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.

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About the Influence of the Energy Dependence of the Electron Collision Frequency on the Electrical Conductivity of Weakly Ionized PlasmasWith regard to experimental applications in plasma diagnostics numerical approximations are given for the Gurevic-type correction functions, which in the kinetic theory of weakly ionized plasmas describe the deviations from the Lorentzian electrical conductivity. The approximations are based either upon the dependance of the collision frequency on the power of the electron velocity, or on a first order Taylor expansion around the most probable electron velocity of a Maxwellian distribution.For all assumptions regarding the velocity dependance of the collision frequency the influence of temperature (and pressure) on the effective collision frequency is indicated.

In order to determine the electron-molecule collision frequency in an acetylene-oxygen flame (burning within a X-band wave-guide) the decrease of microwave attenuation caused by an increasing magnetic field is being measured. It is shown that this decrease is equivalent to the wellknown high pass character of a plasma. The small attenuation is enlarged by using a Perot-Fabry type waveguide resonator. Nothing has to be known about its properties, since relative attenuation data are used for evaluation only. For the same reason no knowledge of electron concentration is necessary. The collision frequency value is exact within 4%, which is sufficient for excluding Coulomb collision interaction. The comparison with data in the literature is satisfying only, if the collision model of an electron induced dipol is accepted. With this and a flame temperature of about 3350 ~ the collision frequency amounts to 179 + 7 GHz.