The effects of fuel type and stove design on emissions and efficiency of natural-draft semi-gasifier biomass cookstoves

To assess the effects of stove design and fuel type on efficiency and emissions, five configurations of natural-draft, top-lit up-draft (TLUD) semi-gasifier cookstoves were tested with two biomass fuels.  An energy balance model was developed using measured temperature data to identify the major sources of efficiency loss.  Emissions and efficiency varied substantially with stove design and fuel type, and transient increases in CO emission correlated with refueling.  The highest measured thermal efficiency was 42%.  The lowest CO and PM emissions were 0.6 g MJd− 1 and 48 g MJd− 1. These results fall within Tier 3 for high-power efficiency and emissions and suggest that development of a Tier 4 natural-draft semi-gasifier cookstove is possible. The energy balance illustrates that up to 60% of the energy input as fuel can remain as char once the fuel has gasified. This result suggests that both thermal and overall efficiencies should be calculated when evaluating TLUD cookstoves.