Design/Engineering Prototype Process

Design/Engineering Prototype Process

The Biolite Woodgas Campstove


Prototype Process

Presented at ETHOS 2009

Jonathan Cedar & Alec Drummond

Patent Pending

Woodgas Camp Stove

The creative process from conceptual to third working prototype.

Patent Pending

Jonathan Cedar

Design Engineer / Banjo Player

Alec Drummond

Design Prototyper / Painter

Patent Pending

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.

Patent Pending

Concept: To create a lightweight biomass stove

with a Peltier Junction as a power source

Patent Pending

First proof of Concept

Before any serious commitment was made it was necessary to see if the

concept would actually work.

Patent Pending

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.

Patent Pending

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.

Patent Pending

Pressure test at 1.5 volts

Various blowers charted to determine optimum pressure.

Patent Pending

Volume test at 1.5 volts

Equally important was the volume of air that the blower could produce

within a certain time.

Patent Pending

Optimum blower size determined

Once the optimum blower for volume and pressure was established it

was printed on a FDM machine.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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


Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

Burn Chambers

The deep drawn cylinders were removed from the thermos.

Patent Pending

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

Patent Pending

Patent Pending

Cross Section

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

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.

Patent Pending

Preparing the Aluminum for Pressing

Each aluminum sheet was carefully prepped for the first stage pressing.

Patent Pending

Top Stove Cap Being Cut

Jigs were set on the mill to cut and trim the pressed caps.

Patent Pending

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 1200 – 1400° F. it was very important to

isolate the heat, not only for safety but for combustion efficiency.

Patent Pending

Complete Stove with Kindling

It’s 1:00 am and the first of five stoves is ready for start up.

Patent Pending

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


Patent Pending

Blast Off!

Patent Pending

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.

Patent Pending

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.

Patent Pending

Happily Cooking Away

Stove is now burning merrily along. There is little or no smoke.

Patent Pending

The End… for Now.

This stove will now go out into the field for testing and evaluation.

Patent Pending

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