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View Full Version : Woodgas Stove - 2nd attempt - now with a fan.



Big_bazza99
16-09-2010, 15:26
After making a "passive" woodgas stove (previously posted) and purchasing a "Woodgas Campstove LE" commercially manuafactured fan assisted woodgas stove, I thought I would try to make something similar.

My stove is made from 2 metal tins purchased from the supermarket, with the smaller can mounted inside the larger and a number of holes made to allow airflow. The fan is attached by a number of bolts and is powered by a 9V battery.

Initial tests were promising, with the outer tin staying cool and the fan really making a difference. Prolonged testing melted the fan!!

Anyone know of a suitable fan that would work for this application, when the plastic fan was on, it really made a huge difference to the burn rate and the heat (which no doubt caused the melting!!).

Video of working stove on YouTube.

http://www.youtube.com/watch?v=UFTbI4A3WcU

Teepee
16-09-2010, 21:29
I've spent more time making fan powered T-luds than is healthy, Its a bit of an obsession of mine.

You really need to put some distance between the inner can and the fan. Both conducted, and radiant heat are the culprits. Radiant heat transfer follows the inverse square law, and giving it a few inches will solve the problem. I glue foil to my fans and this reduces the heat they absorb. It is possible to keep them from being damaged, I have done literally hundreds of burns on one fan, and its still fine.

As far as I know, getting heat resistant fans in the required size, weight and voltage is difficult. Another way of reducing heat damage is to use a small centrifugal blower, they produce more pressure than axial fans, and so will push the air through narrower passages.

To stop fan heat damage when you are burning charcoal, the fan will need much greater distance and a non conductive fan cowling material, say thin titanium or stainless. Ive had results with drinks can metal, but its a bit too flimsy in my opinion to be practical.

I moved my fan to the side in order to stop ash dropping onto the fan, increasing the distance and it also provides much more air flow for the same fan input power. Bringing in air from the sides to an axial fan severely reduces its efficiencey. You could use a high flow 40mm fan and get similar results.

Well done on the stove Baz, good job. Welcome to the tlud club. goodjob.

slammer187
16-09-2010, 21:55
Nice construction but there are a few thing that I have noticed design wise...Your secondary air intakes are very small and your fan is moving more air that the stove can handle, there seems to be a choked air flow so you are decreasing the efficiency of the fan which can be seen by the fluttering flame, by adding more secondary air intakes you will relive some of the pressure and add to the air/gas mix, perfecting this in comparison to the area of the firebox can be difficult but can be improved with the use of a gas wick.

If you adjust your secondary air intakes you will need to adjust your primary intakes...the primary intakes basically control your gas production rate and your secondary intakes control your gas/air mixture...so you will need to increase or decrease your gas production rate depending on the amount of air being mixed with your wood gas...too much air will effectively cool your flame and not enough air will leave unburned carbon.

If you add too many secondary air intakes you could create a flame cap which would reverse your draft and your primary air intakes would become venturies and they would have to adjusted accordingly to the air/gas mixture between the two walls of your stove,
It's all very complicated because there are so many different factors imparted onto achieving a clean burn but keeping these simple things in mind will help you out :)
I recommend one of my videos that I have linked and check out Teepee's videos about his tiny but very powerful TLUD

http://www.youtube.com/watch?v=6A_da97TGTU