Development of numerical tools for the analysis of advanced airblast injection systems for lean burn aero-engine combustors

The liquid fuel preparation has a strong impact on the combustion process and consequently on pollutant emissions. However, currently there are no validated and computational affordable methods available to predict the spray breakup process and to reliably compute the spray distribution generated after primary breakup. This research activity, carried out within the framework of the European project FIRST (Fuel Injector Research for Sustainable Transport), is aimed at developing reliable tools to be used in the industrial design process able to describe the processes involved in liquid fuel preparation in advanced injection systems based on prefilming airblast concept. A multi-coupled solver for prefilming airblast injectors which includes liquid film evolution and primary breakup was developed in the framework of OpenFOAM. The solver is aimed at improving the description of the complex physical phenomena characterizing liquid fuel preparation and spray evolution in advanced airblast injection systems within the context of typical RANS (U-RANS) industrial calculations. In this kind of injectors, gas-phase, droplet and liquid film interact with each other, thus, in order to properly predict spray evolution and fuel distribution inside the combustor, proper tools able to catch the most important interactions among the different phases are necessary. A steady-state Eulerian-Lagrangian approach was introduced in the code together with up-to-date evaporation and secondary breakup models. Particular attention was devoted to the liquid film primary breakup and to the interactions between gas-phase and liquid film. A new primary breakup model for liquid films, basically a phenomenological model which exploits liquid film and gas-phase solutions for the computation of spray characteristics after breakup, was developed and implemented in the code. Different formulations for the computation of droplet diameter after breakup were evaluated and revised on the basis of recent experimental findings. The multi-coupled solver was validated against literature test cases with detailed experimental measurements and eventually applied to the simulation of an advanced prefilming airblast injector based on the PERM concept in a tubular combustor configuration. The proposed approach allows us to better describe the fuel evolution in the injector region leading to a more comprehensive and physically consistent description of the phenomena regulating liquid fuel preparation compared to standard approaches which neglect the presence of liquid film and its interaction with both droplets and gas-phase.