Tertiary Air Query

[neiln]

On 27/11/2020 at 23:47, Ratman said:

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.

 

Same Stockton 5 here and same burn. I agree it feels like it could shut a good bit more and still be clean.

[Mik the Miller]

12 hours ago, openspaceman said:

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.

 

Well that clears that up then 

 

[openspaceman]

2 hours ago, neiln said:

Same Stockton 5 here and same burn. I agree it feels like it could shut a good bit more and still be clean.

IMO if you don't shut down until only char is left it would be clean and only send CO up the chimney till the fire goes  out from air starvation. The thing is people would stoke it up with fresh wood and then shut it down, b to keep it in all night, the wood would then smoulder on emitting PICs by having a fixed minimum air supply the idea was that there would always be enough air to keep a flame.

 

On mine I had the impression this fixed miniumu air came in the small jets at the back but studying it now I'm unsure.

 

It's a Morso 11 and the air leaver has a central position  for minimum, pushed to the left is for air under but I never use that and suspect the pssage has blocked with ash, to the right controls the over air for wood burning, I assumed this only controlled the air wash, the inlet for which is many many times the area of  the small air jets at the back. It is the same size and shape as the flue opening and air is heated by the flue as the two streams are only separated by a 3mm steel plate.

 

This is why I think it i important to get the stove up to operating temperature quickly and keep it there so the air wash is  mixing hot air into the flaming region and not quenching the flame.

[openspaceman]

3 minutes ago, Mik the Miller said:

 

Well that clears that up then 

 

Sorry not meaning to be authoritarian on this, we're all learning

[Mik the Miller]

35 minutes ago, openspaceman said:

Sorry not meaning to be authoritarian on this, we're all learning

 

No need to apologise, we are learning ...

 

 

I was trying to simplify ... there are 3 ways the air gets into a wood stove (not counting opening the door).

 

Pa - Primary Air from the bottom of the stove in the case of a multifuel, under the grate.

Aa - Airwash, often directly above the top of the door/glass

Sa -  Secondary or Tertiary or Cleanburn air which arrives preheated, through small hoiles in the back of the stove 1/2 way up the firebox.

 

Typically you have active control over the Pa and Aa whilst the Sa is pre-set (although it can be varied when the stove is cold).

 

@Jimmy101 it looks like your Sa isn't letting any air in at all. You do need some and then you can close the Pa and Aa down fully. In that state you will see the air 'burning' above the logs, If the stove isn't hot enough (it is in your vids) you would see black fingers in the flames above the logs as the cold air punches through the flames.

 

You are very close.

Crack the Sa open a little (25%) and then you can control the fire (once its going up to temp and the Pa shut) with the Aa open 5 to 10%

If the flames are raging above the logs then shut the Sa to 10%

If the fire dies off to nothing (with Pa and Aa shut) then open Sa to 50%

 

It's a balancing act - you're close 

 

Edited November 29, 2020 by Mik the Miller

[Stubby]

On my Burley there is only 1 air control ( well 2 if you count the door )  It is a slide that goes from left to right ( L being closed R being fully open ) . There are rows of small air holes down the 4 corners of the fire box ( all chasing each other in direction of the jets ) and a row of glass wash holes across the top just above the door .  It is as simple as a simple thing and works perfectly . Light fire . Have the door open a crack and air slide fully open . This heats the flue . Close the door fully , air slide still fully open . When stove body is up to temp you want close air slide almost completely . Never fails .

[pancakedan]

I like to run my stoves hot and fast and control the heat by the amount of wood being burned. Once up to temp, I close down the primary air and rarely close the secondary/airwash.

[neiln]

6 hours ago, openspaceman said:

IMO if you don't shut down until only char is left it would be clean and only send CO up the chimney till the fire goes  out from air starvation. The thing is people would stoke it up with fresh wood and then shut it down, b to keep it in all night, the wood would then smoulder on emitting PICs by having a fixed minimum air supply the idea was that there would always be enough air to keep a flame.

 

On mine I had the impression this fixed miniumu air came in the small jets at the back but studying it now I'm unsure.

