New secondary air injection strategy in top-lit updraft gasifier cookstoves with extremely low emissions: Insights from detailed CFD modeling

Despite the widespread adoption of clean cooking technologies, 2.1 billion people worldwide still rely on traditional cooking methods that cause harmful emissions and severe indoor air pollution. Top-lit updraft (TLUD) micro-gasifier cookstoves offer cleaner combustion through staged air supply, but their performance strongly depends on air injection design. Thus, this study investigates the optimization of the secondary air injection in a TLUD cookstove to improve burnout and reduce emissions from incomplete combustion. A combined numerical-experimental approach is applied, using CFD simulations validated by ISO 19867-1 laboratory measurements. The influence of secondary air injection on gas-phase combustion, flow mixing and heat transfer to the cooking pot is systematically analyzed for multiple configurations with comparable pressure drops. The results show a clear trade-off between improved mixing and thermal efficiency. Stronger jet penetration enhances oxidation and lowers emissions but shifts high-temperature zones toward the chamber walls, increasing heat losses and reducing efficiency. In contrast, staged secondary air injection with varying hole sizes preserves favorable temperature distributions while maintaining effective oxidation. The optimized design reduces carbon monoxide emissions by 40 % compared to the baseline for softwood pellets, with only a 0.9 % decrease in absolute thermal efficiency.