[Stoves] Studies of pressure variations in a TLUD - Pulsing Flame with Concentrator Rings

[Anderson, Paul]

Julien, Crispin, and  all,

The  pulsing flame is not something that I have  observed, nor ever mentioned to me by Paal Wendelbo or Tom Reed.   Very interesting.   If you can replicate the  pulsing, you can probably determine the factors that impact  it.   Most important is to understand it pulsing has favorable or unfavorable impacts  on the operations of the TLUD-ND (or other) stoves.

Paul

From: Stoves <stoves-bounces at lists.bioenergylists.org> On Behalf Of Crispin Pemberton-Pigott
Sent: Monday, June 22, 2020 9:03 PM
To: Stove Discussion <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] Studies of pressure variations in a TLUD - Pulsing Flame with Concentrator Rings

Dear Julien

What you can try (because it is so easy) is have three holes point left and the fourth point down right, three left, one down right.

You don't really want a vortex. I have used that in the BLDD4 downdraft coal stove patented in South Africa (a deliberately created vortex with a flame burning inside a narrow tube using the less rapidly turning air as an insulator).

Such a flame is greatly extended in length and can be seen in a "firenado" such as those featured in the news from Australia. Look for videos.

The purpose of such an arrangement is to be able to reduce the excess air to 35% or so and still get perfect combustion. Or darn near it. It was also used in the BLDD6.

The flame was spinning inside a 50 mm stainless steel tube and passed through a 135 degree bend a 45 degree bend then a 90 degree bend into the chimney. The flame length was at times ~1 metre long inside the tube.

For your application you want to shorten the flam as much as possible and that requires getting rid of the "Wendelbo secondary air sheet".

I mentioned the " blurting" of the holes before and you could try shaping only some of them so the impetus of the air entering the gas stream was different on adjacent holes. This would create a lot of local turbulence.  The obvious effect will be a shortening of the flame. The pulsing is a distraction. It is due to the relatively low flame speed and the captured volume in the upper part of the chamber.

It is probably possible to get all the gas burned in the gap between the top of the fuel and the exit hole.

For the record, Paul Anderson talked about a "concentrator ring" a long time ago, and he saw that first at my factory in Matsapha. I showed him how the use of a device like that could bring the smoke and random flames together in the centre and burn the smoke. That was a short chimney stove for cooking fueled by coal. There is a similarity between that stove and yours which is the relatively large diameter body and small diameter outlet.

The device I used was not a simple top disk but a cone with a disk as well. It looked like a capital letter A with a flat hat on top. It was removable. After fueling and ignition, the device was dropped in place. The hole was even smaller than your suggested pluse-free minimum but the secondary was not in a sheet form. The result was "pretty good" but not stunning.

Paul used to come to the factory regularly in those days as he was working in Mozambique and we played around with a lot of shapes because of the equipment in the metal shop.

Several stoves came out of that early work: the champion Gasifier, the Vesto, the FSP kerosene stove and later the crossdraft stokes culminating in the KG4 and the BLDD series, with much of that progress happening in Mongolia.

I heard rumours that a downdraft coal stove was being made in Ulaanbaatar in 1906.  It is hard to find something new.

Regards
Crispin
From: winter.julien at gmail.com<mailto:winter.julien at gmail.com>
Sent: June 22, 2020 9:37 PM
To: stoves at lists.bioenergylists.org<mailto:stoves at lists.bioenergylists.org>
Reply to: stoves at lists.bioenergylists.org<mailto:stoves at lists.bioenergylists.org>
Subject: [Stoves] Studies of pressure variations in a TLUD - Pulsing Flame with Concentrator Rings

Hi Crispin;

Thanks for your helpful comments.  It is an interesting problem, and we can see if there are some critical experiments that could refute your hypothesis.  If your hypothesis can't be refuted, then it gains corroborating evidence (after Karl Popper).

I do use holes in the side wall of TLUD reactors, such as in the Akha Stove, to make them more dependable.  (The last thing a cook wants is a flamed-out, smoking TLUD, and that could kill stove acceptance.)  However, this has not been examined systematically, and that is what I am about to do.

Creating cenelations at the top of the TLUD reactor, at the entry point of the secondary air, is not something I have seen before.  That could help the entrainment of reactor gases into moving secondary air.

One might be tempted to create swirl with metal fins at the crenelations.  I don't think that is a good idea.  In the past, I have experimented with giving the secondary a horizontal-tangential component of motion to create a rotating swirl.  Rotation might increase turbulent mixing with forced air, but under natural draft conditions, I have observed a fire 'tornado,' in which, theoretically, there is actually less turbulent mixing than with non rotating secondary air.  As a result, flame height increased as the rotation of ambient secondary air increased.  That is supported by published research where the ambient air around a fire is rotated.

In a couple of weeks, I will post some results, and it will be clearing what I am up to.

Cheers,
Julien.



--
Julien Winter
Cobourg, ON, CANADA
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