Natural draft and forced primary air combustion properties of a top-lit up-draft research furnace

Abstract

Worldwide, over four million people die each year due to emissions from cookstoves. To address this problem, advanced cookstoves are being developed, with one system, called a top-lit up-draft (TLUD) gasifier stove, showing particular potential in reducing the production of harmful emissions. A novel research furnace analogy of a TLUD gasifier stove has been designed to study the TLUD combustion process. A commissioning procedure was established under natural draft and forced primary air conditions. A visual assessment was performed and the temperature and emissions profiles were recorded to identify the combustion phases. The efficiency was evaluated through the nominal combustion efficiency (NCE = CO2/(CO2 + CO)), which is very high in the migrating pyrolysis phase, averaging 0.9965 for the natural draft case. Forced primary air flows yield similar efficiencies. In the lighting phase and char gasification phase the NCE falls to 0.8404 and 0.6572 respectively in the natural draft case. When providing forced primary air flows, higher NCE values are achieved with higher air flows in the lighting phase, while with lower air flows in the char gasification phase. In the natural draft case high H2 emissions are also found in the lighting and char gasification phases, the latter indicating incomplete pyrolysis. From the comparison of the natural draft with the forced draft configurations, it is evident that high efficiency and low emissions of incomplete combustion can only be achieved with high controllability of the air flow in the different phases of combustion.