Electric power generation from combustion in porous media

Abstract

Combustion of lean air/fuel mixtures in an inert porous medium provides an efficient way to convert chemical energy of hydrocarbons into thermal energy. The porous medium effectively redistributes the heat allowing the reacting mixture to be preheated before the combustion front. For a lean propane/air mixture (equivalence ratio F ~ 0.6), the combustion front is steady and the combustion temperature is subadiabatic. At lower equivalence ratios the heat wave in the porous media and the combustion front can move synchronously downstream developing superadiabatic temperatures. This superadiabatic effect allows to operate at the range of ultralean mixtures (F ~ 0.1). Thermal energy generated by the combustion process can be converted into electricity by thermoelectric modules (TEMs). In this work, a cylindrical porous burner is designed to absorb the heat of combustion of lean propane/air mixtures. The burner is inserted in a rectangular steel block. The surface of the block is covered by a set of operating TEMs. Confining the combustion front is stabilized by using porous media with different pore sizes. Temperatures are recorded in different regions of the burner by using surface and immersion thermocouples. Adjusting the equivalence ratio, the flow rate of the gaseous mixture, the properties of the porous media, and the TEM characteristics, a quasi-static burn rate is achieved with the surrounding surface at the nominal temperatures required by the TEMs. The maximum electrical power of 9.42 W and the overall conversion efficiency of 2.93% are reached with a voltage of 5.93 V and a current of 1.59 A using a setup of four TEMs electrically connected in series.