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Front to back tube burner for secondary air?

 
pollinator
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I was in my local BBQ shop today looking for a portable (cheap) BBQ to take the coals left over from my burns, and I saw this thing

https://www.amazon.com/GrillPro-21218-Universal-Front-Burner/dp/B0027EGNTE



They appear to be cheap disposable SS tubes for taking gas to a fire.  So, could they be used for bringing in fresh air to the Venturi?  I know that the preference is for superheated air to be brought to the port but how much difference does that really make when you're talking about 800 deg C in your firebox?  I was just thinking of dropping in down from the top of the batchbox before the Venturi but not lying it against the top of the firebox as in the P channel.

 
Graham Chiu
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I just stumbled upon this link from JUCA stoves http://mb-soft.com/juca/print/315.html

Can someone confirm how valid this analysis is, and its application to batch boxes which operate in an air starved environment?  Secondary air requirements give this extra burden of providing a piece of stainless steel that one needs to keep renewing.  How much better does it really improve the burn by?
 
pollinator
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I am no expert but I think that a rocket stove works extreamly well when fed secondly air, it needs to be very hot air and the area it feeds must also be extreamly hot.
There are a few vids that show it working, Potty has one and he talks you through it too.

The thing is there are no rocket stove police so you can do what you want and as you have proved you don’t need to follow protocol to enjoy messing with rocket fires however ... I think to get the very best results ... a sealed unit with controlled air feeds allows much more scope to get the best from your fire.
I also think that a lot of the designs are about getting a very clean exhaust, not just a smoke free effect.
I am not even sure what type of fire that articles is talking about?
 
Graham Chiu
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The JUCA stove seems to be a very old design.  I think it's a very large firebox with lots of air using a forced blower and massive heat exchangers to get the heat out.  I'm guessing it's the size of the fire that allows them to burn as clean as they say, and because it's not air tight, and has a lot of air being brought to the fire they are exempted from the EPA regulations.

However, they look somewhat ugly and in tune with that their website still has a retro 1970s look about it.  See https://www.farmshow.com/a_article.php?aid=2981 for a picture of one of their wood furnaces.

Anyway, I was probably thinking of how much air is actually delivered by the Venturi effect, and how much heating can the air get if the pipe is sitting on top of the firebox made from firebrick?  I've measured the temperature of the exterior of my firebox, made of firebrick, and it might occasionally exceed 100 deg C when the interior is 800 deg C.  So, that's not going to superheat the secondary air coming into the firebox, is it?
 
Fox James
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You are baseing your observations on your own design, perhaps a sealed batch rocket with a door and cement between the bricks and an insulated heat riser would heat up more?
Maybe it would be worth while considering how to pre heat the air rather than not using it at all.
Perhaps whole fire brick is not the best way to form the fire box top or you could have the steel tube inside the fire box or set in the floor....
 
Graham Chiu
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Hi Fox

I was asking about the p-channel as shown here http://batchrocket.eu/en/designs#brick1

The roof of the firebox is made of brick and the secondary air channel is lying on top of the bricks before diving into the firebox opening at the Venturi.
I can see how the floor channel is providing preheated air, just not seeing how the p-channel is though.
 
Fox James
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I know what you are saying, most batch rockets seem to use a cast top that is not 3” thick though.
I do agree that it would take a long time to heat up a full size brick even covered in insulation!
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