Hi I am interested in the Protos stove. Its principle of operation is that pressureised plant oil enters a stainless steel tube where it is boiled/vapourised, then exits as gas through several nozzles into a combustion zone.
I have built a larger scale stove which uses a similar principle: Oil is fed into the bottom of a 340g welding gas bottle through a steel tube. The welding gas bottle is a 3" diameter 12" high steel cylinder with hemispherical ends. There is another steel tube welded into the bottle such that the open end inside is situated near the top of the bottle The other end of this tube protrudes about an inch beneath the lower hemisphere of the bottle, is welded closed and has a small (2-3mm) hole for exit of gas. This is the gas outlet tube. I will refer to this overall assembly as the 'evap chamber'. The evap chamber is situated centrally inside a chimney made from the cylindrical portion of a CO2 bottle (i.e. I cut the ends off). This is a 40" long, 6" diameter, 1/4" thick steel cylinder. To the base, there are four 2" wide x 4" high fins opened outwards to admit and swirl combustion air. The location of the evap chamber within the chimney is such that the gas exit is toward the bottom of the combustion air intake. I will refer to this overall assembly as the combustor. The combustor is situated within a 12kg butane cylinder. This is an 18" diameter, 24" high cylinder with hemisperical ends. The butane cylinder has an opening at the top which both radially locates the combustor and admits combustion air around the periphery of the combustor. The combustor is inserted through this opening and rests on the bottom of the butane cylinder. The oil feed pipe from the bottom of the evap chamber exits the centre of the lower hemisphere of the butane bottle through a small airtight hole. A 24" chimney is added to the top of the combustor to increase draught. The principle of operation is thus: The oil enters the evap chamber and is gasified. The oil will either evapourate instantly, or there will be some liquid in the chamber. As long as the liquid level is below the top of the gas outlet tube, gas will exit through the small hole in the bottom of the tube at a pressure determined by the oil feed pressure. The motivation for the butane cylinder is to pre-heat the combustion air. Cool air is drawn in around the top of the cylinder, flows past and is preheated by the combustor and finally enters the combustor towards the base. Following combustion, the gasses in the chimney are much hotter and lighter, therefore rise up th chimney and drive the intake of further combustion air in a continuous process. The combustor's finned air intake, combined with the constriction caused by placement of the evap chamber within the combustor, causes intense swirling of the flame in the volume between the evap chamber and the combustor's internal wall. Experimentation shows that operation is most effective if the gas jet is directed through one of the finned openings so that the flame shoots out into the butane bottle, swirls round, then is drawn back into the combustor. My question: The stove I have described is passive and burns very cleanly; There are no visible emissions when it is up to temperature. However, I have observed that the evap chamber becomes clogged with carbon deposits due, i expect, to pyrolysis. Pyrolysis occurs when oil is brought into contact with a hot surface and some of it turns to solid carbon. Does anybody know how the Protos stove deals with this problem? Is it engineered so that no significant carbonisation occurs, or is regular unclogging required? Regards Jonathan
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