[Stoves] The Art of Using Grass Bundles in TLUD Stoves

[Crispin Pemberton-Pigott]

Dear Julien

Crispin offered me the following advice for burning wheat straw in a
gasifier cookstove:

> "It sounds like you could afford to reduce the primary air supply. If you
have things right you should be able to turn it off completely. If you are
able to generate a condition that is primary-air-starved, you can then
regulate it."

>Following that advice, I packed the paint can with as much straw as I
could.  I put the can on top a paint-can lid which blocked off all primary
air.  

That is a good example of total control.

Now you can make a controllable hole that allows you to admit a lot of air
(whatever that means) to get it lighted and then restrict it to an
appropriate level. The result will be continuous gas production.

How much air later? At that size I would guess 1 or 6 holes 6mm diameter but
Paul Anderson should comment here. He built these 10 years ago and have
little tubes coming out the side with several small holes which he could
close individually with tape.

The point is to explore the relationship between primary air supply and the
production of burnable gases.

Because the weather is still cold it is hard to know if what you were trying
to ignite was steam (or how much was steam) and how much was smoke. If it
was not pyrolysing at a high enough rate the secondary air may have diluted
it below the concentration needed for ignition.

The news is that you went from a 5 minute burn to more than an hour. Next
you need to get the burn you want which will be in between. The primary air
supply is all the difference. The secondary air needed depends on the gas
production rate.

It is not all that complicated. The vast majority of stoves have far too
much excess air at the primary and secondary level so the first thing to get
a grip on is the air/fuel ratio (just like a car engine which is why
combustion analysers report the air/fuel ratio).

Regards
Crispin