[Stoves] Vegetable oils

[Crispin Pemberton-Pigott]

Dear Peter

 

Good to hear from you, I was thinking of you last week testing a downdraft
stove using chunks of wood the same size you use on your DD BBQ (barbie).
The chunks of wood provide quite a bit of excess air so the way the heat
transfer takes place it affected a lot.

 

>As far as I know the difference between kerosene (paraffin) and higher
hydrocarbon fractions, including vegetable oils is the fact that they are
not distillable under atmospheric pressure.

The stove must work then by boiling something in the veggie oil that boils
at a temperature achievable in the evaporator tube. Perhaps that is why
there is so much gunk left behind. A completely different approach (and an
old one) is dripping oil onto a flat plate that is completely contained
inside the combustion chamber. People burn old engine oil that way, and for
similar reasons.

>Undistillable hydrocarbons are fed into the fire as a spray of very fine
droplets that burn completely. 

With the residence time in the flame matching the burnabilty of the droplet,
right? When a droplet of diesel burns, has it been evaporated by radiant
heat under that increasing pressure of the pressure wave?

The same could be done with vegetable oils at the combustor end. However,
most vegetable oils tend to react slowly with oxygen to form gunk which
eventually blocks the passages it has to flow through.

Is this process dramatically accelerated by heating the oil? In other words,
is the depositing cause by O2 already in the fuel? That bodes badly for the
future of burning raw oil.

So for a stove that burns vegetable oil, the piping from the storage to the
burner should be of very simple shape and easy to clean.

Daily, as I understand it.

Realising that producing a spray of fine droplets is out of the question for
domestic stoves, we have to find something that feeds the oil to the
combustion zone where the carbon, resulting from the decomposition of the
oil is burnt as well. 

How about using one of those spinning disks with a spiky periphery that are
used in greenhouses to make as fine a mist as possible? They are very small
(50-75mm) and use only a small amount of power. It is conceivable they could
be driven by electricity, heat or draft.

Possibly something like a perforated disk where the oil burns in updraft
mode and where the holes occupy a sufficient part of the disk area that all
the char comes in contact with air.

Good idea. A variation on the drop-onto-plate idea might do.

Does the Protos stove have any relation to Siemens. 

Yes it is a Bosch-Siemens product.

Regards

Crispin

 

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