Experimental and numerical investigation of a micro-CHP flameless unit

A numerical and experimental investigation of a system for the micro-cogeneration of heat and power, based on a Stirling cycle and equipped with a flameless burner, is carried out with the purpose of evaluating the system performances with hydrogen-enriched fuels. The numerical model of the combustion chamber gave significant insight concerning the analysis and interpretation of the experimental measurements; however it required considerable efforts, especially regarding the definition of proper boundary conditions. In particular a subroutine was developed in order to couple the oxidation process to the overall operation of the micro-cogeneration unit. This procedure was proved to perform satisfactory, providing values of the heat source for the Stirling cycle that lead to expected thermal efficiencies in agreement with those indicated in the literature for similar systems. The importance of a proper turbulence-chemistry interaction treatment and rather detailed kinetic schemes to capture flameless combustion was also assessed. A simple NO formation mechanism based on the thermal and prompt routes was found to provide NO emissions in relatively good agreement with experimental observations when applied on thermo-fluid dynamic fields obtained from detailed oxidation schemes.