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<div class="moz-cite-prefix">Its getting cold again, so I'm making
time for the stove again.<br>
<br>
First refinement on my list is to try to provide a fuel / hopper
combination that will not 'bridge' jamming in the hopper causing
the fire to die back for a while until fuel finally falls onto the
grate giving poor combustion for a time.<br>
<br>
My plan is to modify the hopper adding two walls to either side of
the grate (shown in red on the plan) so the hopper is only as wide
as the grate and the mouth through into the combustion chamber.<br>
<br>
I've got a load of ash branches that I'm going to chop into short
lengths (10cm, as wide as the grate) so that they can be stacked
into the hopper in an orderly pile (see side view)<br>
<br>
I am hoping this will help the burner to operate without requiring
frequent grate rattling to get the fuel to self feed onto and down
the grate.<br>
<br>
Anyone got any thoughts on this?<br>
<br>
<br>
<img src="cid:part1.08020904.02090105@vegburner.co.uk" alt=""><br>
<br>
Drawing was made using QCad on Linux Mint. <br>
<br>
<br>
<br>
On 23/03/12 17:34, Darren wrote:<br>
</div>
<blockquote cite="mid:4F6CB413.5020900@vegburner.co.uk" type="cite">Finally
got a chance to write up my further experiences...
<br>
<br>
I replaced the broken glass in the door into the combustion
chamber and I added the shakable grate on top of the original
grate. In order to make this work without some very tricky
welding I had to also install the parts to make the hopper taper
from three sides towards the bridge (and onto the part of the
grate inside the bottom of the fuel hopper), rather than from just
one side as it was previously. With the current design the extra
two sloping sides of the hopper act to keep the shakable grate on
top of the original grate and hold the third sloping side in
place.
<br>
<br>
I chopped some very dry recycled pieces of pine timber into
approximately inch by inch and a half 'cubes' and ran the stove
with this. This worked quite well. Approximately every 15 minutes
I could see the fire beginning to die back considerably. I would
then shake the grate and it would flare up again. From my
observations it looked as if this might in part be due to the fire
having burnt back up the grate so that there were only embers on
the part of the grate under the hopper or possibly because the
fuel was bridging in the hopper - shaking the grate also moves the
tapered sides of the hopper and is likely to encourage any fuel
bridge in the hopper to collapse. I noticed after this die back,
once shaken and the fire started to flare up again that there
would be a considerable amount of visible smoke from the chimney
for some time. This led me to believe that I was getting bridging
in the hopper.
<br>
<br>
Next I cut a piece of plate metal to sit on the back part of the
grate and cover about half of the part of the grate that is under
the combustion chamber. I also extended the chimney from 2 meters
to 3 meters.
<br>
<br>
I ran the stove again a couple more times, these times the wood
was probably 2 inch by inch and a half 'cubes'. I had not
intended to cut the wood bigger but preparing the wood was time
consuming and once I had finished I noticed that the 'cubes' were
consistently bigger than on the previous occasion.
<br>
<br>
On both these burns the stove appeared to run similar to the
previous occasion.
<br>
<br>
Next I managed to get my hands on some recently cut ash branches.
Ash has a very low water content and burns reasonably when freshly
cut. I put these branches through a tree surgeons wood chipper.
I loaded the hopper with this and started the fire on the
combustion chamber side using small 'cubes' of dry pine and paper.
<br>
<br>
I ran the stove like this on three occasions. The stove appeared
to 'work' reasonably well. It gave a higher heat output and did
not require shaking, although I did notice at times the fire would
die back a bit, but it would self remedy. I think that this was
probably fuel bridging that would collapse by itself. I did
notice that at times there would be visible smoke from the chimney
- I'm guessing this was after fuel bridging collapse.
<br>
<br>
Burning the chip was however providing a much higher heat output
than I require. I'm not sure how best to try to reduce this
output and keep the stove burning efficiently.
<br>
<br>
I think I need to try and address fuel bridging but I'm not sure
how best to do this - nor am I sure what type of fuel is going to
work best.
<br>
<br>
I can get lots of wood chip although generally the water content
is likely to be too high - and I cant think of an easy way to dry
the wood chip.
<br>
<br>
I was thinking about laying up a lot of 1-2 inch diameter branches
to season that I could then saw to 1 inch lengths. I could get
some seasoned wood and put it through a wood chipper - although I
do not always have access to a chipper and would prefer not to be
dependant on access to such a machine for my fuel.
<br>
<br>
I was wondering how best to modify the hopper design. As the
sloping sides guide the fuel onto the grate, if they were not
there I'm thinking that they would, in effect, be replaced by
unburnt fuel as air will not be flowing through these areas???
Unless I reduce the hopper area so that it has upright sides going
straight up from the grate. This would however seriously reduce
the amount of fuel that the hopper holds (and would be somewhat
disappointing)
<br>
<br>
The stove was getting through the fuel more quickly than I
expected - I guess that I can address this by reducing the burn
rate (and the output) which would be a double win for me, as long
as the stove would still burn efficiently.
<br>
<br>
I currently have a butterfly valve in the primary air inlet - can
block the secondary air inlets (although this appears to have
limited effect on combustion) I intend to fit some kind of valves
to these. I also intend to add a butterfly valve in the bottom of
the chimney.
<br>
<br>
I wont be able to do any more testing/make more refinements for a
while but thought I would give a (late) update before the details
had escaped me.
<br>
<br>
Best
<br>
<br>
Darren
<br>
</blockquote>
<br>
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