Rsf Opel 2 secondary air modification
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I have my primary air set at exactly .06 gap, in the fully closed position. Last night I was sitting there watching the fire I had it dampered completely down at like 400 dehg There was a very small amount of primary flame coming off the wood the rest was all from the secondaries . The stove was slowly heating up until it hit about 500 degrees. At this point the little bit of primary air that was coming in started igniting up near the top of the window near the air wash. In turn it was taking away from the secondary flames. At this point there was no flame coming off the wood at all. This went on for about 45 minutes till the stove reached about 520. I was watching it go back and forth it was wanting to burn one way or the other. either with my secondary air or with the little bit of primary are coming in but burning before it hits the wood. It starts fighting back and forth with each other until eventually it just completely goes out. I went down and open the damper to get the flames going again. And boom I got a big backfire that made my doors clap . So I put my bigger Shim back in the air supply and went to bed.
At this point I don't know if it's getting too much secondary air or what I can fix the issue by supplying more primary air but then my wood burns too fast. I think after work I'm going to try putting the factory secondary are burner back in the stove fill it up and see how it works now with the baffle plate.
My question...
Is there some sort of safety protocol when your flame dies out with a really hot stove? When this happens I typically open and close the primary air damper real quick. I Do that a few times till it lights. As soon as it lights I try to quicky open the primary air wide open .... Would it be better to open it widen open and leave it till it relights to avoid a big boom or is that worse ???
At this point I don't know if it's getting too much secondary air or what I can fix the issue by supplying more primary air but then my wood burns too fast. I think after work I'm going to try putting the factory secondary are burner back in the stove fill it up and see how it works now with the baffle plate.
My question...
Is there some sort of safety protocol when your flame dies out with a really hot stove? When this happens I typically open and close the primary air damper real quick. I Do that a few times till it lights. As soon as it lights I try to quicky open the primary air wide open .... Would it be better to open it widen open and leave it till it relights to avoid a big boom or is that worse ???
Normally, when burning dry wood, the flame dies out after all the wood gases are spent. Then the fire goes into the coaling stage. This can last many hours, depending on the firebox capacity and the air that the fire receives. If the flame is going out before the wood has burned up all the volatiles then it probably is not getting enough primary air or the wood is not fully seasoned.
I came down to that conclusion. Not enough primary air. A little more primary air burns the wood to fast. Could it be that I have way to much air coming out of my secondary burner? Again any safety protocol I should fallow when this happens?
The main thing is to not let the fire smolder and fill up the firebox with smoke and wood gases. When these gases reignite the result can be dynamic.
This is a one-off variation of a stove that no one but you has burned in. Hard to say what will make it burn the best. That will take experimentation and perhaps some adjustments to the system.
Too much secondary air for the tube design you are using. But the below is based on your written descriptions as your video is now offline.
I've spent a significant amount of time adjusting the secondary burn of my stove. My stove is EPA 2015 rated for a 15ft chimney, mines 36ft tall creating about 3 times the draft the stove was designed for. With a full load of wood and the damper shut there were times the flue temps were bouncing around the 900F mark on the probe thermometer. My damper solely controls primary air like most tube stoves, the secondary air is wide open all the time, at some point there becomes so much secondary air it becomes turbulent and acts as additional primary air, creating a run away condition within the firebox. During this stage the wood burns down rapidly to coals, at which point the whole process almost stops. The secondary air doesn't seem to reach far enough down in the firebox to help burn the coals and with the primary already shut the coals have a hard time burning completely down to ash.
My solution to this is rather simple, I use a 1/4" finishing washer pressed into both ends of all my tubes, I then drill out the inside of the washer so the area of the holes is 70%-95% of the area of all of the holes in the tube combined. This washer in the tubes act like an orfice and limit the amount of air going through the secondary system. Using this method takes a bit of experimentation to get right, going from say 70% to 90% is a huge difference, as both the holes in the tube and orfice washer are working in conjunction to limit the airflow. I can now happily report that I can easily keep the flue temps around 500F with a full load, I burn less wood, and the wood burns longer.
I believe you could run a similar setup inside your 1.25" tube to limit airflow, I'm not sure you'd be able to find a washer big enough, but by the looks of things you should be able to fab up some kind of orfice to put inside.
Now for the hard part, the design. My stove and most tube stoves have the holes in the tubes pointing forward, this pushes the gases in the firebox forward toward the opening in the baffle and out of the stove, like in my experience though enough air causes turbulence and acts as primary air. Your design is sideways and pushes the gases to the middle, eventually these will converge in the middle of the stove and with nowhere else to go will be forced down onto the wood, also acting as primary air, causing the rapid burn down of the wood with coals leftover. I believe this will also contribute to your flame burning to one side or the other.
Honestly I don't believe you have too much secondary air, 60 5/32" holes is 75% of the hole area my tubes have, I believe the design is as least as much a part of it, but choking down the secondary air is a far easier test to complete, and that's where I would start. It is possible that you may still attain satisfactory results by limiting the velocity of the air out of the tubes and reducing the converging effect.
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AB thank you!
I can very easily lathe some insterts for the tube main tube. I just counted and I actually have 89 holes. I will have to do some math and see where I should start when simply x 5/32 by 90 that is over 13 inches
I was also confused if my main pipe has an inner diameter of 1.123 . It is also fed at both ends
The actual smaller burner tubes have an ID of 1/2"
Is there anyway you could tell me what size whole to start with on each end of my main pipes insterts?
