Experimental study on a high efficient and ultra-lean burn meso-scale thermoelectric system based on porous media combustion

Highlights: • A thermoelectric system based on porous media combustion were proposed. • Thermoelectric power generation is achieved under lean combustion condition. • The lean limit is obtained at 0.46, which is the lowest in available literature. • Four layouts of porous media are compared and the highest efficiency is 1.62%. • The downstream porous media functions as a heat sink and redirects heat flux. Current combustion-based meso-scale thermoelectric systems generally operate at stoichiometric ratio, which leads to high emissions. Lean burn is beneficial to the burning of low-concentration gas and emissions reduction. To exploit the thermal energy of low-concentration gas, this paper proposed a meso-scale thermoelectric system based on porous media combustion to reduce the lean burn limit while utilizing thermal energy by thermoelectric generators. Experimental results showed that the lean burn limit is reduced to 0.46 which is the lowest obtained so far. It was found that the relationship between system efficiency and equivalence ratio or inlet velocity is not monotonous, but is related to wall temperature distribution and flame situations. The system efficiency reaches its peak when the equivalence ratio is around 0.70. To improve the system efficiency, four layouts of porous media were proposed. All four layouts are found to be useful to stabilize the flame in a confined position. However, for the same thermal power input, the combustor with the downstream porous media gives higher wall temperature and higher system efficiency because the downstream porous media functions as a heat sink to absorb more heat from the flame and redirects it to thermoelectric generators. Experimental results provided a useful reference for the development of the combustion-based meso-scale thermoelectric system.