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Post by smokeout on Jan 4, 2018 23:35:25 GMT -8
I do have a p channel for secondary air. I'm getting highest temperatures without it though. I'm thinking the small amount of wood I have burning has it running lean already. The stove still gets blistering hot without secondary air. As soon as I introduce the smallest amount of secondary air, I can detect a temp drop with ir sensor.i If I load the feed tube all I can get in it, then I can get the secondary air to bring up the temperature .
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Post by Vortex on Jan 5, 2018 3:08:10 GMT -8
Is this a batchbox with rear port and riser or some other configuration?
Pulsing is apparently caused by a restriction downstream - which would be true as you said the flu goes down from a 8" to 5" before it exits the house - The cold primary air enters the stove and when it hits the hot fire expands 4 times in volume, if there is a restriction to the gas flow somewhere in the system it creates a bounce back that momentarily halts the incoming primary air, or even reverses the flow until the gases start to move through the system again, this effect repeats quite fast making a chuffing sound like an old steam train.
I always find closing the primary air down slightly until the pulsing stops sorts the problem.
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Post by pinhead on Jan 5, 2018 5:40:44 GMT -8
As soon as the riser gets enough heat to start drawing fire, the pulsating stops. It happens only on start up. This makes sense. In my experience, pulsing is caused by "flashover" and "backdraft" much like in a house fire. The heat in the riser is approaching the temperature at which the volatiles in the riser spontaneously and simultaneously combust, causing a spike in pressure. At this point, all of the combustibles in the riser are consumed until it fills up again, at which time it will again ignite and pulse. Depending on the size of the riser, temperature, air speed, etc. will determine the frequency of the pulsing. I've seen it chuff about every second or so, and I've seen it run like a pulse jet engine. IMHO this can be caused by a number of factors. The first problem could be a riser with too much mass or a riser made of some material that is able to spread the heat across its surface. The second problem could be a restriction down-stream that doesn't allow the hot gasses to flow through the riser quickly enough to prevent autocombustion.
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Post by smokeout on Jan 5, 2018 7:26:25 GMT -8
Pinhead and Vortex, I think both of you have shead some light on why she flashes back on me. This is my reasoning behind the 5" flue pipe. I have 13' of 5" double wall vertical flue pipe. I used the double wall going out of the heated space to conserve as much heat as possible, plus the smaller pipe takes away the extra space created by the cooling gases. The big thing that got me onboard with smaller pipe was this, I pulled my exhaust pipe to check on how clean the stove was burning. To my surprise the the air was just creeping out of the stove. The next topic is probably my biggest cause. When I built the stove, I placed the feed tube as close as possible to th heat exchanger, but that still had my horizontal tube longer than it should be . By observation, I can see when flashback occurs. Just as my tunnel fire gets going enough to pull fire to the vertical riser, it flashes back. On my next build, I will consider offsetting the riser in the heat exchanger to help that situation. This begs another question that I've had on my mind. Is it possible that I can get away using a batch box heater and the same feed tube sitting on top of it? I'm looking to have two options on burning wood.
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Post by matthewwalker on Jan 5, 2018 8:40:18 GMT -8
I built one like that a long time ago, batch with closeable top feed. It worked pretty well, I would say that although it's a bit of a compromise in both, it does work.
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Post by smokeout on Jan 5, 2018 9:20:32 GMT -8
Is this a batchbox with rear port and riser or some other configuration? Pulsing is apparently caused by a restriction downstream - which would be true as you said the flu goes down from a 8" to 5" before it exits the house - The cold primary air enters the stove and when it hits the hot fire expands 4 times in volume, if there is a restriction to the gas flow somewhere in the system it creates a bounce back that momentarily halts the incoming primary air, or even reverses the flow until the gases start to move through the system again, this effect repeats quite fast making a chuffing sound like an old steam train. I always find closing the primary air down slightly until the pulsing stops sorts the problem. Sorry Vortex , I missed your question. It's a standard j tube configuration with a sealable 50" feed tube.
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Post by smokeout on Jan 5, 2018 9:51:54 GMT -8
I have made one modification. The horizontal tunnel is 6"x8". Once I get the tunnel fire going on start up, I place a a reducer in the tunnel up to where the fire burns thus forcing the air to flow through a 2"x6 area. This seems to intensify the burn and it prevents ash and coals from migrating towards the tunnel door. I then close the door and load the vertical tube . It drafts so well that I can have the tunnel door and feed tube door open at the same time with no problems. This isn't possible once the stove comes up to temperature, but I can open the feed tube door anytime as long as I have the primary air restricted somewhat. I built two channels for the primary air that are 1" wide and 11" tall . The air enters on both sides of the horizontal tunnel and go towards the rear of the stove almost to the riser. They then turn 180 degrees and come back to the front of the stove and enter on the sides and top of the tunnel. The secondary air tube works quite the same way. There is only one, it enters along the front and bottom of the burn tunnel goes back to the riser and splits up both sides and then merges back together on top of the horizontal tunnel before entering the riser. The insulation and primary air tubes do a great job at keeping the heat in the tunnel. My stove has been running for three hours and the outside of the stove directly adjacent to the burn tunnel is 55F.
