burning clarification

[NYBurner]

OK - hoping to get some clarification here regarding burn and optimization.

If I have a big FAT dark orange flame which we commonly refer to as a 'dirty' burn, is this a result of too much oxygen or deprived oxygen?

I ask this because the stove firebox is run in vacuum....if I open the door I get the 'dirty burn' (like a common fireplace).

Im asking this because of discussion I see regarding OAKS and altering trims in various threads......and I think understanding this would help a lot of people.

 

[johneh]

Remember a pellet stove flame is force feed air . Air is sucked through the burn pot
The 3 basic flames are
1 orange with black tips a lazy , fire place type of flame
2 bright flame blue white with a little orange very lively .
3 Blow torch like the cutting tip of an oxy acetylene torch
Number 2 is what you want hot and clean burning
Adjust the air going to the burn pot by what ever means
the adjustment is made by your stove
Here's a video

 

[heat seeker]

Probably not so directly about oxygen, but about the rate of airflow, which does affect the oxygen supply. More air movement means more oxygen. A lazy flame, while it can access O2 directly from the air, is caused by a lack of airflow. The black tips are unburned fuel, again a lack of O2.

 

[NYBurner]

Ok - to my point then, this is a burn box not a motor pumping under compression. So in reality running it as lean as possible would be ideal, correct?

 

[heat seeker]

The burn air is being drawn through the burn area, so it is under a very slight vacuum. Running too lean would imply a large airflow, which would cause excessive heat loss through the exhaust. There is a balance to be maintained between enough airflow, and too much.

Very old pellet stoves pushed the air through the burn area, so were under very slight pressure. This design, AFAIK, has been totally discontinued.

 

[Deezl Smoke]

Ok - to my point then, this is a burn box not a motor pumping under compression. So in reality running it as lean as possible would be ideal, correct?

No. The same basic principles pertain. A "proper" fuel to air ratio needs to be found. Too much fuel, soot and creosote build up and very inefficient use of fuel. Too much air, heat is forced past the exchanger means too fast and a lot of heat ends up outside to no benefit to you. It also usually blows pellets out of the burn pot before they are completely burned, which also reduces the amount of heat transferred to the exchanger where you can get it into the house.

On some stoves like the Castle Serenity that I use, there is a combustion air inlet gate adjustment and a combustion fan speed adjustment. They complement each other to compensate for OAK installation designs and exhaust chimney designs.

A long crooked chimney may need a lot of fan, but a short straight OAK or no OAK may not need much fan. So to compensate, you would run more fan for the chimney, but close down the inlet air gate to keep the pellets in the pot. Remember, you are adding fuel to the air so there will be more exiting the exhaust than coming into the combustion from the OAK.

 

[NYBurner]

heat seeker - Yes that is the design in M55...so basically, it is a pocket of atmospheric air enveloped in a vacuum correct?

how would it cause excessive heat

No. The same basic principles pertain. A "proper" fuel to air ratio needs to be found. Too much fuel, soot and creosote build up and very inefficient use of fuel. Too much air, heat is forced past the exchanger means too fast and a lot of heat ends up outside to no benefit to you. It also usually blows pellets out of the burn pot before they are completely burned, which also reduces the amount of heat transferred to the exchanger where you can get it into the house.

On some stoves like the Castle Serenity that I use, there is a combustion air inlet gate adjustment and a combustion fan speed adjustment. They complement each other to compensate for OAK installation designs and exhaust chimney designs.

A long crooked chimney may need a lot of fan, but a short straight OAK or no OAK may not need much fan. So to compensate, you would run more fan for the chimney, but close down the inlet air gate to keep the pellets in the pot. Remember, you are adding fuel to the air so there will be more exiting the exhaust than coming into the combustion from the OAK.

I have an enviro M55...there is no inlet adjustment or fan. There is only an exhaust damper and exhaust fan to play with in regards to airflow. I can/have alter pellet feed rate as well.

a proper ratio but it also needs to account for the chamber volume and mass then as well. I am kind of thinking that the M55 just requires to be run a bit 'harder' to be happy than smaller stoves?

 

[heat seeker]

I'm not sure what you're asking. The entire burn chamber is typically under a slight vacuum, with a good airflow to support the fire. You could only get too much heat by providing too much fuel for the heat exchanger to remove, as far as I know. I think that the only purpose for the vacuum is to provide airflow and to prevent smoke from escaping into the room.

 

[NYBurner]

I'm not sure what you're asking. The entire burn chamber is typically under a slight vacuum, with a good airflow to support the fire. You could only get too much heat by providing too much fuel for the heat exchanger to remove, as far as I know. I think that the only purpose for the vacuum is to provide airflow and to prevent smoke from escaping into the room.

ok...if I have a 'sealed' chamber in vacuum with a flame, fuel and a fresh air feed....then essentially there is a region of oxygen (the burn/flame area) surrounded by oxygen depleted air (the rest of the chamber area) that is perpetually in vacuum correct?

 

[johneh]

Vacuum is being used incorrectly . Inside the stove is an area of low pressure
as compared to atmospheric pressure. Fire as we know it does not or can not
exist in a vacuum

 

[Deezl Smoke]

ok...if I have a 'sealed' chamber in vacuum with a flame, fuel and a fresh air feed....then essentially there is a region of oxygen (the burn/flame area) surrounded by oxygen depleted air (the rest of the chamber area) that is perpetually in vacuum correct?

The exhaust fan and damper are also your inlet fan and damper. The exhaust fan is in the hot air side of the burn chamber. It "pulls" air into the burn pot where fuel is added. As long as the exhaust fan is running and the damper is open some, there will be new air coming into the fire at all times. The fire and fuel do burn and deplete the oxygen above the fire, but new oxygen is coming in at the bottom at all times that the fan is running.

So the exhaust fan runs double duty. It "pulls" air into the fire, and "pushes" depleted air our out the chimney. The inlet side of the fan pulls, and the oulet side pushes.

The only way for no fresh air to come into the fire is either the fan has stopped or an obstruction is in the combustion inlet pipe.