Optimisation of ventilation and ignition method for reducing emissions from coal-burning imbaulas

Despite more than 87% households in South Africa being electrified, domestic coal combustion still remain a major source of cooking and heating in low-income households on the Highveld. A majority of low-income households burn coal in informal braziers-imbaulas-constructed from 25 L metal drums with holes punched around the sides. These imbaula stoves are hand manufactured without any standard reference with respect to number, size and location of ventilation holes and position of the fuel grate. These devices tend to have poor combustion efficiencies, leading to high emissions of particulate matter and pollutant gases, affecting both indoor and ambient air. This paper focuses on a range of community designed imbaulas and ignition methods (top and bottom lit), with the aim of evaluating thermal and emissions performance using the SeTAR Centre Heterogeneous Testing Protocol (HTP). Three stoves were evaluated, differing primarily in the total area of the ventilation holes. Results show that the stove with largest area of ventilation holes emits less particulate matter, has improved combustion efficiency - CO:CO₂ ratio (4%) and consumes less fuel compared to two other test stoves with smaller areas of ventilation holes. For all stoves tested, the top-lit ignition method showed an 80% reduction in particle emissions compared to the bottom-lit ignition method. From this work, it can be argued that a balance between primary and secondary air inlets and grate height will improve imbaula performance.