A numerical investigation is carried out to study ignition events of different premixed stoichiometric fuel/air mixtures by hot exhaust gas jets. The simulations are performed for premixed, stoichiometric hydrogen/air, ethylene/air and propane/air mixtures in configurations relevant to safety applications. The ignition events of the different fuel/air mixtures by their corresponding exhaust gas jet are examined qualitatively analyzing processes and conditions leading to ignition. A stand-alone probability density function (PDF) method in connection with a projection method (PM) to calculate the mean pressure is used to model the turbulent flow. The transport equation for the joint velocity – turbulent frequency – scalar PDF is solved by a Monto Carlo/particle method. In order to reduce the computational costs concerning the chemical kinetics the reaction diffusion manifolds (REDIM) technique is used to get an appropriate reduced kinetic scheme.

Spark ignition by low-energetic electrical discharges in combustible fuel/air mixtures is a significant safety risk in various industries. In the present paper, OH-LIF measurements and numerical simulations of the ignition and early flame propagation of hydrogen/air, propane/air and ethene/air mixtures are reported. The experiments, carried out at four energy levels close to the respective minimum ignition energy (MIE), show that higher energy input leads to a wider flame radius, which is in agreement with one-dimensional numerical simulations. Further, the evaluation of the radial OH distribution reveals the highly stochastic nature of this process if the introduced energy is near the respective MIE. By utilizing the combined methodical approach of experiments and simulations, the key factors impairing the experimental repeatability are identified. The numerical results indicate at lower energies a longer time delay between source time and ignition, during which loss processes and perturbations may lead to extinction. One important influencing factor is the three-dimensional flow induced by the discharge, effectively increasing the experimental scatter. The presented work facilitates a detailed view on the complex physiochemical mechanisms dominating ignitions of explosive gas mixtures by low-energetic electrical discharges.

Die Einführung von Wasserstoff als sicherer Energieträger braucht eine robuste Wissensbasis, darauf aufgebaute Werkzeuge zur Auslegung und Sicherheitsbewertung von Wasserstofftechnologien und ein international harmonisiertes Regelwerk. Viele der innovativen Technologien implizieren Wasserstoff bei hohen Drücken und/oder kryogenen Temperaturen, mit denen in verteilten Anwendungen erstmalig private Nutzer in Kontakt kommen. Um überkonservative, teure Sicherheitslösungen zu vermeiden, gleichzeitig aber die Einsetzbarkeit und Sicherheit von Wasserstoffanwendungen zu demonstrieren und die Akzeptanz für die Technologie aufrecht zu halten, muss auch die Sicherheitsforschung mit den Trends der technologischen Entwicklung Schritt halten, oder sie besser noch antizipieren. So beschreibt dieser Überblicksartikel nicht nur den gegenwärtigen Stand der Kenntnisse und Technik bezüglich Wasserstoffsicherheit, sondern auch ihre Weiterentwicklung.

The ignition of combustible/air mixtures by electrical discharges includes several physical and chemical processes. In process safety often the total available electrical energy is taken as a risk measure. However, to get a more detailed insight in the ignition process, also energy losses to the surrounding have to be considered. Additionally, for specific discharges not only the dissipation leading to thermal heating is of importance. Especially in the case of non-equilibrium plasma, a specific fractional amount of the discharge energy is used for electron impact dissociation, excitation, and ionization reactions, producing active radicals and ions during the discharge phase. While the electrical energy can be measured easily, it is difficult to determine energy losses. In this paper three different electrical discharges are examined experimentally and numerically to yield a better understanding of the ignition by electrical discharges.

Experimental investigation of a partially premixed flame stabilized in a combination of bluff body and swirling flowfields is reported. Simultaneous measurement of 2D fuel distribution (Acetone-PLIF) and flame structure (OH-PLIF) are performed with varying thermal power. Two flame stabilization modes – swirl influenced conical shaped, and, bluff-body influenced toroidally shaped – are observed in OH chemiluminescence measurements. Upstream propagation of the flame with decreasing global equivalence ratios is noticed, with the flame being transferred from the swirl-influenced to the bluff body influenced flowfields. The average flame stabilization location in both modes is found to be approximately close to the stoichiometric surface with the flame base oriented toward the inner shear layer. The degree of fuel/air mixing calculated from Acetone PLIF images by determining the unmixedness shows that the stabilization locations overlap with regions of perfect mixing. The swirl-influenced flames are stabilized at the farthest distance from the burner exit, with the flame base closer to the stoichiometric surface, whereas the bluff body influenced flames oriented along the stoichiometric surface in the inner shear layer.