Predicting ignitions of flammable gas mixtures caused by contact break discharges with dynamic source characteristics

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The previous project focused on a multi-physical approach to contact break discharges in H2/air mixtures for constant current sources. An application-oriented model has been developed, which can predict ignition for a reference situation (30 V, 60 mA) in the context of explosion protection. Several experimental and modeling investigations on basic phenomena supported the understanding of underlying mechanisms and are unique in the field of explosion protection. It was shown that, in contrast to spark discharges with minimum ignition energy as ignition criterion, the investigated contact break discharges require a certain power density for a distinct time (ca. 200 µs) for a successful ignition. For this reason with the new project, the investigations are extended to dynamic current sources and the resulting dynamic behavior of the discharge and thus into the ignition-relevant hot gas kernel. The systematic investigation can be performed by varying the power transfer into the discharge and is realized with trapezoidal source characteristics and linear characteristics including a selected set of external circuit parameters. These source types are commonly used in practice. In order to verify the application-oriented model for dynamic source characteristics, it is necessary to analyze and simulate the effects of such characteristics. A 1D collisional radiative model simulation should be extended to a multi-level system of excited states and cadmium should be considered as a fraction in a H2/air mixture. Non-LTE calculations provide thermo-physical data, which will be used as input data in a 2D heat conduction model. This model is going to be extended to moving electrodes and dynamic currents as well and will allow to verify the application-oriented model for more complex situations. Reliability of the models will be further improved by a variation of material parameters using Zn as cathode material. It is also planned to improve the method by a more reliable contact device with drives outside the explosion chamber and an improved optical access for better schlieren diagnostics. The final goal of the project is to adopt the existing application-oriented model to the dynamic behavior of the discharge as well as the above-mentioned model optimizations including a selected set of external circuit parameters.