[Stoves] High temperature combustion in a ND TLUD

Jock Gill jg45 at icloud.com
Tue Apr 8 08:36:38 CDT 2014


Crispin,

I too am a big fan of bolts to block off holes.  Very handy.

Observational data:

The problem is red hot soot creating orange red flames.  The presence of soot suggests unburned CO.  This suggests a too rich fuel to air ratio, no?  When I increased the secondary air ports from 3/8s to 7/16ths, this problem was reduced significantly.  When the secondary air ports were even smaller, ¼ inch, the problem was significantly worse.  The orange/red flame problem was also reduced by increasing the depth [width] and height of the combustion chamber.  Better mixing?  Longer residence time?

Any thoughts on this?

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

Cell: (617) 449-8111

google.com/+JockGill

:> Extract CO2 from the atmosphere! <:

Via iPad

> On Apr 8, 2014, at 2:04 AM, Crispin Pembert-Pigott <crispinpigott at outlook.com> wrote:
> 
> Dear Jock
>  
> My only observation is that the draft in the upper section is large and that is going to make the secondary air jets work really well. From experience, the total hole area is a bit large for the diameter and the draft available. That means, were I to measure the O2 level in the exit, it would be well over 10.5% (which is 100% excess air).
>  
> Make a strip with matching holes but only ½ the number and see if it still burns the gases well.
>  
> I often use bolts and push them into the holes to reduce the air supply when testing a new design. Put one bolt in every 3rd hole, for example, to block some of the flow.
>  
> Regards
> Crispin
>  
>  
> Julien,
>  
> A few observations from today:
>  
> 1. The larger the diameter of a TLUD, the larger the volume required for the combustion chamber;
>  
> To this point, I reduced the size of the central column to a one inch pipe that I extended to 5 inches in height - up from three.  This makes the FXJ burner significantly deeper and taller.
>  
> 2. The larger the diameter of a TLUD, the larger the secondary air ports have to be;
>  
> To this end, I increase the size of my ports from 3/8s to 7/16ths of an inch.  One half inch diameter ports would be better.  Hard to drill in a tin can.  Larger airports also reduce the draft on the primary air, which helps control the rate of pyrolysis in operation mode.  Extremely little O2 is required in operation mode, esp. with any pre-heating of the primary air supply.
>  
> 3. Design a TLUD's primary air ports for the oxygen requirements for the middle of the burn, NOT the startup phase.
>  
> To this end, I now start the TLUD over a grate with unrestricted access to primary air.  This supports the higher oxygen requirements during the startup phase.  Additional starter may have to be used at about the 5 - 7 minute mark to complete startup and transition to operation mode.
>  
> Once startup is accomplished, place the unit in its outer can.  In this position, the primary air is restricted by the narrow gap between the bottom of the TLUD and the outer can.  See the photo below:
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