Dear Julien It sounds like you could afford to reduce the primary air supply. If you have things right you should be able to turn it off completely. If you are able to generate a condition that is primary-air-starved, you can then regulate it.
It is not exactly true that a TLUD (or a gasifier or semi-gasifier) has to burn from the top down only. As long as the control over the primary air is complete you can create a good burn. In order to create a decent gas you have to have 'smoke production' so some air has to get into the fuel unless you have a self-heating retort like a WorldStove product. They run on oxygen in the fuel only, basically. Pack in the fuel if you can. Regards Crispin -----Original Message----- From: Julien Winter <[email protected]> Sender: "Stoves" <[email protected]> Date: Thu, 4 Apr 2013 11:37:44 To: <[email protected]> Reply-To: Discussion of biomass cooking stoves <[email protected]> Cc: David Yarrow<[email protected]> Subject: Re: [Stoves] The Art of Using Grass Bundles in TLUD Stoves Dear Paal and Crispin; and Stovers; Thanks for your suggestions on how to use bundles grasses as cookstove fuel. I gave it a go in my natural draft, 3.87-L paint can TLUD with a 15 cm tall, 8 cm Ø chimney fitted to the paint can lid. Secondary air entered through a 4 mm gap under the lid. Primary air entered through twenty-five 4 mm Ø holes in the bottom of the can. I used well-dried wheat straw, and started the fire with a dab of barbeque lighter. Ambient air was 4°C, and a dog was used as a windbreak. Bundling the straw was a definite improvement over filling the can with loose straw, but not an unqualified success. Lightly-packed, loose straw produced a smoky shouldering fire. There were preferential flow paths of the primary air through the fuel, so soon after the TLUD was lit, the ignition fire followed the best path to the bottom of the can. The bottom fire then consumed all the oxygen, and resulted in shouldering in the unconsumed fuel above which produced unburned smoke. Loose bundles of straw that occupied about 75% of the cross-sectional area of the TLUD produced a hot, steady gas fire, but with some unburned smoke (see below). The ignition fire also bypassed fuel, but there remained a clear path for primary air to reach flaming pyrolysis higher up in the fuel. The gas fire stayed alight, but there was periodic unburned smoke, symptomatic of patchy shouldering. The straw was burnt out after about 5 minutes. Tightly bundled straw, and bundles that fully occupied the TLUD, shouldered. As noted above, I didn't get a completely smokeless fire with a loose bundle of straw. I think this relates to my wheat straw coming higgledy piggledy from a bale. With grasses it could be important to primary air flow that the bundles have stems at the bottom and leaves at the top. Also, grass species vary considerably in size and leaf/stem ratio. Tropical grasses with coarse stems likely present a denser fuel that is better aerated, hotter burning and longer-lasting than low bulk density, cool-season grasses. Now with some experience under my belt, I will wait for a good rain to wash the sand and salt off the roads, a warm spring day, and get on my motorcycle to see if can find Alex English. Cheers, Julien -- Julien Winter Cobourg, ON, CANADA _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://stoves.bioenergylists.org/ _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://stoves.bioenergylists.org/
