Dear Kobus It is pretty clear we need a suite of tests for different applications and fuels. The burn-out test which is far more accurate than a WBT (according to Penn Taylor) is an example of an off-the-wall, not-out-of-the-box test method which is really easy to perform.
The SEET Lab in Ulaanbaatar (Stove emissions and efficiency testing lab) is using a protocol that gives real time thermal efficiency during the burn. It is really interesting to see the efficiency not only drop to zero, but to go negative (sometimes 250% negative) late in the burn as the heat from the stove and fuel remaining drives warm air up the chimney and pulls in cold outdoor air to replace it. As yet we do not have what I consider to be a good solution for the changing composition of the fuel during the burn. If you are burning charcoal late in the cooking session, are you using a different heat value per g burned? If not, how large is the error involved? With coal, the loaded fuel is about 12 MJ/kg at the start and 29.5 MJ/kg at the end. That is a very large change. Something I have noticed is that if you correct the heat content per g burned continuously, the power level does not actually drop off as one is given to think by the fuel burn rate. Normally a plot of mass burned show that the rate drops off as the fuel gets consumed. If the fuel mass burned is compensated for changing properties, the power level is nearly flat for some stoves. This is much against most expectations. Here is something to consider: There is a clear distinction between the way data is captured and processed, and the conducting of an experiment to see which lighting technique or refuelling sequence produces less PM. The stove testing 'protocol' we have been discussing for so long (WBT3 and its antecedents) is an experiment that includes a protocol. Fixing the operation method for a stove is NOT part of the recording and analysis. The EPA has long favoured incorporating a fixed operation method in its 'test protocols' for stoves (and vehicles etc). Many sates or countries copy EPA regulations because they don't know what else to do. The problem is that fixing the operating method stifles innovation. If you have only one way to operate a wood stove and only certain sizes of wood as specified in the test, new fuels, fuel preparations and methods of use cannot be homologated (made legal for general use). South Africa and New Zealand have been rather better at avoiding this trap. Europe, not so successful. In North America it has become difficult to think of a stove test without including a strict specification of how the stove should be operated. Surely it is obvious to all by now that how a stove is operated contributes enormously to how it works. We have so many new stoves and fuels. The test protocol must take cognisance of this reality and not stand in the way of innovation. Regards Crispin ++++++++ Crispin, It's taken 6 years for people to crit on it, well better late than never. Just being cynical here:-) . I appreciate your comments and will follow your lead on WBT. I used to assume the charcoal burning phase was the low power phase, i.e. when the flame goes out you enter the glowing ember stage, especially in the core of the briquette. No visible flame results in poor heat transfer hence the low power output and efficiency. Looking forward to proper, universally accepted WBT procedures or should that be looking forward to applying a new universally accepted WBT in the correct manner. -- Kobus Venter _______________________________________________ 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
