[Stoves] iCan w/ Deflectors @ 20 minutes

[Jock Gill]

Crispin,

Thank you for your very informative response.  I have inserted a few comments below.

The key point is that, if you make a iCan TLUD of my design, one with a secondary air slot and three deflectors, and compare it to a TLUD with conventional secondary hair holes and a concentrator ring, you will see that they have quite different performance characteristics.

Regards,

Jock

Jock Gill
Marketing & Communications
Whitfield Biochar, LLC
Burlington, WA
www.whitfieldbiochar.com

Cell: (617) 449-8111

Sent from my iPad

On Feb 25, 2013, at 8:03 PM, Crispin Pemberton-Pigott <crispinpigott at gmail.com> wrote:

> Dear Jonathan
> 
> The video you sent shows a TLUD gasifier with a 'bluff body' in the
> combustion zone. The reason you find it helpful is the same reason the
> 'concentrator disk' is used. It helps maintain the flame when disturbed or
> uneven in any manner. As a flame is self-disturbing they always assist.
> There are many variations on the theme. They all work.

Observation suggests that this only part of the benefit of deflectors.  They also appear to:

1. Increase turbulence, yielding cleaner combustion, as in a TDI diesel;
2. Keep the combustion mainly contained in the combustion zone;
3. Prevent the establishment of stable central spire of flame;
4. Create a very clean combustion with very clear stack gases.

As for persistent central spires of flame, I have observe that such spires often eject considerable streams of soot particles.  I get cleaner results when there is no persistent central flame spire.

> 
> There are other ways to use the function provided by a bluff body. I have
> used a central one with a circular space around it, spraying paraffin at the
> middle of the disk and using the bluff body as a flame retaining impediment
> to gas and air flow. The advantage of such a system is that when the central
> disk is removed (falls off because the stove tips over) the fire
> self-extinguishes immediately.

Interesting.  I achieve the same central disk effect when I put pots inside the flue pipe with sufficient space around the pot for flue games to escape.  Of course the Swiss Volcano Stove uses this same technique and is where I learned to put pots in the flue in the first place.

> 
> I found out today that gas water heaters that have concentric direct intake
> and vent pipes (no fan on the exhaust). When the pipe is less than 30 inches
> long, a bluff body is placed across the vent to create a slight
> back-pressure to stabilise the natural gas flame. It is no more than a
> rectangular strip and two screws.
> 
> If you were to reduce the amount of secondary air I think your can stove
> would have a more stable flame. It runs at a very low power and would
> benefit from a small air supply. This sort of thing is very difficult to
> tune precisely without a combustion analyser because you need to watch the
> CO/CO2 ratio while reducing the air, to the point where the CO/CO2 ratio
> starts to increase. There is no magic number to seek - I find all sorts of
> inflection points. You can, without any instruments, tweak the air closed
> until your eyes water when placed in the gas stream. Eyes are pretty
> sensitive!  It has a lot (or everything) to do with the layout of the parts.

Interesting.  As I find that the pyrolytic process in a TLUD produces variable amounts of syngas over time, especially as the pyrolysis zone nears the primary air source, the gap would, ideally, be automatically varied by sensors and a motor.  Absent that, I find the fixed gap I am using works quite well on average.  A bit to too lean in the early stages, then about right, then too rich, and then back towards lean. Sort of a Goldilocks result.  Hugh has suggested that there is almost never enough secondary air in many TLUD configurations.

I note that the bench model Whitfield continuous feed pyrolytic reactor requires constant variations in the heat supplied to the reactor to maintain a relatively flat line performance at a target rector temperature.  This is all controlled very tightly with sensors very successfully.  The same approach also works well in the industrial scare reactor under development.

 But you are right, there needs to be a lot of experimenting around the gap size, especially as the diameter of the fuel chamber increases.  A fuel chamber with a 6 inch diameter, with its greater pyrolytic surface area, produces a lot more gas per unit of time at a variable rate.  This is evident by the average rate at which it converts biomass to charcoal, which I measure in grams per minute.  The tuna fish cans and Costco Coffee cans I work with are both 6 inches in diameter.  iCan TLUDs made from these cans require a different gap size, but a good average gap can be found with some trial and error work.

Please tell me more about what the eyes tell you.  I have noticed that some configurations I have used make my eyes water.  The current one does not.  Also some stack gases really aggravate the nose and throat.

Cheers,

Jock

> 
> Thanks for sharing
> Crispin
> 
> 
> Subject: iCan w/ Deflectors @ 20 minutes
> 
> Flame action in combustion zone
> 
> 
> 
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