 

It's a Morso 11 and the air leaver has a central position  for minimum, pushed to the left is for air under but I never use that and suspect the pssage has blocked with ash, to the right controls the over air for wood burning, I assumed this only controlled the air wash, the inlet for which is many many times the area of  the small air jets at the back. It is the same size and shape as the flue opening and air is heated by the flue as the two streams are only separated by a 3mm steel plate.

 

This is why I think it i important to get the stove up to operating temperature quickly and keep it there so the air wash is  mixing hot air into the flaming region and not quenching the flame.

Yes I think that's the aim of the smoke control kit, and I agree with the aim.  I just think it seems like it could close down more then it does on the Stockton.  It's hard to have any real control once the stove has been going a few hours and the flue is really warm and the draw it's very strong.  If I put two dry logs then I'll get a flue temp of 280+C, if the wood is Holly or yew I dare not put two logs on. Although one log gets lonely and sulks so I need to mix Holly and yew with something like Oak.

 

It's not a bad stove for the money, but next time I buy a stove I reckon I'd spend more.  A Burley maybe.  From stuff I've read there are a few stoves with more control then the Stockton.

Edited November 29, 2020 by neiln

[Jimmy101]

6 hours ago, Mik the Miller said:

 

 

@Jimmy101 it looks like your Sa isn't letting any air in at all. You do need some and then you can close the Pa and Aa down fully. In that state you will see the air 'burning' above the logs, If the stove isn't hot enough (it is in your vids) you would see black fingers in the flames above the logs as the cold air punches through the flames.

 

You are very close.

Crack the Sa open a little (25%) and then you can control the fire (once its going up to temp and the Pa shut) with the Aa open 5 to 10%

If the flames are raging above the logs then shut the Sa to 10%

If the fire dies off to nothing (with Pa and Aa shut) then open Sa to 50%

 

It's a balancing act - you're close 

 

The issue i am having is as soon as i open the tertiary (Sa) plate on the back regardless of where its set doesn't seem to provide the effect i am after, if anything it decreases the performance of my fire. This is why i ended up shutting it becuase the fire was performing better without. 

 

My main issue with the Sa open any amount is that the kindling burns so rapidly that its basically gone by the time my smaller logs on the top have even had chance to ignite. If i reduce the Aa to combat this for a steadier burn then this starves the fire of the oxygen it needs at this stage. 

 

It really looks to me as though the air is getting in but is just getting sucked up the flue instead of circulating the firebox.  Would a flue damper perhaps help the firebox retain some heat and help the air get to where it needs to? Or does this then prevent as much air getting in as well? 

 

At the end of the day the fires im getting arent horrendous. I can get it running at a good temperature .but im just not getting the burn characteristics i would expect and dont feel like i have any control over the burn rate with the air controls. Over the course of the night the fire dies because the logs arent burning down to a decent set of embers for the next logs to be added and they dont burn evenly at all. 

 

Overall i appreciate its a balancing act but it seems to be too much faffing about at the minute and i just cant put my finger on it.

[Stubby]

13 minutes ago, Jimmy101 said:

The issue i am having is as soon as i open the tertiary (Sa) plate on the back regardless of where its set doesn't seem to provide the effect i am after, if anything it decreases the performance of my fire. This is why i ended up shutting it becuase the fire was performing better without. 

 

My main issue with the Sa open any amount is that the kindling burns so rapidly that its basically gone by the time my smaller logs on the top have even had chance to ignite. If i reduce the Aa to combat this for a steadier burn then this starves the fire of the oxygen it needs at this stage. 

 

It really looks to me as though the air is getting in but is just getting sucked up the flue instead of circulating the firebox.  Would a flue damper perhaps help the firebox retain some heat and help the air get to where it needs to? Or does this then prevent as much air getting in as well? 

 

At the end of the day the fires im getting arent horrendous. I can get it running at a good temperature .but im just not getting the burn characteristics i would expect and dont feel like i have any control over the burn rate with the air controls. Over the course of the night the fire dies because the logs arent burning down to a decent set of embers for the next logs to be added and they dont burn evenly at all. 

 

Overall i appreciate its a balancing act but it seems to be too much faffing about at the minute and i just cant put my finger on it.

Get a Burly . ☺️