CFD analysis on NOx emission reduction of a diffusive flame gas turbine combustor through water injection

The present thesis object is to evaluate the reduction of nitrogen oxides (NOx) emissions through water injection in a heavy duty gas turbine made by EthosEnergy Italia, using Computational Fluid Dynamic (CFD) analysis. The results will be used to improve the current way water injection is performed in the company gas turbines. The purpose is firstly to improve an already existing CFD combustor model in order to get better agreement on NOx emissions, on temperature and on velocity profiles between real measurements and computed ones. Then, the CFD combustor model is modified by a water injection implementation which allow to study the effect of water for NOx emission reduction. Since the computational effort on describing the water injection spray using Volume of Fluid approach (VOF) is very demanding, a simple approach which consider water injection like a simple heat sink is proposed. In this way the effect of heat extraction made by water evaporation, which is the responsible of NOx emission reduction, is the same as the real one. Nowadays environmental legislation on the emission of nitrogen oxides for gas turbines became harsher all over the world, so a study to reduce NOx emissions became of crucial importance for the company. CFD simulation are done using Converge, which is an innovative software for simulating three-dimensional fluid flow. Converge software features truly autonomous meshing, which allows to save time because it is needed just the geometry model implementation. As a conclusion, results coming from CFD simulation are proven to be accurate on describing the emission level.