[Stoves] gas wick, first try

Jonathan P Gill jg45 at icloud.com
Fri Apr 4 13:41:53 CDT 2014


David,

A few notes inserted below.

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

google.com/+JockGill

Extract CO2 from the atmosphere!

> On Apr 4, 2014, at 12:20 PM, David Young <dyoung at pobox.com> wrote:
> 
>> On Thu, Mar 27, 2014 at 12:16:31PM -0400, Jock Gill wrote:
>> I really hope others will try this FXJ burner design and see what it
>> can do for them.  Have any of you seen a burner like this before?
> 
> Jock,
> 
> You have inspired me to try a gas wick.
> 
> In the FXJ burner, I'm not sure that I understand how the shape and
> materials in the I-shaped member made of washers and copper pipe affect
> the burn, but this is my working theory: the lower washer concentrates
> the wood gas and secondary air into a smaller area and increases the
> speed of their ascent.  The lower washer may also act as a bluff body,
> adding some turbulence: as the gases pass the lower washer, the opening
> up of the combustion chamber will cause eddies to form on top of the
> washer.  The eddies will help to mix the air with the fuel.  The copper
> pipe confines the combustion somewhat.  The top washer concentrates the
> flame & hot air on your pot for better heat transfer.

About right. It looks to me as if makes more sense to force the gases to the secondary air rather than away from it.

As Crispin observes, flamelets allow for better results than flames. Flames suggest sub optimal fuel/air mixing and proportions.

The copper pipe acts a reflector of the secondary air jets. This increases mixing. 

The well defined combustion chamber also increases residence time.  The gases simply can not jump up and out of the stack.  

> 
> Does that make any physical sense?  Is it what you were going for?
> 
> I decided that my old burner deserved another try, so I have put aside
> the burner made of 18-ounce beverage cans.
> 
> I added some more primary air holes to the old burner.  I added a third
> row of 1/8-inch secondary air holes, and I widened the top two rows to
> 3/16 inches.  With these changes, I got more blue flame than before,
> long yellow tips, less red-orange flame licking the top of chimney with
> or without a pot installed.  That is without the gas wick.
> 
> I tried to create some turbulence by putting a fan-shaped insert at the
> bottom of the primary air can, like the Vesto stove does, but I could
> not tell you for certain that that made a difference.  Sometimes the
> flames swirled slightly.  That is also without the gas wick.
> 
> Last night I left out the fan-shaped insert.  I inserted a "gas wick"
> made from a small (10-ounce?) tomato-paste can.  The bottom of the wick
> is at the level of the bottom row of secondary-air holes, and the top
> extends into the chimney by a few inches.  I saw a similar effect as
> Jock did with his new design: short blue flames, short yellow tips, much
> less flame crawling up the chimney.  Some flame did crawl up the wick,
> but only on one side of the burner.
> 
> I was able to start the burner with the wick in place, wood gas
> generation began, but the flame went out after a while.  I was able to
> restart the wood gas after I removed the chimney and the wick.  I let
> the stove burn for a while, and then I gradually lowered the wick into
> the flames and pressed it into place.  Then I reinstalled the chimney.
> 
> I have a couple of guesses about what was going on with the wick last
> night.  First, the wick is too cold at start, and it quenches the
> flames.  

I expect it is because the 'wick' reduces on the draft on the primary air.  The hotter the top of fuel load the stronger the draft draft.

In general, there has to be a strong enough primary air/draft combination  to sustain the startup phase of pyrolysis.  Once established, my systems tend to take 10 to 12 minutes to do this, you are off to the races. 

> I should probably raise the wick.  Second, the burner is very
> sensitive to the wick position: it has to be centered and level or else
> it doesn't shape the flames properly and they will be high on one side.
> I need a better scheme for suspending the wick in the proper alignment.
> 

I suggest you try your wick with top and bottom plates as I do with FXJ burner. Pls let me know your results.

Thanks,

Jock

> I have attached a top view of the blue flame.  Some 1/8-inch steel rod
> steadies the gas wick in the chimney.  It is glowing red hot!
> 
> Dave
> 
> -- 
> David Young
> dyoung at pobox.com    Urbana, IL    (217) 721-9981
> <firstblue.jpg>
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