Abstract
In South Africa, human and environmental health
implications from domestic solid fuel combustion have
spurred interest in cleaner alternative sources of energy
and better combustion technologies. Field research
among wood and coal burning informal settlements in
Johannesburg has shown that the most prevalent mode
of combustion is self-made imbaula (brazier) stoves,
manufactured from discarded 20 L steel drums. Such
stoves are made without any measure of performance
optimisation, leading to fuel inefficiency and high
emissions - previous field surveys have indicated that
the number, size and placement of primary and
secondary air inlets (taken as holes below and above the
fire grate respectively) vary over a wide range, starting
from an extreme with no holes below the grate [1].
Researchers at SeTAR Centre, University of
Johannesburg, have set out to develop an enhanced
imbaula, by investigating performance in terms of size
and distribution of primary and secondary air inlets,
and height of grate level. The test imbaulas are
constructed out of standard 20 L drums with a height of
360 mm and diameter of 295 mm. A range of hole
configurations has been designed, from which selected
test configurations are fabricated for experimental
evaluation of thermal and emissions properties, using
the SeTAR heterogeneous testing protocol. The results
indicate that higher hole densities (above and below the
grate) lead to higher power outputs and lower specific
CO emissions, but with lower thermal efficiency.
Further, results indicate that adequate air holes below
the grate (primary air) are more important for proper
combustion in an imbaula; however this should be
synchronised with secondary air in-lets (above the grid)
in order to have congruence of all the performance
criteria. This study should lead to the development of a
set of criteria that can further enhance emissions
reductions and fuel efficiency obtained by top-down
stove ignition methods (Basa njengo Magogo) for
imbaula type stoves.