[size=18]When designing these stoves, builders should try to bear in mind that rocket stoves are efficient for TWO basic and combined reasons. [/size]
First, there is a highly efficient burn, giving maximum heat from a given fuel quantity.
This is achieved by way of the primary (fire box) , secondary (lower burn tube with re-oxygnation) and tertiary (middle and upper burn tube) burns being almost perfectly reflectively insulated (ideally, with ceramics).
Also, this insulated burn process is appropriately (sic) oxygenated .... and re-oxygenated, allowing the process to 'accelerate' and reach a maximised 'almost plasma' stage. This should involve (NB) an adjustable restricted supply at the firebox to generate as much gas as possible there, and then, again adjustable, preferably pre-heated, re-oxygenation of the second and third stages to maintain the accelerating burn process as temperatures rise and the particulates and gasses are progressively combusted.
Second, these stoves offer maximum heat extraction This is because, uniquely, rocket stoves should, and usually do (very often by accident of design) produce positive exhaust pressure and, therefore, do NOT require a vertical flue. (This positive pressure is created due to the proportions of the 'throat' design , effectively creating a restriction in the fire path feed to the secondary combustion chamber, such that that the oscillating pressures in the final burn process works as positive 'downstream' pump, exactly the same as a WW2 German V1 or doodlebug engine. ) Anyway, that positive pressure is very useful as it allows the use of a very long, low level, horizontal and serpentine exhaust cum heat exchanger design, such that almost all the heat of the (already very efficient combustion) may then be extracted. QED.
'Rocket stoves' that do not incorporate effective throat-to-riser proportions, or really effective insulation of the entire burn, or a serpentine exhaust, are all rather missing the point, many unwittingly no doubt, harking back to Biblical technology. The basic 'rocket burner' design has been used for years in larger tankers, crude oil fed, to very efficiently produce heat (for warming oil tanks etc.) as well as a relatively cool, totally clean and inert exhaust gas for pumping into void and ullage spaces.
