The thermal and emission performance of a novel wood-burning cookstove

Abstract

Indoor air pollution from burning solid fuels on makeshift stoves and open fires in low-income households is a significant health concern, causing respiratory illnesses, heart disease, and cancer. According to the World Health Organisation (WHO), this leads to 3.2 million premature deaths worldwide each year. In South Africa, poor socio-economic conditions and limited access to electricity drive the dependence on solid fuels, making exploring cleaner and more efficient cooking technologies essential. This study evaluates a novel wood-burning stove, the Flamingo™ stove, designed to reduce emissions and increase fuel efficiency. A novel feature of the stove design is an integrated oven and a deflecting plate (or flap) that allows two configurations: oven in use and oven not in use. The performance of the stove was evaluated using four common South African wood species: Sickle Bush (Dichrostachys cinerea), Mopane (Colophospermum mopane), Leadwood (Combretum imberbe), and Black Wattle (Acacia mearnsii). Initially obtained as firewood logs, the wood species were cut into 15 x 15 x 250 mm cuttings to fuel the stove, which was initially designed to utilise twigs. The Heterogeneous Testing Protocol (HTP) was employed to replicate real-life cooking conditions, with key performance indicators determined using thermocouples, gas analysers, and particulate matter monitors. Sickle Bush showed the fastest burn rate and the highest firepower, 4.1 ± 0.8 kW, while Leadwood showed the lowest firepower output at 2.8 ± 0.3 kW. Temperature trends varied by species; Sickle Bush exhibited the highest fuel bed temperature, unlike Leadwood, which showed the lowest burn rate and fuel bed temperature. The highest effective thermal efficiency was seen from Black Wattle, showing a low power phase efficiency of 26.2 ± 9.3%. The four local wood species showed emission factors comparable to those in previously reported studies. (Bentson et al., 2022; Deng et al., 2022; Huangfu et al., 2014; Makonese & Bradnum, 2018). NOx and SO2 emission factors shown by the Flamingo™ stove ranged between 0.08--0.13 g/MJ and 0.04-0.13 g/MJ, respectively. The highest CO2 emission factor was from Leadwood, 103 ± 4.0 g/MJ; the remaining three species showed lower 91-95 g/MJ values. PM and CO emission factors between 0.06-0.11 g/MJ and 3.1-4.1 g/MJ were observed, comparable to other cookstove models. The faster-burning species showed increased CO/CO2 ratios due to higher degrees of incomplete combustion. The four species showed good emission performance (Tiers 3-4) but performed poorly on thermal efficiency (Tiers 1-2). Black Wattle showed the best overall performance--Tier 4 for CO emissions, Tier 4 for PM emissions and Tier 2 for thermal efficiency. The use of the oven had a minor influence on the stove's thermal efficiency, showing an increase of up to 5% when the oven was in use. The effective thermal efficiency of the species over the separate phases ranged between 11.7-29.9% when the oven was in use. As slight differences show, the oven did not significantly influence the emission factors, possibly due to experimental uncertainties. Tier performance changed slightly when the oven was used, with an increase from Tier 1 to Tier 2 for thermal efficiency by both Sickle Bush and Mopane. The study highlighted that different wood species significantly impact stove performance, making the choice of wood dependent on the user's specific needs.