[Stoves] secondary air thru a subsurface feed

[Crispin Pemberton-Pigott]

They don't clog.  Try it.

Crispin

 

____

Interesting design idea  Crispin but how does the cook  keep the holes from
clogging? 

Richard 

 

 

On Jul 11, 2014, at 6:22 PM, Crispin Pemberton-Pigott wrote:





Dear Kirk

 

I appreciate that you are working on a common TLUD need and are willing to
share what you can discover. Flameouts are a common problem particularly at
the end when there is still a possibility of there being significant smoke
from the remnant volatiles.

 

One of the activities noticeable at a TLUD convention is inventors tossing
just-struck matches into a smoke bomb to re-establish the flame.

 

My own cure, after creating enough smoke to hide my embarrassed face, was to
conduct the combustion of the gases as close as possible to the upper
surface of the fuel.

 

This turned out to pretty much solve the problem because the secondary air
entrance is low enough to the fuel that it keeps the top hot. This is not in
line with many designs which have a gas burning zone that is away from the
fuel. In my current view the move down burns some of the char and the
payback is a product people are willing to use because the flame is
reliable.

 

There is a new stove which was designed in Mongolia and produced in China
that was submitted to the UB-CAP lab for testing which has what I consider
the 'right' approach. The fuel bed is about 320mm deep which is typical of
the breed. The secondary air is provided through very small holes (maybe 4
or 5mm diameter) around the ceramic combustion chamber. They are at least
125mm below the top of the fuel, were the available space to be completely
filled. The secondary air is preheated to a high degree and limited in
volume by a restricted entrance.

 

It is extremely clean-burning. It has no controls at all - it just runs and
burns out. The PM2.5 reduction against the baseline is over 99%.

 

I have used the same approach and recommend it. Secondary air should not be
spread out over the fuel chamber, not vertically at least. It should be
lower than the fuel top when ignited as it serves little purpose right at
the beginning. The fuel shrinks considerably as it burns and drops to
uncover the ports which are not blocked in the meanwhile, they allow air to
enter, but later they are clear of the fuel.

 

In the end the flame is hot enough to brighten and maintain a hot upper
surface that resists the flameout at the tail end.

 

Regards

Crispin

 

 

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