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Post by Orange on Jan 6, 2018 12:27:15 GMT -8
Orange, how hot is your radiator when burning? When you have experienced pulsing what did you find upon measuring CO or efficiency? smokeout has a pulser, not me my idea was when the chimney temp is around 60C to put shortly a cheap plastic CO sensor in to see how much ppm of CO there is, which would tell if it burns clean or not. Like primitive Testo
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Post by satamax on Jan 6, 2018 12:41:53 GMT -8
One tell tale sign of a clean burn, the chimney cap which stays clean after few heating seasons.
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Post by matthewwalker on Jan 6, 2018 13:11:42 GMT -8
Orange, how hot is your radiator when burning? When you have experienced pulsing what did you find upon measuring CO or efficiency? smokeout has a pulser, not me my idea was when the chimney temp is around 60C to put shortly a cheap plastic CO sensor in to see how much ppm of CO there is, which would tell if it burns clean or not. Like primitive Testo So you were speculating that this completed build was not performing well based on zero experience, making the OP doubt their build? Orange, I HATE calling you out. It sucks for everyone. Please, please, please, before you comment, stop and think for a moment. Ask yourself, "do I have any experience here?". "Does this help the conversation or cause confusion or doubt?" Please try harder to do these things, it will make the board better for everyone.
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Post by Orange on Jan 8, 2018 12:56:45 GMT -8
Matt, we're all speculating here. I hope you're right and that high temps are a result of a clean burn but I experessed concern with the pulser and the lack of CO data. I guess for this forum definition of "clean burn" is <500ppm CO?
So to make it simple, "clean burn" is when the stove is getting >900C inside, >400C outside + chimney cap which stays clean after few heating seasons + only white smoke during burn.
"Super clean burn" is the above stove + <500ppm CO at 13% O2.
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Post by matthewwalker on Jan 8, 2018 13:09:54 GMT -8
Orange, again, you have zero experience, yet you cast doubt on someone's build. They have no idea that you have never had a rocket, so they may consider you an experienced hand and doubt themselves. Here's the thing, those of us with rockets know that if you are achieving 900 on the barrel you have a very good stove. That's my point, not any of the numbers you have read about. Again, please just stop with these speculations on others' builds. You are not adding to the conversation, but rather creating a situation where I feel the need to correct you to reassure the OP. I could stay out, but then we just have more confusion and bad intel cluttering the board and confusing people. I'll say it again, ask yourself if you are helping OP or just adding doubt and speculation. Ask yourself if you have any experience. Better yet, just read along for a while until you get some experience, or have a question regarding your own build.
It really sucks calling you out, but we are trying to help people here, and beginners guessing isn't helping. No offense.
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Post by smokeout on Jan 10, 2018 6:50:00 GMT -8
I decided to make some changes again. I have been using 1" duraboard inside my 8" stainless steel riser, but only half way up. I was still getting some spalling, so I relined the riser all the way up. So effectively now I have a 6" dia 48" riser. I'm am totally shocked at how much faster the stove comes up to temperature and the heat exchanger is getting hotter too . It's holding steady at just over 1000F . I will refuel and see how long it can run on a fill up. youtu.be/EGM7YBSu2JY
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Post by pinhead on Jan 10, 2018 7:03:33 GMT -8
I decided to make some changes again. I have been using 1" duraboard inside my 8" stainless steel riser, but only half way up. I was still getting some spalling, so I relined the riser all the way up. So effectively now I have a 6" dia 48" riser. I'm am totally shocked at how much faster the stove comes up to temperature and the heat exchanger is getting hotter too . It's holding steady at just over 1000F . I will refuel and see how long it can run on a fill up. youtu.be/EGM7YBSu2JYThis is exactly my experience and is why I'm leery of using a shortened riser as in the case of a cook stove. Every stove I've ever built has benefited dramatically from a taller riser. I'd like to see all Batch Boxes stick to the dimensions (including riser height) and if something shorter is needed, either don't call it a Batch Box or use the DSR. Sorry for the thread hijack. Good work and post a burn video!
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Post by smokeout on Jan 10, 2018 7:49:14 GMT -8
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