A Computational Study of a Biomass Cookstove With Forced Secondary Air Injection

The use of solid biomass as a primary energy source for cooking is common to nearly half of the world’s population. Household air pollution as a byproduct of biomass combustion creates powerful negative health impacts related to air quality and a strong influence on our global radiative balance. Despite efforts to improve biomass-fueled cooking technology, many current designs still fail to meet WHO guidelines for air quality and consume excessive fuel. One promising method to improve in both of these areas is through introduction of forced primary or secondary air to the combustion process to increase turbulence, mixing, and velocity. Incorporating computational fluid dynamics to the design process for this forced draft air flow can provide insights into the complex and interconnected thermophysical relationships which, otherwise, would require extensive experimentation. The objective of this work is to provide a preliminary computational fluid dynamics study of a secondary air forced draft biomass cookstove. Thermal efficiency and emissions concentrations are investigated relative to various combinations of secondary air flow rates and injection angles. The results from the case study suggest that thermal efficiency of the cookstove is a function of secondary air injection angle, with optimal angle being a function of the specific air-fuel ratio. Additionally, a design trade-off is evident when comparing the pollutant concentration data and thermal efficiency data. Lastly, analysis of the computational results suggests that large pressure gradients about secondary air vortices in the combustion chamber lead to improved thermal efficiency and more complete combustion. The continued development of this work into an open-source computational fluid dynamics tool is underway.