NUMERICAL INVESTIGATIONS OP THERMOACOUSTIC INSTABILITY IN GAS TURBINE COMBUSTION CHAMBERS HYDROGEN FIRED

摘要

During last decades the more restrictive legislations have constrained gas turbine manufactures to develop innovative technologies for reducing pollutant emissions. In this context, hydrogen can give several advantages: no CO, UHC and PAH are produced by hydrogen combustion. Moreover, if hydrogen is derived as a waste product from an industrial process or if it's produced by renewable energy or by clean technologies, its pollutant impact is mainly limited to NO_X production. Studies on a gas turbine equipped with a diffusive 100% hydrogen fired combustor [1], [2] showed that NO_X reduction based on "Minor Modification" can't allow acceptable NO_X levels. For a further relevant reduction, premixed combustion may be a valid solution. In general, premixed combustors are prone to thermoacoustically induced combustion instability. The aim of this paper is to define numerical methods for the thermoacoustic characterization of gas turbine combustion chambers hydrogen fired. The in-house code INST ID was developed to evaluate the resonance frequencies, their stability and pressure mode shapes. Such code implemented a one-dimensional approach based on lumped parameters and a linear combustion dynamic hypothesis [3] , [4]. The flame response was represented by a simple time lag approach, according to several experimental results [5] , [6] . The time lag was evaluated through the Eulerian method by Krebs et al. [7] . The experimental data performed at the Enel facility of Livorno (Italy) on a premixed combustor prototype designed for CH_4-H_2 mixture up to 100% H_2 supply were available for the validation of the numerical procedure.