[Stoves] Down with Fantasy-draft stoves

Mon Jun 18 00:18:23 CDT 2018

Alex,

This is a pot with some kind of open-burning stove inside it.  The air is entering the pot at the top but can enter the stove at the bottom or sides.  I question if this stove is a TLUD.   If it has a MPF and the gasses are being burned separately in a secondary flame with air supplied by the side holes, than it may be operating as a TLUD.  There are no gas flames at the top of the stove where the wood gas would mix with air coming over the top, as a TLUD would usually operate.  The flames are burning before they exit the chamber so my guess is that it is an open fire.

I did some experiments on turn-down several years ago, directing some air downward in the reactor chamber.  It turned inward when it reached the top of the char and burned the wood gas as it rose out of the char, giving excellent turn-down.  I did not see it penetrate below the surface of the char let alone the MPF.  Also as the char level dropped during the burn, the air had to travel further downward to reach the surface.  It was heated by the fire as it descended and became buoyant, turning inward before reaching the char, so the flame was separate above the char.  It did still worked for turn-down.  Hypothetical primary air entering from above would probably do the same, heat as it descended, become buoyant, and not reach the top of the char.

Kirk H.

Sent from Mail for Windows 10

From: alex english
Sent: Sunday, June 17, 2018 2:24 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Down with Fantasy-draft stoves

Hi Stovies,

This relates to Paul's doubts that all the air can come in the top of a TLUD.

I took two off the shelf items and with no alterations and made a serviceable stove for wood pellet fuel . I placed a stainless holey cutlery strainer on a shim in the bottom of a small stainless milk pail. The strainer is 4 5/8 inches in diameter and 5 inches tall. The top was about 3/4 of an inch below the top of the pail. Half filled with pellets, which leaves the pellets 3.5 inches the below the pot.  Top lit, it burned for about 45 minutes with all the air coming in from the top. The migrating front headed 'south' predictably. A little ash formed around the edges. Good flame stability.

It is basically a one speed device unless you manipulate the fuel profile. 
The pot position, size and shape is a factor as the exhaust and air pass by each other in close proximity going in opposite directions.

A pretty simple stove. 

Alex 

On Thu, Mar 29, 2018 at 8:39 AM, Paul Anderson <psanders at ilstu.edu> wrote:
Alex (and others)

You wrote:
That primary air  can be introduced above the fuel with the secondary air
and drop down and spread out below the
pyrolysis front.
  I would certainly like to see this demonstrated (visible) or supported by scientific measurements.  Frankly, I have my doubts, especially if it is less than 20 cm (8 inches) in diameter..

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com

On 3/29/2018 5:40 AM, Andrew Heggie wrote:
On 29 March 2018 at 01:32, alex english <aenglish444 at gmail.com> wrote:
Andrew,
If you are curious you can 'freeze' theTLUD process at any point by setting
the a TLUD in a pan of water that shuts off the air and wicks water into the
raw pellets in the bottom of the fuel chamber. They will swell and wick all
the way up to the Migrating Pyrolysis Front . The Torrefied layer and the
char above will not swell. A careful excavation of the fuel will reveal all.
When I did  this with the 18 inch diameter chamber I found a horizontal
layer of an inch, or a bit  less, of pellets in transition from raw pellet
to torrified pellet to charred pellet.
Thanks again Alex it's an interesting experiment but I'm quite happy
to take your word for the horizontal MPF.

   Misting the outside of the stove
will can also give clear impression of a planar descent of the  MPF.
I never did much with pellets as I felt they were not a likely fuel
compared with stickwood and so not representative of most users  In UK
I find them too expensive compared with other fuels.
With very dry fuel like wood  pellet very little primary air is required.
That primary air  can be introduced above the fuel with the secondary air
and drop down and spread out below the
pyrolysis front.  If introduced tangentially the cooler fresh air
centrifuges to the outside edge of a round chamber and the flame tornados up
the middle. A layer of fresh air one millimeter thick descending around the
edge of a fuel chamber would be enough. Not a lot of control but this
resembles what many people have used this sort in other contexts. With
fussy fuel quality and placement it behaves in the steady top down way that
a TLUD does with a little extra char burning.
Yes I made many such vortex burners in my experiments, the largest
being 4foot diameter but I supplied all the air from above and
inevitably to excess.

Andrew

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