls, mine has a single 'lever' that when fully open allows air in via the Pa and Aa vents. Pull it to the next notch and it shuts the Pa fully, Aa is fully open, pull it again and it closed the Aa and the Pa. The Sa is always letting in air.

 

My Sa is possibly a bit wide as the gasses are quite turbulent.

To get the fire to burn as per the video, I almost close the Aa (leave the Aa slightly open and have the Pa shut). The fire has been on for a while (20 mins ish) to get to this happy state with the Pa shut and the Aa open, then I start to nudge the Aa shut and watch the gasses ignite and the logs go from yellow flames to a red glow.

 

It happens slowly though. Like a turning a big boat. Once its in the right position it stays like that for a while. Dry Oak or Beech last longer than S Birch or Chestnut and longer than Pine or Larch. When I add more wood I need to open up the Aa (as the freshly introduced wood cools the internals of the stove) and after a few minutes nudge it closed so that the Sa takes over (becoming the dominant).

Wet wood kills it and it takes longer to get to the happy state.

Oak takes longer than Pine.

The stove has to be hot for it all to work. Mine is a nominal 7.5KW and to get up to this output takes around 20 mins of intense burning with the Aa fully open.

 

@Ratmanhas mentioned the DEFRA smoke control kit. This 'setting' always lets Pa in, it won't let you shut it down, however, this kit is normally a plate that can be removed. My stove (as an example) came with this plate (called the 'Smoke Control Facility') in a bag with instruction that it "must be fitted to meet the requirements of a smoke control area". If the 'kit' was fitted I wouldn't be able to get the stove to burn as in the video, the Pa and Aa would overide the Sa.

 

Hope that makes sense ?

 

 

 

[Ratman]

My smokeless control kit consisted of a replacement bar which swaps out with the original situated in the stove body above the door which you label as Aa, it has a different assortment of metal cut outs along its length compared to the original and the control lever fits through a different aperture in the stoves casting above where the original bar would fit. To fit it you have to drop the box from within the top of the stove (Stockton 5 midline) there is less adjustment with the defra bar once fitted compared to the original (left for more air, right for less air) and i personally feel it is SHAT and a bad design which allows too much air in still when in its most shut down state. My tertiary air is a simple sliding plate at the bottom underside of my stove towards the rear, and my primary air is at the bottom of my door (again simple left for more air, right for less air) When the fire is fully up to temp and in its fully shut down state my flames are not naturally slow rolling flames they are slightly fierce and fast dancing, more so than in your short vid, hence my thoughts on it being a bad afterthought/get around scenario regards the smoke control kit, i think it could stand to be shut down a little more and still be “clean burning” regards defra regs. I must say though that the draw on my chimney/flue (have a liner installed, not open chimney) is extremely good so this will also exaggerate the situation i feel.

 

[Jimmy101]

Couple of videos of mine going this eve.  Tertiary air plate on the rear is shut in both videos. Primary vent also shut in both. I tried with tertiary cracked but it seems to have the opposite effect of what you would expect. 

 

First video is with air wash fully open

 

 

Second video is with airwash set about 25% open. It only needs to be nudged a tiny bit more closed and no air gets in and it dies off.

[openspaceman]

22 hours ago, Mik the Miller said:

think we need to get some of the terms agreed here.

 

The Primary air (Pa) comes in underneath the grate (on a multifuel).

The Airwash (Aa) comes from the top (often through the door frame) and washes down the glass.

The Secondary (or Tertiary or Cleanburn) air (Sa) comes in behind the back air brick and enters though some holes which are around 2/3rds of the way up the back brick. This air enters via a closed section that often runs down the outside back of the stove and is therefore heated prior to entering the firebox.

Okay but you cannot then dictate what the terms mean when the science has previously agreed something different and why introduce abbreviations, or am I the only one with a supershort short term memory who has to go back and read a glossary before giving up?

 

The air wash is just that, it washes down the glass. Most of the time it is supplying secondary air but the nature of burning wood, where 70% of the heat comes from volatiles, (gases and vapour), which burn with a flame is that you must supply excess air for a clean burn in order to guarantee a fuel molecule meets an oxygen molecule. With wood this excess air means supplying 150-200% of the stoichiometric air. A petrol engine is supplied with damn on 100%  stoichiometric air, a diesel ~120% and a gas boiler around 110% ( because gas is premixed in front of the burner and a simple compound to burn).

 

Coal fires need primary air to gasify the carbon to CO2 and CO  which then burns in the secondary flame, wood  burns cooler, and if it were heated to a typical firebox temperature of ~800C  in the absence of air only 15% of the dry weight would be solid carbon, this small amount doesn't have to be gasified as it will simply sit happily at the bottom of the fire glowing red and mostly producing CO2 with a small amount turning to CO and burning in the secondary flame.

 

It takes time for the firebricks to heat up and the flue to start drawing well, before everything gets hot enough the flames will be yellow because the carbon particles exist in the flame longer. As the fire heats up the residence time shortens and the carbon particles get burned out quicker.

 

I think the preheated air from the  holes at the back can be secondary and excess air, they are there to maintain a flame because smouldering is sending Products of Incomplete Combustion up the flue.

 

Typically PICs will be particulates and they will show as a blue wisp out of the chimney, they mostly come from the secondary flame that has not had time to burn out through being quenched, either by a cold surface or a low firebox temperature ( from wet logs) or from too much excess air.

 

I have been unable to download @Jimmy101's videos yet but his flue temperature looks to be in the right range for a good hot burn.

 

I would note were this a commercial boiler this would be an uneconomic range to exhaust the boiler and you would typically aim for 110C, the 100C difference would represent a 10% loss.