Influence of chimneys on combustion characteristics of buoyantly driven biomass stoves

The vast majority of people in the developing world burn solid fuel in basic cooking structures, many of which have no vent, flue, or chimney to remove air contaminants from the indoor environment. Chimney stoves are often investigated as a solution to ensure proper ventilation. This work looks beyond chimneys as a vent pipe; chimneys have the potential to influence the combustion characteristics of biomass from a natural convection (no external power) driven stove. Experimental work as well as chemical kinetic modeling results suggest that a chimney plays an active role in the performance of a biomass stove by influencing the overall air-to-fuel ratio and subsequently the production of carbon monoxide. Two different stoves, operated at multiple wood consumption rates, were shown to run with steady state excess air of 300% - 1250% in all cases. The wood consumption rate was found to be independent of the pulling capacity (draft) of the chimney for either stove. Increasing draft, through the addition of chimney sections, was shown to increase excess air. In this case, draft serves only to cool combustion gases through dilution of flue gas with excess air. Increasing excess air was shown to decrease modified combustion efficiency in experiments and chemical kinetic modeling. Actively increasing the frictional loss coefficient of a chimney by decreasing the internal diameter was shown to reduce CO production from one stove through a reduction of excess air.