Post by rakettimuurari on Nov 24, 2017 13:34:21 GMT -8
Just finished 160mm BR which is working and heating nicely.
Only one oddity/ problem remains: The system requires much more combustion air (ca. 35% of CSA) than estimated 25% of CSA/ about 40+10cm2
For background: donkey32.proboards.com/thread/2308/brick-sidewinder-riser-baking-oven
SKP: design
First the channels in cast iron door were enlarged to be bit larger than the desired air intake size, about 53cm2. This was not enough to let the fire burn briskly and the rocket sound to get started. However everything was fine if door remained bit open. Bit later when the chimney damper was installed, it was found that actually the chimney stack is about 8% narrower near the ceiling compared to its 160x160mm diameter elsewhere, Which I let to dictate my system size in the first place.
As my design incorporated ash box below the firebox and experimental opening in the firebox floor, I cut a cast iron hearth grid to fit into the opening.. This way I am able to get some 72cm2 combustion air in to the firebox, but from below. Now rocket starts in couple of minutes and I don't have to open the firebox door until the next fire. Fire burns brightly but not out of control. As a bonus, the duration of the ember phase now takes maybe three times less than with door fed over-air and all the embers transform to very fine ash, which readily falls in to the ash pit below. This allows me to close air inlets quicker to maximise the heat retention. The door vents are now working through a deflector plate which guides the door air only upwards through 2-3mm slit to wash the window and ease the thermal stress for the door. Not surprisingly I found it essential not to let anymore air through the door when operating by under-air. Floor channel also takes its air from below before its 25cm horizontal part transports it to the vertical part and for the port. I get to the full burn quickest when lighting the fire in dead middle of the firebox/ fuel and keeping door open and under-air closed for 2-3 minutes in the beginning before switching them around.
I found one thread about under-air here on forums earlier, but of course cannot find it anymore... It was not too long anyway. Also Pyromasse had a clear and straight to the point article about above- and below-fed combustion air: firing.
I am aware that below fed combustion is deemed dirtier and less controllable. Especially this is apparent in the lighting phase. However, the fire in my heater is not wild, there is no flame coming out from riser and smoke from the chimney is white and has the characteristics of vaporizing steam. Smelling the chimney outlet gives a hint of little smoke smell though when my sauna's RMH hardly has any smoke smell in the exhaust. Gotta get Testo one day...
I am not too keen to enlarge the air inlet in the door more as it would start to lose its structural integrity soon, although I am relatively sure it would enable the over-air operation as per originally designed. Also the iron grid with ash pit is really really handy, not to mention the more sealed door as my 2- years old is running around.
My heater's ISA is quite large, near 7m2 because of the oven, which gives me relatively low stack temps; 60'C at hottest when bypass is not employed. I wonder if that combined to narrower than expected chimney stack will cause the need for bigger air inlet... maybe that would also explain why my fire is not too wild despite the below fed air and why the rocket works smoothly?
In the middle of the burn
My questions:
- Any ideas about what could cause the need for that much larger air inlet?
- Would you consider under air burning uncleaner also AFTER the ignition/ starting phase, when the major burn is on?
- What would you estimate to be the detrimental effects in relation to the clean burn and rocket operation?
- I remember (if correctly...) Peter saying in that other thread that the riser would not be able to cope with the under- air setup. What would be the indicators if that is the case? My rocket sound is clearly audible and steady...
Only one oddity/ problem remains: The system requires much more combustion air (ca. 35% of CSA) than estimated 25% of CSA/ about 40+10cm2
For background: donkey32.proboards.com/thread/2308/brick-sidewinder-riser-baking-oven
SKP: design
First the channels in cast iron door were enlarged to be bit larger than the desired air intake size, about 53cm2. This was not enough to let the fire burn briskly and the rocket sound to get started. However everything was fine if door remained bit open. Bit later when the chimney damper was installed, it was found that actually the chimney stack is about 8% narrower near the ceiling compared to its 160x160mm diameter elsewhere, Which I let to dictate my system size in the first place.
As my design incorporated ash box below the firebox and experimental opening in the firebox floor, I cut a cast iron hearth grid to fit into the opening.. This way I am able to get some 72cm2 combustion air in to the firebox, but from below. Now rocket starts in couple of minutes and I don't have to open the firebox door until the next fire. Fire burns brightly but not out of control. As a bonus, the duration of the ember phase now takes maybe three times less than with door fed over-air and all the embers transform to very fine ash, which readily falls in to the ash pit below. This allows me to close air inlets quicker to maximise the heat retention. The door vents are now working through a deflector plate which guides the door air only upwards through 2-3mm slit to wash the window and ease the thermal stress for the door. Not surprisingly I found it essential not to let anymore air through the door when operating by under-air. Floor channel also takes its air from below before its 25cm horizontal part transports it to the vertical part and for the port. I get to the full burn quickest when lighting the fire in dead middle of the firebox/ fuel and keeping door open and under-air closed for 2-3 minutes in the beginning before switching them around.
I found one thread about under-air here on forums earlier, but of course cannot find it anymore... It was not too long anyway. Also Pyromasse had a clear and straight to the point article about above- and below-fed combustion air: firing.
I am aware that below fed combustion is deemed dirtier and less controllable. Especially this is apparent in the lighting phase. However, the fire in my heater is not wild, there is no flame coming out from riser and smoke from the chimney is white and has the characteristics of vaporizing steam. Smelling the chimney outlet gives a hint of little smoke smell though when my sauna's RMH hardly has any smoke smell in the exhaust. Gotta get Testo one day...
I am not too keen to enlarge the air inlet in the door more as it would start to lose its structural integrity soon, although I am relatively sure it would enable the over-air operation as per originally designed. Also the iron grid with ash pit is really really handy, not to mention the more sealed door as my 2- years old is running around.
My heater's ISA is quite large, near 7m2 because of the oven, which gives me relatively low stack temps; 60'C at hottest when bypass is not employed. I wonder if that combined to narrower than expected chimney stack will cause the need for bigger air inlet... maybe that would also explain why my fire is not too wild despite the below fed air and why the rocket works smoothly?
In the middle of the burn
My questions:
- Any ideas about what could cause the need for that much larger air inlet?
- Would you consider under air burning uncleaner also AFTER the ignition/ starting phase, when the major burn is on?
- What would you estimate to be the detrimental effects in relation to the clean burn and rocket operation?
- I remember (if correctly...) Peter saying in that other thread that the riser would not be able to cope with the under- air setup. What would be the indicators if that is the case? My rocket sound is clearly audible and steady...