Dear Paul and All Having made a stove I called a semi-gasifier for years I will chip in that the term is my view means that it can operate in more than one mode.
The description you gave of staged combustion takes place nearly all the time so I am a little more cautious about strictly dividing the stoves into groups. All fires are gas fires (save a tiny part of solid fuel combustion). It is easy to demonstrate that some fires have primary combustion then to more distinct stages with secondary and tertiary air. Stove architecture may emphasize this or not. A semi-gasifier can burn as a TLUD to start then continue as either a refuelled BLUD or a pyrolyser without any particular direction to the front, just that it continues in a controlled air environment. The 'direction' concept is correct for some fires and not others. If the mode can be selected by moving a lever then the user has some or perhaps a lot of control over then firepower which is, after all, the purpose of the complexity. As the fuel condition may vary, the user needs to add the appropriate amount of air to the fire to get the desired heat level. Consider: a hot TLUD that has almost completed its char burn is refuelled. The primary air is almost completely closed. The fuel will pyrolyse and combustion may not continue from the bottom only - it may return to a gas-producing mode that does not have a vertical component but rather an inward component towards the centre of the fuel particles. This can easily be demonstrated by refuelling with different diameters of fuel. The thin fuel will pyrolyse easily and rapidly. Thick fuel will not, yielding a long low flame. In both cases the 'fire' is neither at the bottom nor the top. It is a self-heating retort, basically. Downdraft fires which are allowed to create a coke/char burning bed can easily return a pyrolysis front style combustion by adding fuel on top of the char. They are extremely PM-clean when being refuelled as the hot bed is already established. With a top-loader the transition may not be as smooth. So far I have not seen a stove which can be turned from a char burning state back into a TLUD save one which is the Mongolian Rotating Grate (from Inner Mongolia). I made a video of it with Profs Lodoysamba and Tseyen-Oidov and posted it on this site. It is also on YouTube if I recall correctly. It can be refuelled and flipped with a crank to return to a TLUD fire. It is poorly executed but the concept is articulated by the designer and definitely works. As it really has only one combustion type I never considered it a semi-gasifier as it does not have enough air control to pyrolyse fuel properly. Perhaps these descriptions will inspire new and clearer nomenclature. What I would like to see is room for new ideas so people learning about stoves are not channelled into mental ruts about how things have to be. Regards to all from sweltering Battambang, Cambodia Crispin -----Original Message----- From: Paul Anderson <[email protected]> Sender: "Stoves" <[email protected]> Date: Tue, 30 Oct 2012 14:05:53 To: Discussion of biomass cooking stoves<[email protected]>; [email protected]<[email protected]> Reply-To: Discussion of biomass cooking stoves <[email protected]> Subject: [Stoves] Gasifier stove grant (and semi-gasifiers) _______________________________________________ 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://www.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://www.bioenergylists.org/