Yup that's easy, I have an Excel sheet for mine.
90 5/32" holes gives you a total hole area of 1.72 sqin.
Assuming you make an identical orfice for each side you'd need the following holes in each:
95% 1.02" diameter
90% 0.99" diameter
85% 0.96" diameter
80% 0.94" diameter
75% 0.91" diameter
70% 0.88" diameter
65% 0.84" diameter
60% 0.81" diameter
55% 0.78" diameter
50% 0.74" diameter
I think you might want to start around 80%, that being said though it's easier to machine the hole larger if it's too small, if it's too big you start over, so you might want to start at 60% and go up. For my stove I've never went smaller than 65%, and that was too small for my application, but yours will be different.
Let us know how it works out.
One thing to note is 5/32" holes are quite large for secondary tubes. In the case of your center tubes the 30 5/32" holes have 3 times the opening of the 1/2" ID tubing itself (ie can flow 3 times more air than the 1/2" tube can supply to them), currently the amount of air is mostly being limited by the tube diameter, as such the outside tubes with 15 holes will have a far higher air exit velocity than the center 2, as there are less holes sharing the flow from the 1/2". Your 1-1/2" tube is sufficient for 90 5/32" holes however.
Every stove tube I've looked at always has the holes as the choke point for the secondary system. Part of this is because they are fed from both ends instead of one. Every other component in the system is capable of flowing more air, using the holes as the restriction for volume control, something to consider should you end up building another version of this.
Every stove tube I've looked at always has the holes as the choke point for the secondary system. Part of this is because they are fed from both ends instead of one. Every other component in the system is capable of flowing more air, using the holes as the restriction for volume control, something to consider should you end up building another version of this.
I definitely want to design another burner this one was simple and quick. very thankful for you to spinkle me with some knowledge. Do you think blocking off every other hole would be a good idea ? If so , Would I just divide all your orfice dia calculations in half?
You could try it, some say less but larger holes are better, as opposed to the "shotgun" approach of lots of small holes.
No, it's calculating area which is a squared function. If you go with 45 5/32" holes instead of 90 divide all my numbers by 1.414, that will give you the correct orfice diameters. For example 95% becomes 0.72" diameter.
If you get really far into this I can send you a modified version of my excel sheet to use.
Thanks for all the info ABMax24 ! So if i had 30 3/16'' holes would that be .84 sqin ?
Also in your opinion do you think the "shotgun" smaller holes approach is better than the larger holes?
Also in your opinion do you think the "shotgun" smaller holes approach is better than the larger holes?
I get 0.83 sqin, but yes.
That I can't guarantee either way, it was something I read on here from another member that had done some modelling in CFD. My experience was less about number and size of holes and more about total air volume. What I do know is there piles of tube stoves out there that have passed EPA 2020 using the "shotgun" effect. Best I could say is try both and decide for yourself which is best.
That I can't guarantee either way, it was something I read on here from another member that had done some modelling in CFD. My experience was less about number and size of holes and more about total air volume. What I do know is there piles of tube stoves out there that have passed EPA 2020 using the "shotgun" effect. Best I could say is try both and decide for yourself which is best.
Are your percents or decimal inch numbers rounded? Looking closer I would think as the holes get larger the diameter increments would get smaller to hold the same volume??? I'm no engineer...
I'm not an expert on this by any means but IMO that looks like one of three things:
1. The primary air is cut back too far and the stove stalls
2. The stove was turned down too soon before enough wood gases were being evolved to support secondary combustion
3. Wet wood
1. The primary air is cut back too far and the stove stalls
2. The stove was turned down too soon before enough wood gases were being evolved to support secondary combustion
3. Wet wood
Possibly Not enough air.. I was running a .06 gap in my primary air during that video. Last night completely removed the secondary air out of the equation for a test. I had to actually run a .100 gap in the intake to even get it to some what burn. It was on the edge the whole burn. With this .100 shim I only get about 8 hr burn times. If I drop to a .06 I could see about 10 hrs. .03 I see about 12hours. The whole reason I'm doing this is to extend burn times. Ideally I would like to be able to run a .03-.06 gap so I get 10-12 hr burns . Is it true that by adding secondary air I can close the primary air much farther than without secondary air and still get a decent burn?? It seems that way to me and I may need to just slow down the secondary air supply so it doesn't go into over burn as you were saying.
When you added secondary air your stove were you able to close the primary air alot more? If so Did it increase burn times? What temperature do you wait for (stove top temp) before you close the primary down?
1/2 my wood is not bone dry but well seasoned no bark. I really need to pick up a moisture meter
My stove came with secondary air, so I really can't help you there. I haven't even operated a stove without secondary air in the last 18 years.
It really depends on what your definition of a 10-12hr burn is, with my stove after 10hrs I really only have a small shovel scoop of glowing coals left in and amongst the ashes. The bulk of the heat with mine is already released by the 6 hr mark. A lot of stoves with secondary air the size of yours are only quoting 10hr burn times as well, 12 hrs is a pretty big stretch for a non cat stove. A big reason for this is emissions, you need to burn enough fuel to keep the firebox hot enough to continue with the secondary burn. A long smoldering fire isn't good for creosote buildup, efficiency, or particulate emissions. The only way I know how to reliably stretch burn times to 12hrs or more is to buy a catalytic stove built specifically for that purpose.
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