Characterization Of a Premixed Gas Turbine Injector for Light-Duty and Low Emissions Applications

Recent trends in gas turbine combustor design aim at lowering pollutant emissions through the usage of lean premixed solutions that allow for controlling the fuel mixture and the temperature field. Modern injector combustor systems guarantee low levels of NOx emissions thanks to the employment of premixed and swirl stabilized flames. Such kind of solution must be designed also considering the possible use of hydrogen as fuel, thus abating emissions further. Unfortunately, this type of technology is significantly more susceptible to flashback and instability when switching to hydrogen blends. For that reason, it becomes necessary to correctly characterize the injection system before considering any possible redesign at the industrial level. In this research, a premixed injector for light duty applications, with a relatively limited net power of around 5MW, is investigated through experimental and numerical analysis. In the experimental campaign, consisting of a series of flow tests in quiescent air, the mass flow rate associated with different expansion ratios is evaluated in terms of the equivalent area of a calibrated orifice. The obtained data are used to construct and validate the numerical fluid dynamic models. First, the 1D model is developed with AxSTREAM NET by fitting the available experimental data through calibrated losses in an equivalent geometrical setup and is used to obtain quick and reliable information on the mass flow rates and pressure levels at different points of the gas circuit. Second, a set of 3D CFD simulations is performed with the ANSYS FLUENT solver to achieve a higher level of detail in terms of fluid dynamic characterization. In that case, the injector domain is split into two parts, the pilot and the main and the two components are analyzed by varying the expansion ratio in quiescent air to validate to numerical approach by matching pressure levels and mass flow rates. Moreover, due to the complex geometry of the main part, the main fuel circuit is divided further into two components to reduce the computational cost, then the characterization is based on an iterative procedure. The grid dependence ensures that no effect of the spatial filter is present, whereas the validation against experimental data with a maximum error of around 5pc for the pilot geometry allows for obtaining fundamental preliminary information for the creation of reacting simulations setup or to proceed with the redesign of part of the injection system using additive manufacturing techniques to reduce component cost.