32
CAUTION!
During operation, the secondary air slider
should never be completely closed. In contrast,
however, the fi re box door and ash compart-
ment must always be tightly shut.
9. The Combustion Process
EA piece of wood burns in three phases. In a wood fi re, ho-
wever, these processes occur both consecutively and simulta-
neously.
9.1 Drying Phase
The moisture still remaining in the air-dried wood (approx.
15 - 20%) is evaporated. This takes place at temperatures of
approx. 100°C. For the evaporation to occur, the wood must
be supplied with heat during the warming up phase; this is
achieved by using small wood logs.
9.2 Degasifi cation Phase
At temperatures between 100°C and 150°C, the contents of
the wood start - slowly at fi rst – to disintegrate and gasify and
the wood begins its thermal decomposition. At temperatures
above 150°C, the gas development accelerates. The proportion
of volatile components makes up around 80% of the wood
substance. The actual combustion begins at a temperature
of about 225°C (ignition temperature) with the ignition of
the resultant gases and the release of heat. There must be an
adequate supply of oxygen available for this purpose. The peak
of the combustion process is reached at approx. 300°C. The
reaction process is now so rapid that the largest amount of
heat is released at this point; fl ames can reach temperatures
of up to 1100°C.
9.3 Burn-off Phase
Glowing charcoal embers remain after the volatile componen-
ts have been burned off. These burn slowly, almost without
fl ames, at a temperature of approx. 800°C.
Crucial to a clean and effi cient combustion process is a com-
plete as possible chemical reaction of the wood gases with the
oxygen in the combustion air. In your Hase stove, the combu-
stion air is pre-heated and guided into the fi re box via wide air
inlet openings, so that at high temperatures, there is a good,
thorough mixing of the gases with the air. An important variable
in any combustion phase is the amount of combustion air. Too
little air leads to an oxygen defi ciency and incomplete combu-
stion, while too much air reduces the fi re box temperature and
thus the effi ciency. Incomplete combustion can generate air
pollutants such as dust, carbon monoxide, and hydrocarbons.
Degasifi cation
Drying
Burn-off
fi g. 3
9.4 Expansion Noises
Steel expands upon heating and contracts as it cools. These
movements occur during the warming up and cooling down
phases, as well as when adding fuel. They can cause your stove
to emit audible expansion sounds. However, the design and
construction of your stove takes this into account and prevents
this physical process from damaging the stove.
10. The Chemistry of Wood
Wood predominantly consists of the elements carbon, hy-
drogen, and oxygen. It contains virtually no environmentally
hazardous substances such as sulphur, chloride and heavy me-
tals. As a result, complete wood combustion produces mainly
carbon dioxide and water vapour as the primary gaseous pro-
ducts as well as a small quantity of wood ash as the solid com-
bustion residue. On the other hand, incomplete combustion
can generate a number of pollutant substances, such as carbon
monoxide, acetic acid, phenols, methanol, formaldehyde, soot,
and tar.
11. Contribution to Environmental Protection
Whether your stove burns in an environmentally friendly or
environmentally hazardous manner depends to a large extent
on how you operate it and the type of fuel you use (see Section
9, „The Right Fuel“).
Therefore, use only dry wood; hardwoods such as birch and
beech are most suitable.
Only use small pieces of wood to light the fi re. They burn faster
than large logs and as a result, the temperature required for
complete combustion is reached more quickly.
For continuous heating, adding smaller quantities of wood
more frequently is more effi cient and more ecological.
Summary of Contents for Delhi 124
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