Design, Numerical Modeling and Optimization for Experimental Evaluation of Biogas Burner flame-port in ‘Injera’ Baking Stove

Abstract

In Ethiopia, 95% of the population relies on the use of traditional biomass for cooking application (IEA, 2015) among which 50% of the energy is used to bake Injera. Due to the low efficiency of injera baking biomass stoves, large amounts of firewood are used, resulting in high indoor air pollution, greenhouse gas emission and rampant deforestation. The attempts to improve injera baking stove resulted in incremental change in efficiency and reduction in emission of pollutants without breakthrough so far. To support the ongoing injera baking technology improvement, this study has developed and tested a Numerical Modeling and design tool aimed at optimizing flame-port geometry for household biogas fired burner for injera baking. Literature reviews, design manuals, and existing burner investigation were used to come up with an analytical design of six models. Modeling tool consists of a multi-component simulation that incorporates three dimensional CAD designs with chemical kinetics study coupled with Computational fluid dynamics (CFD) and Genetic Algorithm optimization were formulated for comparative se lection and fabrication. Result of Mixing simulation shows that, burner flame-port model (C5-P1) has stable flame velocity and lower port loading. After simple and cost-effective fabrication of the selected prototype using sheet metal of 2 mm thickness, an experimental investigation was conducted by using Biogas Digester from Degitu Hotel at Jimma town. The experimental investiga tion on the burner involves flame type(color), temperature distribution and Gap manipula tion test between the burner top and the Mitad. Result of the experiment is found in close alignment with the modeling prediction for the chosen design. The Burner demonstrated improved temperature uniformity during baking relative to the baseline(previous burner), with the configuration of 2 levels of circular ports additional modification on the burner head exhibiting superior performance. In addition change in secondary air volume, which directly relates to the gap change shows that, for the 2 levels circular burner type 22 mm increase found to be of a critical gap for better performance in injera baking.