Design of a partially aerated naturally aspirated burner for producer gas

This article presents a detailed methodology for the design of a partially aerated naturally aspirated burner used for combustion of the producer gas generated in a downdraft gasifier cookstove. The main difference between an LPG burner and producer gas burner is that the former uses a high velocity jet of gas at ambient temperature whereas the latter uses a low velocity, high mass flow rate, buoyant jet of gas at 100-300 °C. Due to the elevated temperatures, buoyancy force plays an important role in entraining combustion air into the burner for producer gas. This has been accounted for in the new methodology, developed based on the design procedure available in the literature for hydrocarbon fuels. A mathematical model for fluid flow and heat transfer through the burner has been developed to predict percentage of primary aeration in the burner at different producer gas flow rates. The pressure drops predicted by the model have been validated using experimental measurements. The predictions of the model have been used to corroborate the assumptions and heuristics used in the design methodology. The predictions have also been used to demonstrate the importance of considering buoyancy in burner design, by comparing with a burner designed ignoring buoyancy. With the use of the newly designed burner, the thermal efficiency of the gasifier cookstove was found to improve substantially. Carbon monoxide (CO) emissions from the cookstove using this burner were also found to be within the limits (<5 g/MJd) recommended in the Indian Standards for cookstoves.