Wood Gas Cart


After learning detail of 1940 model of wood gas driven truck from Mr. Okazaki, It was decided to make some kind of moving vehicle.

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1940 model of wood gas driven truck

Mr. Tomita who is an owner of greenhouse, Benkei decided to build Wood Gas Cart by converting his gasoline engine driven cart. Now It is a 2m long, 0.8m wide buggy. The engine is 170cc, single cylinder, 4 cycle, 1,800 rpm, 4.5 PS machine.

Mr. Greenwood would design the gasifier using his early version of Design Program for Biomass Gassfication Power Generation.

1. Wood Characteristics

It was assumed to use wood containing 20wt.% of water.

2. Equipment Specifications

Rough estimation shows that this machine can produce 3.53PS as it has 9.18m3/h intake capability at design rotational speed of 1,800 rpm. The diameter of the gasifier will be 200mm and 80cm high.

Downdraught or co-current gasified with single throat central air-inlet from top type was selected as it was also used in Japan in the last World War II.

Gassifier used in Denmark in war time (photo by Mr. Cooper)

2.1 Trial Design

As only operation guide was available, throat velocity of 0.4m/sec was selected as design criteria for avoiding pressure drop. But it does not produce gas for long time.

2.2 FAO Design

For the purpose of avoiding trial and error testing for finding proper geometry of the throat, it was decided to follow design criteria of FAO guide book. It uses Hearth Load as the basis of throat diameter. Wood Consumption base Hearth Load of 0.11kg/cm2/h or Gas Generation base Hearth Load of 0.25Nm3/cm2/h is recommended as maximum figures. It also recommend minimum height of 20 cm for reduction Zone below throat.

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FAO Throat Design and Flow Diagram

3. Detail Mechanical Design and Fabrication

Mr. Tomita was responsible for the Detail Design and Fabrication.

For avoiding toxic gas leakage, induced blower was added at engine air intake as startup blower. Cyclone ash separator was added and final separator will be oil filter. About 1 liter condense accumulator shall be provided just before engine to accumulate condensate for 1 batch operation.

Dual fuel system will be provided for startup and emergency purposes.

Reactor section will be completely covered with internal insulation.

4. Expected Performance of FAO Design

From the experience of trial operation, stable minimum operating range is set by throat velocity of 0.4m/sec. Therefore Engine load of 40% seems lower limit.

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Performance of the cart

5. Completed Cart

The cart was completed in July 20, 2003 and modified in July 29, 2003. Modification was an addition of induced draft blower at the top of vent pipe.

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Completed Cart and Wooden Chips for Fuel

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Induced Blower

6. Test Operation of Trial Design

It was revealed that the engine can operate only in limited time. The cause and remedial actions are as follows:

(1) Actual composition of wood and water content is different from the one used for design calculation. Therefore, gassification air is needed to give more heat. In this case, nozzle are necessary for  limiting excess air flow to avioid gas dilution and to give high velocity head. (not yet)

(2) Heat loss was more than calculated value.----Apply rock wool inside and outside reactor and to wood container. Then, recover heat for preheasting air and wood.(not yet)

(3) Due to low speed in throat air and gas does not flow evenly. Remedial action is to make throat smaller and increase speed. it is also required to extend reduction zone up to 20cm.(not yet)

(4) Condensate accumulate in carburetor.----Modify piping to avoid condensate accumulation in carburetor.(done)

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Starting up by sending air from handheld blower

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generated gas is burned at the top of  vent pipe

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ashes remaining in the reactor after 2 hours operation

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condensate (ph=4)

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slug formed at high temperature

8. Acknowledgement

In February 2004, Mr. Greenwood found a site about wood gassification car made by Mr. & Mrs Pope. Cone internal looks quite similar to Japanese design because this gentleman also copied German Nazi design. http://members.tripod.com/~highforest/woodgas/woodfired.html

Mr. Hans Hochwald who prepared above page also cited various wood gassification technology. Among them following FAO guideline is the best for design guide.

May 6, 2003

Rev. May 31, 2005

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