An Integrated Approach for Optimal Design of Micro Gas Turbine Combustors

The work presents an approach for the optimized design of small gas turbine combustors, which integrates a 0-D code, CFD analyses and an advanced game theory multi-objective optimization algorithm. The output of the 0-D code is a baseline design of the combustor, given the required fuel characteristics, the basic geometry (tubular or annular) and the combustion concept (i.e. lean premixed primary zone or diffusive processes). For the optimization of the baseline design a simplified parametric CAD/mesher model is then defined and submitted to a CFD code. Free parameters of the optimization process are position and size of the liner hole arrays, their total area and the shape of the exit duct, while different objectives are the minimization of NOx emissions, pressure losses and combustor exit Pattern Factor. A 3D simulation of the optimized geometry completes the design procedure. As a first demonstrative example, the integrated design process was applied to a tubular combustion chamber with a lean premixed primary zone for a recuperative methane-fuelled small gas turbine of the 100 kW class. Both overall geometry and computed performance resulted to be comparable with the ones of a newly designed state of the art combustor prototype, assumed as test-case for the described integrated approach. Significant topics of the research are the demonstration of the usefulness of advanced optimization techniques in combustor design and the preliminary validation of the combustion-emission model, a 2-step implementation of the EDM one, completed with the thermal NOx formation mechanism.