[Stoves] Nozzles for TLUDs Re: venturi system -ratios of air and gas?

[alex english]

Julien,
You can pre mix with a ND- TLUD but you need some chimney to power it. I
have used a 2 inch sch 40 pipe. It becomes a chimney to pull primary air
through the fuel. Add secondary air near the top then widen out to a larger
pipe for combustion. Depending on the mix the flame will be either close to
the bottom of the widening point or further up. Again, depending on the
mix, it will either have an orange top or be blue/purple. It hasn't flashed
down the 2" tube. Its do-able but for practicality I prefer Roberto's
approach.
Alex

On Mon, Jan 11, 2016 at 12:54 PM, Julien Winter <winter.julien at gmail.com>
wrote:

> Hi Paul, Frans and all;
>
> When you talk of Kevin Adair's nozzle, are I assume you describing a
> hourglass riser above the concentrator ring?  Something like the hourglass
> comes to mind following Frans' comments on the coanda effect.  However, I
> expect that the dominant force at the bottom of the hourglass would be
> buoyancy, straight up.
>
> A rough type of 'hourglass' venturi burner was invented by Dave Yarrow
> (ca. 2013) for barrel type TLUDs.  I built one myself, and it roars.  I
> have attached a couple of photos
>
> 1) shows the whole unit.  There is a 130 L reactor barrel inside the 200 L
> barrel, so secondary air was being preheated, and passed over the top of
> the 130 L barrel where woodgas ignited under the concentrator.  The flame
> then went up into the chimney burner.
>
> 2) shows the bottom of the chimney burner, which constricts to accelerate
> the gases, then expands.  Where it expands, there are tertiary air holes
> that are cut at an angle to get rotational turbulence (supposedly).  The
> idea is to create a bit of a venturi suction for the tertiary air.
>
> This unit is designed for a high gasification rate.  At low gasification
> rates, the flame is below the concentrator.  I haven't done any more work
> on this idea, because I have been focusing attention at on the initial
> mixing of woodgas and secondary air.  I have yet to move upstream.
>
> I don't have this unit any more.  I gave it to a friend who lives in the
> countryside, and does not fear being shut down by the town's fire
> department.
>
>
>
> Of course, anything said about a natural draft, wood gas burner is
> dependent on the supply rate of woodgas, because that can change its mode
> of operation (as above).  The big problem for any burner is to get it to
> work over a wide range of woodgas supply rates.  What works great at a
> medium gasification rate, can be the cause of smoke at a high gasification
> rate.
>
> Premixing air and woodgas under natural draft would be a nice thing to
> achieve.  The challenge under natural draft is to get the flow of the
> mixture to be faster than the flame speed of H2, CO, CH4, so there is no
> flash back.  We may be able to achieve that at higher gasification rates.
> At low rates, the flame will likely flash back to the top of the char,
> which may not be a bad thing for low turndown.
>
> Cheers,
> Julien.
>
>
>
> --
> Julien Winter
> Cobourg, ON, CANADA
>
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