Hybrid draft direct-combustion with secondary air jets in cross-flow for reducing CO and PM2.5 emissions in biomass cookstoves

Abstract

CO and PM2.5 emissions in household biomass cook stoves are affecting billions of lives and millions are suffering from related fatal diseases. An air supply configuration was proposed and tested experimentally to reduce emissions from a prototype biomass cook stove. The hybrid draft staged combustion with primary air by natural draft and preheated secondary air by forced draft was tested in a wood-burning cook stove. The secondary air jets were arranged in cross-flow to the primary flue. A mathematical model to predict the performance of a hybrid draft cook stove was developed and validated experimentally. The effect of different parameters such as excess air ratio (λ), Primary air to secondary air ratio (PA/SA) and Momentum flux ratio (J) was investigated. All three variables have shown a profound effect on CO and PM2.5 emissions. Optimum values of these parameters for minimum CO emissions were identified as λ = 3, PA/SA = 1.9 and J = 94 respectively. However, the mechanism of CO and PM2.5 destruction was found to be different and no such optimum was identified for PM2.5 emissions. The hybrid draft configuration resulted in a significant reduction of CO and PM2.5 emissions, achieving emissions performance corresponding to the Tier 4 level.