Numerical investigation of a swirled flame model combustor fed with pyrolysis gas

This paper describes the numerical investigation carried out to analyze turbulent non-premixed syngas-air swirled flames occurring inside an experimental combustion chamber. The aim of this study is to investigate the flame behaviour and the reduction of pollutant emissions for microturbine operation. The CFD analysis, performed with a commercial code, have been carried out to study this combustion process modelled adopting both RANS and LES approaches. In particular, the first part of investigation is focused on the identification of chemical kinetic reaction mechanisms that can better represent the chemistry of syngas-air combustion in the framework of Laminar Flamelet Model. The considered syngas is a pyrolyzed biomass derived gas, composed mainly of CH4, CO, H2 in different proportions. Several kinetic reaction mechanisms capable of modelling the chemistry of methane, high hydrocarbons and hydrogen simultaneously have been examined in the RANS simulations. The second part of this work concerns a deeper investigation with Large Eddy Simulation technique. This numerical approach analyses the flow field more accurately and permits to obtain temperature and emissions distributions more in agreement with experimental results. The paper describes the LES simulation settings, using the Smagorinsky sub-grid scale model and a proper definition of the temporal computational parameters. RANS and LES results, obtained with different kinetic mechanisms, are finally compared with experimental data performed on the combustion test.