Development of wood-burning rocket cookstove with forced air-injection

摘要

Nearly 40 of the world's population still relies on biomass stoves as their primary cooking source. Indoorcooking with biomass stoves produces harmful emissions such as fine particulate matter (PM_(2.5)) and canresult in significant cardiovascular and respiratory disease. Air injection technology, in the forms of over-fire,under-fire, and staged (a combination of under- and over-fire), has been used for decades to reduce emissionsinsmall-scale industrial biomass burners. Recently, researchers have begun integrating air-injection into biomasscookstoves, but the number of studies is limited, and improper air-injection can result in worsening stove performance.In this paper, we develop and analyze three wood-burning biomass rocket stove air-injection strategiesusing computational fluid dynamics and experiments. We consider over-fire and under-fire air-injection independently,and then develop a staged air-injection system that combines the optimal jet characteristics fromthe purely over-fire and under-fire systems. Results showthat significant performance gains, both in terms of reducedemissions and increased burn-rate are achievable with forced air-injection. For a radial over-fire air injectionsystem, jet momentum flux is found to control fuel and air mixing and is the driving metric for reducingparticulate emissions. For the under-fire system, excess air ratio was found to control both the emissions rateand firepower. In a comparison of all three air-injection strategies, over-fire air injection was found to have thelargest reduction in emissions, under-fire air injection had the largest increase in firepower and reduction in boilingtimes, and the staged air injectionmethod achieved both improvedemissions and burn-rate. Additionally, thecombustion start-up phasewas observed to account for the majority of emissions in all forced-draft stoves, and ismost sensitive to under-fire injection, remaining an area ripe for improvement.