[Stoves] Reports from ETHOS meetings: the future of TLUD research

[alex english]

Julien,
Agreed. Its been a twenty year wait for basic in depth research on  natural
draft TLUDs.
Natural draft mixing was my passion for a while. I think "natural draft" is
still too broad a term. There is a dramatic difference in gas mixing
potential of  30, 90 cm of buoyancy.
It will be interesting to see the results shared, but I am inclined to
think the money would be better spent putting portable combustion gas
analysers in the hands of folks like you and Harris.

My excess air for today,

Alex

On Wed, Jan 28, 2015 at 12:45 PM, Julien Winter <winter.julien at gmail.com>
wrote:

> I was at ETHOS this year presenting some of my basic investigations of
> TLUD function, and I will circulate a copy of my presentation shortly.
> Kirk Harris presented his fascinating burner design.
>
> For me, one of the most interesting things at ETHOS was not what was
> presented, but what is coming.  The Colorado State University has received
> a very large grant from the US Department of Energy to improve our
> scientific understanding of natural draft TLUDs.  This year at ETHOS, they
> didn't present any results, but they described the laboratory equipment
> that they have assembled.  They will be able to measure the flow rates of
> primary and secondary air, fuel bed and gas flame temperatures, gas flame
> structure, the composition of the pyrogas as it exists the fuel bed, and
> exhaust gas and particulate emissions.  They are able to test a variety of
> gas burners to increase clean-burning --- the most pressing issue today.
> Knowledge gained on pyrolysis, combustion, and gas flows will be
> systematized into computer simulation models.
>
> This work is much needed.  Since the early 1980s, forced draft systems
> have been extensively studied, however, except for a couple of recent
> papers, natural draft systems, have not been studied at all.  Research on
> forced draft has provided us with some very important information, but it
> doesn't extrapolate sufficiently well to natural draft systems.    Natural
> draft systems different from forced draft systems, in three basic
> ways: (1) they operate at lower gas velocities, near atmospheric pressure,
> (2) operational temperatures cover a lower range, and (3) and their
> processes, are interconnected through feed-back mechanisms.  We have to
> understand how these feedbacks work for designing ND-TLUD stoves.  For
> example, how does the size and shape of the pyrogas flame affect draft for
> primary air --> gasification rate --> size and shape of the pyrogas flame
> --> ...
>
> It will be interesting to see what the workers at Colorado State
> University come up with.  I expect they will be able to tell us what the
> control or limiting points are in the TLUD reaction, such as resistance to
> gas flow in the fuel bed, or heat production at the pyrolytic front.  They
> should be able to tell us how the thickness and temperature of the char
> layer above the pyrolytic front changes the composition of pyrogas rising
> through it.  They should be able to tell us how the composition of pyrogas
> changes over a turndown curve.   Most importantly, I hope they will provide
> guidelines for designing burners, reasons for why one thing works and not
> another, and a computer program to simulate design decisions.
>
> The results from the Colorado State University lab can't come too soon.
>
> Cheers,
> Julien.
>
> ---------------------
>
>
> --
> Julien Winter
> Cobourg, ON, CANADA
>
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