Evaluating Common YouTube Rocket Stove Designs
Jan 31, 2019 17:41:45 GMT -8
pinhead, Piet, and 5 more like this
Post by DCish on Jan 31, 2019 17:41:45 GMT -8
Many YouTube "Rocket Stoves" appear similar to designs being developed here. However, these builds often do not reflect an awareness of several key principles of combustion that lead to the truly high levels of efficiency being pursued on this site. There are three primary variables central to getting clean, high-efficiency combustion:
- Temperature -- the higher the better until you pass 2200F or so where you can start to form other nasty byproducts (That's not something we have to worry about with natural draft wood burning appliances, though, which routinely max out in the 2000*F (1100*C) range when optimized for high temperature combustion)
- Turbulence -- the fuel molecules have to be able to interact with the oxygen molecules, so good turbulence is essential to mix things together and approach complete combustion. Of course, creating turbulence also creates friction, something you want to minimize, so you're always chasing the best balance possible.
- Time -- Combustion of wood fuel takes a while, so you have to create an environment that will sustain high temperatures and turbulence over enough time for all the fuel particles to burn
All of this background to say this about the operation of a "standard J-tube": The short initial downward part of the "J" provides the ideal angle for fuel to be pulled in by gravity with as little hang-up as possible. Combustion happens at the bottom of the J until it hits the 90* upward turn into the long part of the J. This abrupt transition induces strong turbulence. The upward part of the J is also insulated, providing additional time for mixed air / combustion gases to finish burning.
What is missing from a lot of the "V" tubes you will see on YouTube:
- Temperature -- Most of the V tubes I see on YouTube are fabricated out of bare metal with little to no insulation. A well-build J tube will achieve high enough temperatures to rapidly degrade the metal that these are made of, so, paradoxically, if they were burning well, they would self-destruct.
- Turbulence -- the fuel entering at the bottom of the upward tube leads to a simple, straight combustion path with minimal to no turbulence induced
- Time -- Although a V tube may have a sufficiently long riser, with no insulation and poor mixing, combustion temps fall and the combustible gases stop burning before all the fuel is consumed
Some fun reading about how much of the stuff here developed:
General "getting started" stuff:
donkey32.proboards.com/thread/1/welcome-start
J Tube:
donkey32.proboards.com/thread/355/small-scale-development
Batch box:
donkey32.proboards.com/thread/511/adventures-horizontal-feed
Happy reading!!!
- Temperature -- the higher the better until you pass 2200F or so where you can start to form other nasty byproducts (That's not something we have to worry about with natural draft wood burning appliances, though, which routinely max out in the 2000*F (1100*C) range when optimized for high temperature combustion)
- Turbulence -- the fuel molecules have to be able to interact with the oxygen molecules, so good turbulence is essential to mix things together and approach complete combustion. Of course, creating turbulence also creates friction, something you want to minimize, so you're always chasing the best balance possible.
- Time -- Combustion of wood fuel takes a while, so you have to create an environment that will sustain high temperatures and turbulence over enough time for all the fuel particles to burn
All of this background to say this about the operation of a "standard J-tube": The short initial downward part of the "J" provides the ideal angle for fuel to be pulled in by gravity with as little hang-up as possible. Combustion happens at the bottom of the J until it hits the 90* upward turn into the long part of the J. This abrupt transition induces strong turbulence. The upward part of the J is also insulated, providing additional time for mixed air / combustion gases to finish burning.
What is missing from a lot of the "V" tubes you will see on YouTube:
- Temperature -- Most of the V tubes I see on YouTube are fabricated out of bare metal with little to no insulation. A well-build J tube will achieve high enough temperatures to rapidly degrade the metal that these are made of, so, paradoxically, if they were burning well, they would self-destruct.
- Turbulence -- the fuel entering at the bottom of the upward tube leads to a simple, straight combustion path with minimal to no turbulence induced
- Time -- Although a V tube may have a sufficiently long riser, with no insulation and poor mixing, combustion temps fall and the combustible gases stop burning before all the fuel is consumed
Some fun reading about how much of the stuff here developed:
General "getting started" stuff:
donkey32.proboards.com/thread/1/welcome-start
J Tube:
donkey32.proboards.com/thread/355/small-scale-development
Batch box:
donkey32.proboards.com/thread/511/adventures-horizontal-feed
Happy reading!!!
