Dear Richard and Andrew I know we all quote the 6 kg of air for burning biomass please keep in mind that to get an excess air ratio of about 100% it takes twice as much as 'it seems'.
With the gasifiers, the ratio between primary and secondary might be a 1:6 split, but the secondary needs to provide all the excess air as well so it is more like 1:10 than 1:6, yes? The primary side for the gasifiers needs to remain the same (which is based on experience, really) but the theoretical need for air on the secondary side is surely less than the real need? So when it comes to the air moving through the hollow briquette, can we treat the whole needed air supply as being present 100% (instead of a separate secondary supply) and concentrate only on mixing and combustion chamber temperature? It looks as if the hole is a means to sneak the whole air supply past the light biomass fuel without increasing the burn rate which is what happens in most ordinary fires. I think Paul made this point clear when we were talking about getting secondary air through the coal bed earlier in '10. So, one big advantage of using hollow briquettes is that it is probably possible to get the whole air supply through in one go and avoid having the complexity of secondary admission. This being the case, it should be possible to create a perfect hole size for each briquette mix and compression/forming method. This means in practice that for any consistent product, one should vary the hole diameter and test them in a stove, measuring the excess air. A simple method to do that is to look for visible smoke most of the time. That means the air supply is inadequate. On the briquette press side, it means having replaceable cores with many diameters. Fully implemented, one could select briquettes with the appropriate burn rate: denser probably needing smaller cores to have the right air supply to burn slower and longer. Got thoughts on this? Regards Crispin NOT in the snowstorm _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address Stoves mailing list 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/ [email protected] http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
