The Biolite Woodgas Campstove
Presented at ETHOS 2009
Jonathan Cedar & Alec Drummond
Woodgas Camp Stove
The creative process from conceptual to third working prototype.
Design Engineer / Banjo Player
Design Prototyper / Painter
Combining Peltier technology first seen on the Stove Fan with the forced
air efficiency of the battery powered Sierra Zip Stove was the initial idea
behind the Camp Stove. Tom Reed and Paul Anderson’s research on
wood gas technology also proved invaluable to the concept.
Concept: To create a lightweight biomass stove
with a Peltier Junction as a power source
First proof of Concept
Before any serious commitment was made it was necessary to see if the
concept would actually work.
Research and Presentation to Smart Design
Once there was a proof of concept established we began to see if there
was a actual need for such a design. What we found was there was a
potential market for domestic camping and more importantly the
technology could be useful for developing nations.
Start of empirical testing of blower housing and
A centrifugal blower was chosen over a fan because it can generate
greater pressures and has fewer design limitations. These various
configurations were done to determine the optimum size of impellor and
housing for pressure and volume.
Pressure test at 1.5 volts
Various blowers charted to determine optimum pressure.
Volume test at 1.5 volts
Equally important was the volume of air that the blower could produce
within a certain time.
Optimum blower size determined
Once the optimum blower for volume and pressure was established it
was printed on a FDM machine.
Second phase Woodgas test stove
This stove was built to have a fixed 1.5 volt power source and
interchangeable burn chamber to determine the optimum primary and
secondary hole size and placement. A gas/air mixer was also built.
Stove without outer insulating sleeve in place
The sheet metal parts were rolled and bent to fit the top and bottom
caps that were pressed on a simple 20 ton shop press.
Stove with outer sleeve in place and perlite for
insulation before burn chamber and top cap are
Many types of insulation were researched and considered but perlite was
initially chosen because of it’s lightness and low cost.
Complete test stove with adjustable gas/air mixer
This stove was designed to test the optimum gas/air mixture with an
interchangeable burn chamber and adjustable gas/air mixer using a fixed
1.5v power source.
First firing with the gas/air mixer
With the burn chamber removable to adjust the primary and secondary
air jets, the adjustable gas/air mixer and a constant blower speed we
could begin to tune the stove for the best combustion.
Gas/air mixer in place for efficient combustion
Although the gas/air mixer seemed promising it was decided that it was
impractical and possibly dangerous to remove it for refueling while the
stove was in use.
Swirl of combusted gases
With the air flow of the secondary air jets biased in a “clockwise”
direction it was observed that there was improved gas/air mixing within
the burn chamber without the mixer. The longer the gas/air combustion
process was within the burn chamber the more efficient and cleaner the
Testing the Peltier Junction and Heat Conductor
Various TEG’s were tested to determine which required the least heat
differential to generate 0.2 volts to power the motor.
Heat Conductor Tests
Due to space limitations of the heat conducting probe when the power
plant was being stored in the burn chamber prototypes were made for a
removable heat pipe. Tests proved there was too much heat loss
between heat conductor and TEG. A solid connection between the probe
and TEG was significantly more efficient.
Heat Conducting Probe Solution
The heat conducting probe is inserted through the outer housing at a 50
degree angle to lock the power plant and to allow the power plant to fit
into the burn chamber.
Materials for the Third Prototype
One of the most difficult parts of the third prototype was finding a deep
drawn cylinder of the proper dimensions. This was the only part that we
could not produce in house. The burn chamber came from a thermos
liner from NYC’s Chinatown.
The deep drawn cylinders were removed from the thermos.
Third Prototype CAD
With all the data and a fixed size for the burn chamber the drawings
were then completed. The main stove parts were:
R- stove Body E- power Plant O- stand-off D- heat shield P&Q- legs
SLS Parts for Power Plant
Glass filled SLS parts were chosen over high temperature resin castings
because of time and price constraints. These parts were designed to
withstand 350° F.
Laser Cut Heat Shield
After heat conductivity and insulation tests a simple 24 ga. stainless steel
heat shield was designed to surround the stove body to improve the
Laser Cut Pot Standoff
The first mock-ups were cut from paper. Once the design was confirmed
it was redrawn in CAD for export to the laser cutter.
Tool for Top and Bottom Stove Caps
This was a three stage tool to press the caps from annealed 1100
aluminum using the shops 20 ton hydraulic press.
Preparing the Aluminum for Pressing
Each aluminum sheet was carefully prepped for the first stage pressing.
Top Stove Cap Being Cut
Jigs were set on the mill to cut and trim the pressed caps.
Light weight refractory insulation was used after numerous tests were
done with other high temperature insulations. With the burn chamber
reaching temperatures of 1200 – 1400° F. it was very important to
isolate the heat, not only for safety but for combustion efficiency.
Complete Stove with Kindling
It’s 1:00 am and the first of five stoves is ready for start up.
Stove at Initial Stage of Start up
Notice the wood gases igniting at the secondary air jets as the TEG
produces power the blower begins to force air into the combustion
Clean Efficient Combustion
TEG is generating power to the blower which is forcing air into the
primary and secondary air jets to create very efficient combustion.
First Pot on Stove
The sheet metal stand-off was designed not only to keep the pot a
proper distance but also to keep the flame within the pots outer
boundaries. This increased combustion and heating efficiency.
Happily Cooking Away
Stove is now burning merrily along. There is little or no smoke.
The End… for Now.
This stove will now go out into the field for testing and evaluation.