Dear Andrew >Yes Crispin but it makes my case for using a tube to separate the primary and secondary supply more intuitive.
I am with you on that but exploring the more radical idea of tuning the hole to the product to give correct air (maybe 100% EA) with no additional holes. I am not yet convinced that an angled gravity-infeed won't work - the way the VITA stove ran before David Hancock thought of the side feed that became the Rocket Stove. David was at Aprovecho in the old days when that inclined feed was the state of the art. The problem was the fire progressed up the fuel to the air inlet. It seems that with proper air control (which was not well understood in the early 80's) that would not have happened. So back to the past it seems: get the hole size matched to the fuel properties, then incline Rok's feed chamber and give the stove enough height to pull like crazy on the air through the hole. I don't suppose Rok has tried a nearly vertical bottom-lit briquette, has he? Something like a downdraft at maybe 60 degrees up from horizontal? If the briquette was hard enough, it may work really well. The GTZ 7.4 stove in UB was running on wood briquettes (they call them) which means a 50mm hollow log. It was working really we save for the fact they really had the fire burning in the hopper which it was NOT designed for. I am suggesting that the air hole may be suitable for a high velocity air supply. It is probably worth my trying to run it in that mode. Hmmm...... I think I will do that maybe in February. >With a traditional burner all the primary air passes through the bed and if the bed is thick and hot enough no primary oxygen survives into the secondary combustion area. Yes that is traditional but it is becoming a bit passé because there are just too many alternatives showing that with hard fuel (which densified wood logs are but one) it is not difficult to get secondary air past the fuel. With a hollow briquette even light density fuels are going to see this 'exception' being reliable. >I'm simply surmising that if the amount necessary for primary combustion passes around the tube or along side the briquette and the remaining 8kg is induced up the middle of the tube then we can have primary air control for power. I understand. Having tried many times I am backing off recommending central tubes in the combustion area until I see one that will survive the temperatures. Generally, if a central tube is needed, something is wrong and the tube is being inserted to overcome a problem that should not exist. When the power starts to drop, the tube kills the combustion, big time. Cecil Cook loves the idea and I think I was able to spike it with a number of demonstrations. It is an indication of failure, basically. >The secondary air will be proportional to the power and largely self regulated by draught. Yes, but only for a given power level. The domestic stove needs to vary both primary and secondary automatically. If you try some things, try down-drafting the secondary air with preheating like a Vesto to get that to auto-balance across perhaps a 3:1 power range. That is an achievement in itself. >I see Tom has chimed in with similar thoughts. Tom has some ideas worth trying. >As I said before, if the geometry of the fire and hole can be made to do theis then great. My experience of providing all the air via the same jets is it leads to high excess air, yet it does look like modern pellet burners, using a blast tube approach are tending that way. Agreed - they are throwing the secondary past the fuel's primary burn. Simplicity when you can manage it. Imagine how difficult that would be if the secondary air was a fixed supply and the primary and fuel variable. >Well just a couple more: some small 3mm telltale holes could be drilled in the feed tube, they would supply some primary air but also indicate to the cook when the fire was burning back and a new briquette needs screwing in. I like the vision thing. Good point. We are leaving a single hole in the ELCD stove fuel door just for looking to see how things are going. The air is definitely not needed by people complain.... Holiday regards Crispin in the snow _______________________________________________ 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
