Modeling Ultra-lean Superadiabatic Combustion in Multi-scale Porous Burner with Augmented Heat Recirculation and Preheating

Abstract

A novel design of porous burner using an external preheater combined with internal heat recirculation and radiation corridors is presented to utilize the superadiabatic temperature at the combustion zone and explore the combustion of ultra-lean mixtures. The flammability limit of lean mixtures is greatly extended to extremely lean mixtures of equivalence ratios less than 0.2. Utilizing internal and external heat recirculation along with the radiation corridors not only the flame is sustained at ultra-lean mixtures but also provides a means to anchor the flame and exploit the non-thermal equilibrium between the solid and gas phases of porous material. Moreover, the burner operates at temperatures below the metallurgical constraints such as melting points of common metallic materials that can be used as the solid phase of the porous structure to enhance the heat recirculation and further explore the ultra-lean limit. Also low flame temperature results in a low pollutant emission. A three dimensional analysis of the superadiabatic porous burner is analyzed. Thermal efficiencies higher than 50% is presented.