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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Dear Paul<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Well, you are going to have a classification problem with a TLUD (which is a flow direction) if it doesn’t have a migrating pyrolysis front. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>So, please do not confuse the TLUD (which is MPF) with something that is lit at the top maintains its burning at the top. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Huh? If the fire burns ‘openly’ meaning large particles and has air flowing through and does not have a ‘coking stage’ following by a coke burning stage, what is it? It is a normal fire that is top lit that slowly burns down – but there are flames and smoke and CO and PM being produced throughout the fuel bed. The fire works its way to the bottom. It is not ‘pyrolysing’ in any sense similar to a TLUD pyrolyser creating a combustible gas that is burned above the fuel bed. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal>This research paper is clearly NOT referring to what has become known as the TLUD micro-gasifier. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Well they are certainly TLUD’s but they are definitely not micro-gasifiers. The reason they burn about 80% cleaner (multiple tests) is because they have a coke bed on top of the fuel pile. But here are flames throughout the fuel, eventually. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>A fire of that type can be created by making the particles and air gaps larger. You could use as a metric the combustion chamber diameter (or area) and the fuel particle diameter (or area). If the ratio is 6:1, it can work as a TLUD or BLDD and be pretty clean. If the ratio is smaller, it won’t work properly. At 10-15 times it is going to be a pyrolyser if the air flow is controlled.<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>Yes, people can light fires at the top. They can be just regular fires. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>When I was a Boy Scout they taught us to light really big fires on top. That was to reduce smoke. Is that a regular fire? A BLUD fire makes a heck of a lot more smoke and we didn’t do that.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>That is why I am emphasizing MPF as being the important characteristic of TLUD stoves. Others that are LIT on the top or bottom are not necessarily gasifiers. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Agreed, and I would not classify the mbaula as a gasifier in the sense you use. You are drawing a thick line between types and there needs to be some finer lines in there. A TLUD ordinary fire burns cleaner than a BLUD with the same fuel. A TLUD in a closed space with good primary air control can be a gasifier or a pyrolyser, the latter having a narrower definition, I think, about its hot zone. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Because all coal and wood fires are ‘gas fires’ where do you place a fire that is burning a particle of fuel for two hours? The fire works its way down the pile, long before it finishes pyrolysing or burning the upper portion to ash. </span><br><br><span style='color:#1F497D'>></span>The designations of UP and DD for updraft and downdraft are term for GASIFIERS (PHYSICAL DEVICES) WHERE THERE IS AN INTENTIONAL AND CLEAR SEPARATION OF WHERE AND WHEN THE GASES ARE CREATED AND WHERE AND WHEN THE GASES ARE BEING BURNED. <br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I don’t think so. Where is that from? Updraft is a direction of draft. Up, cross, down. The Franklin stove is both down and cross drafting, i.e. on an angle.<o:p></o:p></span></p><p class=MsoNormal><br>A TLUD is a gasifier. Lighting coal or wood in a bucket is not a gasifier. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Well, not quite – a TLUD could be a gasifier or a fire. Some TLUD’s are gasifiers. Some are pyrolysers. Some are neither. The critical difference for the last case is that the fuel particles have to have access to adequate air to burn completely but do not do so in a short period of time.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>All fires involve gasification (a process), but that does not make the device (bucket, open air, tube, whatever) automatically to be a gasifier DEVICE. <br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Agreed. If it is making combustible gases which are aflame from the fuel particle, through the whole fuel bed and above it towards the pot, that is not a gasifier. But it is still without question a TLUD device and we encourage people to light it like that.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>There is a down-side to this BMG mbaula: If it is lit on top, it gives of significant PM throughout most of the burn – certainly far longer than if it is bottom lit. The total PM emitted is much reduced, but it is not a clean fire to cook on. That is mostly to do with the device, not the fuel. Fuel size is a factor, but the cause is the device. For the cook, they may prefer to have the coal coked in the beginning as rapidly as possible, then cook on the coke, indoors on occasion. This is definitely the preference for space heating using the same device.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I am pointing out that running the mbaula as a TLUD means having significant PM emissions for a much longer time which may affect the cook and the taste of food more than the BLUD method which gets rid of the volatiles in one horrendous go.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>In order to burn the coal ‘cleanly’ meaning without small or soot, one has to use a proper stove tuned to that fuel. I can’t see that happening without a chimney which is needed to get the proper velocities and pressures.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p></div></body></html>