The Biolite Woodgas Campstove

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Marcia Singleton
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1 The Biolite Woodgas Campstove Design/Engineering Prototype Process Presented at ETHOS 2009 Jonathan Cedar & Alec Drummond

2 Woodgas Camp Stove The creative process from conceptual to third working prototype.

3 Jonathan Cedar Design Engineer / Banjo Player Alec Drummond Design Prototyper / Painter

Stove was the initial idea behind the Camp Stove.

4 The Inspiration 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.

5 Concept: To create a lightweight biomass stove with a Peltier Junction as a power source

6 First proof of Concept Before any serious commitment was made it was necessary to see if the concept would actually work.

7 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 impellors A centrifugal blower was chosen over a fan because it can generate greater pressures and

8 Start of empirical testing of blower housing and impellors 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.

9 Pressure test at 1.5 volts Various blowers charted to determine optimum pressure.

10 Volume test at 1.5 volts Equally important was the volume of air that the blower could produce within a certain time.

11 Optimum blower size determined Once the optimum blower for volume and pressure was established it was printed on a FDM machine.

12 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.

13 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.

14 Stove with outer sleeve in place and perlite for insulation before burn chamber and top cap are installed Many types of insulation were researched and considered but perlite was initially chosen because of it s lightness and low cost.

15 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.

16 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.

17 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

18 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 combustion.

19 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

stored in the burn chamber prototypes were made for a

Tests proved there was too much heat loss between heat

20 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.

21 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.

22 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.

23 Burn Chambers The deep drawn cylinders were removed from the thermos.

24 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

25 Cross Section

26 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.

27 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 stoves safety.

28 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.

29 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.

30 Preparing the Aluminum for Pressing Each aluminum sheet was carefully prepped for the first stage pressing.

31 Top Stove Cap Being Cut Jigs were set on the mill to cut and trim the pressed caps.

$Insulated Chambers Light weight refractory insulation was used after numerous tests were done with other high temperature insulations.$

32 Insulated Chambers Light weight refractory insulation was used after numerous tests were done with other high temperature insulations. With the burn chamber reaching temperatures of F. it was very important to isolate the heat, not only for safety but for combustion efficiency.

33 Complete Stove with Kindling It s 1:00 am and the first of five stoves is ready for start up.

34 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 chamber.

35 Blast Off!

36 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.

37 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.

38 Happily Cooking Away Stove is now burning merrily along. There is little or no smoke.

39 The End for Now. This stove will now go out into the field for testing and evaluation.

Some Experiments With Sawdust-Burning Stoves

Some Experiments With Sawdust-Burning Stoves Report To ETHOS 2008 by Jim Wilmes Background For the past two years I have been working as a volunteer in Lima, Peru, teaching people to build rocket stoves