[Stoves] Studies of pressure variations in a TLUD

[Crispin Pemberton-Pigott]

Dear Julien

Attached is a video of a wood stove with a smoke-filled chamber (from gasifying wood) with a fire at the far end igniting at least some of the smoke, with air supplied from the fueling door.  This is a primitive version of the acetylene cannon.

In the case shown it can probably be resolved with additional draft.

Regards
Crispin

From: Crispin Pemberton-Pigott
Sent: Monday, June 15, 2020 14:43
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Subject: RE: [Stoves] Studies of pressure variations in a TLUD

Dear Julien

Are you familiar with this type of device:

https://www.youtube.com/watch?v=bTa_GicWBuM

It is a machine gun simulator, in that case operating on propane and oxygen.  They used to be made with acetylene which I expect makes a louder noise.  It is used on model aircraft and vintage aircraft to mimic the sound of a machine gun.

The principle of operation is I think what you have accidentally replicated in the stove.  You are producing a combustible gas with at least some oxygen in it, and you maintain above a cavity a flame that is able to light that mixture.  I suspect you have a very low but non-zero oxygen content in the gas below the flame.

The principle of operation of the gun simulator is to fill a pipe with a combustible mixture (say, 15% acetylene and 85% oxygen) from the “back” and to have a spark plug connected to a Model T spark box (which sparks continuously) at the open end of the pipe.  As the gas reaches the spark, it ignites and burns back into the tube, at a very high speed in this example. The gas exhausts explosively out of the tube leaving it full of incombustible gases, which are then displaced from the back by a new batch of mixture. The flow rate and the pipe diameter determine the firing frequency.

Translated into a gasifier stove, it would appear as a pulsation.  You can overcome it by introducing air through at least one hole into the gas near the source (assumed to be the top of the char bed) so that after one pulse, it remains alight.

People have used pulsed gasifier combustion deliberately:
https://www.sciencedirect.com/science/article/pii/S0956053X03000382

I think on a small unit you will not want to because of the enhanced probability of a flame-out.

Regards
Crispin


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