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

以前的项目集中在恒流源的氢气/空气混合气体中接触断开放电的多物理方法上。开发了一个面向应用的模型，该模型可以在防爆的情况下预测参考情况(30V，60 mA)的点火。对基本现象的几项实验和模型研究支持了对潜在机制的理解，在防爆领域是独一无二的。结果表明，与以最小点火能量为点火判据的火花放电不同，所研究的触头断口放电需要一定的功率密度(约200µS)才能成功点火。为此，在新项目中，研究扩展到动态电流源和由此产生的放电动态行为，从而扩展到与点火相关的热气核。系统研究可以通过将功率转移到放电中来执行，并且利用梯形源特性和包括选定的一组外部电路参数的线性特性来实现。这些源类型在实践中经常使用。为了验证面向应用的动态源特性模型，有必要对动态源特性的影响进行分析和仿真。一维碰撞辐射模型的模拟应推广到激发态的多能级系统，镉应被视为氢/空气混合物中的一部分。非LTE计算提供了热物理数据，这些数据将用作2D热传导模型的输入数据。该模型还将扩展到移动电极和动态电流，并将允许在更复杂的情况下验证面向应用的模型。以锌为正极材料的材料参数的变化将进一步提高模型的可靠性。它还计划通过更可靠的接触装置和更好的纹影诊断改进该方法，该装置带有爆炸室外部的驱动器和改进的光学通道。该项目的最终目标是采用现有的面向应用的模型来研究放电的动态行为，以及上述模型的优化，包括选定的一组外部电路参数。

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.