Hierarchical modeling concepts for ignition processes of fluorinated refrigerants

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The goal of the subproject is to develop a hierarchical mathematical model for the simulation of ignition of fluorinated refrigerants (R32 (difluoromethane), R1234yf (2,3,3,3-tetrafluoropropene), and R1234ze (trans-1,3,3,3-tetrafluoropropene)) under laminar and turbulent conditions. Experimental and theoretical results of the project partners will be used for model validation and model development. The model development is based on detailed numerical simulations, analysis and model reduction for the chemical kinetics and its coupling with molecular transport, and statistical models for the ignition probability. The focus of this subproject is on the initial phase of the ignition process, and in particular on the interaction of the chemical kinetics with molecular transport properties. In particular the following questions will be addressed: What is the influence of the ignition source on the formation of the initial flame kernel? Do reactions of ions have an important impact on the chemical kinetics? Which mechanisms govern flame kernel formation for small ignition radii? Does the low flame propagation velocity of fluorinated compounds change the early stage of the ignition in a qualitative way? Is there a difference between minimum ignition energies for ignition of the kernel and the formation of a self-sustained flame propagation? How important are statistical fluctuations of the ignition kernel formation? In order to answer these questions, detailed numerical simulations will be performed using detailed kinetic mechanisms in combination with detailed transport models for neutral and charged species. In order to focus on the physical chemistry of the underlying processes, and to allow detailed calculations, a focus will be on spatially one-dimensional configurations (including curvature and strain effects), and an extension to two-dimensional configurations will be performed only for a few critical test cases. Furthermore, time scale analyses for the coupled reaction-diffusion system will be performed based on the concept of Reaction-Diffusion-Manifolds (REDIM). This will allow to identify the governing subprocesses and to develop reduced coupled reaction-diffusion models, which are then used for hierarchical statistical models for the ignition process.