[Stoves] Riser Height and a 'Counter-Current' Woodgas Burner - YouTube Vid

[Jock Gill]

Julian,

Interesting video. 

1. I would try this with a flame retention disc rather than a central hole.  I view central holes above fuel bed as a fundamental error.  I know central holes are the given wisdom, but I view them as the source of problems that can not be overcome.  They are a barrier to better achievements.

2. I would strive for the maximum amount of blue flame. I did not see any in your video.  People want to cook with blue flames. Aspirational.

3. Perhaps an hour glass type device might work?  Could be asymmetrical?

Cheers,

Jock

Jock Gill
P. O. Box 3
Peacham, VT 05862

google.com/+JockGill

Extract CO2 from the atmosphere!

> On Jan 25, 2016, at 7:10 PM, Julien Winter <winter.julien at gmail.com> wrote:
> 
> Hi all;
> 
> 
> 
> I have posted a video on YouTube on Riser Height and a 'Counter-Current' burner that continues on the theme of discussions earlier this month about premixed flames.
> 
>  
> 
> https://youtu.be/KzYUzJPM3eQ
> 
>  
> 
> The purpose of this video is to demonstrate the importance of riser height on the function of a natural draft, top-lit updraft gasifier using the “Counter-Current Woodgas Burner” (CCWB).  Riser height affects the flow rate of both primary and secondary air, and the degree of turbulent mixing of woodgas with secondary air.  Increasing riser height creates greater buoyancy forces that can improve the efficiency of stove combustion, and stove responsiveness for the operator, but it can lead to excessive secondary air, and excessive turbulence under some conditions.
> 
>  
> 
> With a true counter-current burner, the fuel gas and oxidizer gas collide head-on.  This is more-or-less what happens with the CCWB, because a downward laminar flow of secondary air is sent against the upward flow of woodgas.  However, it is not a perfect counter-current burner, because a lot of the secondary air is pulled sideways by the buoyancy force created in the gas flame.
> 
>  
> 
> The main objective of the CCWB is to get a much turbulent mixing of secondary air and woodgas at the base of the gas flame as possible.  We are trying to approach an ideal of a pre-mixed flame at somewhat above (to be determined) the stoichiometric requirement for oxygen.
> 
>  
> 
> The second objective of the CCWB is to locate the base of the flame over the fuel bed char.  Some secondary air supports glowing char, and sustains a higher temperature in the fuel bed, from the ignition front up to the top of the char, than would be obtained if the secondary air and the gas flame were located at some distance above the fuel bed.   Glowing char can help with cracking of tars, and provide heat to assist in the piloting of gas ignition.  This helps maintain woodgas flame stability at low gasification rates.
> 
>  
> 
> Some modifications of the CCWB have been tried, but did not show much benefit.  (1) A ring of small air holes (of various numbers and diameters) in the sidewall of the reactor were positioned just below the inner riser.  It was thought that these holes would provide small flamelets that would keep the gas flame from extinguishing at very low gasification rates.  It was found that these holes didn’t help, and functioned more to diminish the role of the counter-current air flow. (2)  Various fins were made at the bottom of the internal riser to see if they would increase turbulence.  Fins were found to be unnecessary.
> 
>  
> 
> The stoves in this video are prototypes.  They are working hypotheses that need scientific stove testing to optimize their geometry, and validate the counter-current approach. To become working stoves, they need a regulator for primary air, an insulated external riser, and mechanism to transfer the heat to the pot or other object of work.
> 
> 
> 
> If the CCWB can be shown to improve combustion efficiency on diverse biomass fuels, and over a wide range of gasification rates, that would be good, because it is a very easy burner to build.
> 
> 
> 
> Cheers,
> 
> Julien.
> 
> 
> 
> -- 
> Julien Winter
> Cobourg, ON, CANADA
> _______________________________________________
> Stoves mailing list
> 
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
> 
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
> 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20160125/026b327e/attachment.html>