[Stoves] The upside of Down feed

[Crispin Pemberton-Pigott]

Dear Alex

I am just getting round to responding to your very interesting demo burn.

First, what a great idea. It is a demonstration that natural draft can
accomplish the same effect as an electric fan.

Next, a couple of questions. Did the pellets fall into the pipe with no form
of grate of any kind? Just fell into the pipe and the air blasts them along
as they burn?

What is the chimney height? What is the temperature at the top and bottom (I
want to work out the draft in Pascals).

I see a strange bucket thing on the left. What is it? 

Now, on to your comments:

>The other shows it operating  with a burner that has a small unsealed
hopper for pellets. 

I presume they fed unassisted.

>I use a loose lid/follower to ride down on the pellets. 

Was that to limit the air flow or more to make it feed well?

>So far there has been no fumes coming up and out, and the fire has not
chased the air and fuel back into the hopper. 

Critical point. The reasons is I believe, what Dr Tom said to many times:
superficial velocity, perhaps in this case just straight velocity. If the
air passing through the fuel is going fast enough there is not chance the
heat can start pyrolysing the pellets in the hopper.

So my statement about fire following air (i.e. the flames progress toward
the air supply) has to be qualified with a condition that 'below a certain
air velocity'. That may or may not have to do with the superficial velocity
or that plus a figure for the way the fuel pyrolyses. Coal, charcoal and
wood will have different values.

>The bottom throat on the hopper is about 5 cm diameter. It operates
continuously at one speed with an input of 1.6 kg of wood pellet per hour.

That burn rate is perfect for some small homes. It really bears looking at
closely to see if a bolt-on burner can be fitted into some stoves - I am
thinking of a goat dung burner (natural biomass pellets).

The difference between this and a downdraft burner is that the fire is not
at the bottom of the hopper, it is in the tube so technically it is a
hopper-fed cross-draft fire. Seems to me it would work well with corn as a
fuel if you don't get a glass build up.

Do those corn stoves have a wiggling wire worm because of ash issues? Or
just or move the fuel?

Regards
Crispin