[Stoves] Cross-Current Woodgas Burner with Air Inlet Tubes Angled 45° Downwards - YouTube Vid

[Jock Gill]

Julien,

I. Love your videos.  I also note you are using a 30 gallon trash can as a test environment for your burns.   My iCan in a Trash Can does the same.  This particular iCan design uses three cans, as can be seen in the PDF - available upon request.

I suggest the following:

1. Isolate the pyrolysis gases.  Use a flame retention plate to cover as much of the fuel bed as possible to prevent as nearly as possible any O2 from reaching the fuel bed.  This will also isolate the burning gases such that they can be dealt with more nearly without interactions with the fuel bed - fewer variables.  I find a flame retention plate that is about 2/3s the radius of the fuel chamber is a good starting point -- if memory serves me well.

2. A retention ring above the secondary air feed makes a lot of sense.

3. Try placing some sort of top on the combustion zone -- I use three washers -- to promote turbulence and allow the maximum time for the secondary air and pyrolysis gases to mix and burn as cleanly as possible - given the non linear fuel/air ratio.  This should also help to keep the burning gases hotter longer.

4. Try to achieve a blue flame - this requires a very nice balance of secondary air to pyrolytic gases.  Since TLUDs are very non linear, the ideal fuel/air ratio is very hard to maintain.  I find that if I limit the primary air to the least amount required to start and sustain the first 10 minutes of a run, I can get some blue flames.  As the unit heats up and the pyrolysis front moves closer to the primary air, the power of the draft on the primary air increases, the pyrolysis accelerates, and the fuel/air mix becomes significantly richer.  Consequently, you have to look at the flame and emissions over the entire pyrolysis period.  Results will vary significantly over time.  A ND TLUD can really only be tuned for the best average performance.

Regards,

Jock


Jock Gill
P.O. Box 3
Peacham,  VT 05862

Cell: (617) 449-8111

google.com/+JockGill

:> Extract CO2 from the atmosphere! <:

Via iPad

> On Jan 27, 2016, at 12:11 PM, Julien Winter <winter.julien at gmail.com> wrote:
> 
> Hi folks;
> 
> I have posted another vid.
> 
> Cross-Current Woodgas Burner with Air Inlet Tubes Angled 45° Downwards 
> 
> https://youtu.be/QmnUgj75TF0
> 
> This video is a brief introduction to work in progress.  The main objective is to design woodgas burners that (1) cause good mixing of air and woodgas over the top of the fuel bed char, or at least at the base of the gas flame; (2) create a flat flame that retains heat, as opposed to a tall conical flame that can cool off at its edges resulting in incomplete combustion (e.g., of soot).
> 
> The burners in this video were designed to give horizontal space for woodgas flame expansion so they are 1.2 to 1.3 times wider than the circumference of the TLUD reactor.  (If they are wider, they produce smoke at low gasification rates.)
> 
> There is an experimental series of five burners with 8, 12, 16, 20, and 24 tubes.  Only the 8 and 20 hole burners are being tested at the moment.   It is expected that the burners with 20 and 24 tubes will be the most efficient, and produce the lowest polluting emissions.  The reason for including burners with fewer tubes is to document the reduction in burner performance as tube number decreases.   If this tubular design is adopted, it is expected that some stove-builders may want to use fewer holes, because the burners will be easier and cheaper to make.  We need to prove why this is a bad idea.
> 
> On the metal burner, there is a narrow deflector ring inside the riser that functions to prevent vertical flamelets going up the riser walls.  Curiously, there can be both a horizontal and vertical flamelet originating from a single air hole.  The vertical flamelets are cooled off by the riser walls, and emit soot.  The deflector ring also prevents unburnt woodgas from escaping up between air holes.   This problem increases as the space between holes increases.   The trials in this video showed that a deflector ring should also be fitted to the burners with tubular air holes.
> 
> The burners with conical tubes are made with cones with edges that radiate out from the central, vertical axis of the burners when tubes are horizontal.   The purpose of the conical shape is to reduce air friction along the sidewalls of the tubes.  The tubes create a laminar flow of air that is pointed inwards, and at a 45° angle downwards.  In the present experiment, the horizontal diameter of tube at the air outlet and the space between outlets is kept the same.  That means that as the number of air tubes decreases, the total area for the ingress of secondary air increases.
> 
> The burners with conical tubes are made of refractory cement (Imperial Manufacturing Group, Richibucto, NB, Canada) and perlite in a 1:2 volume ratio.   The use of perlite is going outside of the manufacturer’s design parameters, and I don’t yet know if this recipe is durable.  The reason for using perlite was to reduce the weight, because the stove will be run on a weight-scale.  A burners weigh about six kilograms.   The surfaces of the burners were coated with refractory cement paste to create smoother surfaces.
> 
> The burners in these videos were sized to work on larger diameter TLUDs (18 cm) burning rough fuel, so the flame structures are coarser than with small TLUDs designed for only pellet fuels.  The present prototypes don’t preheat the secondary air.  They should also be operated out of the wind, because gusts will cause secondary air intake to increase on the windward side.   If burners like these are operated out in the open, the secondary air intakes should be shielded.
> 
> Thanks to Crispin P.-P. for his advice on the “artificial pot” placed on top of the burners’ risers to prevent downdrafting of ambient air.
> 
> Now I need to read over the exellent comments from the previous vid. and reply.
> 
> Cheers,
> Julien.
> 
> 
> -- 
> Julien Winter
> Cobourg, ON, CANADA
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