Ignition by electrical discharges
Project 5 is focused on the experimental examination of ignition by electrical discharges with respect to safety assessment in hazardous areas. In the first period, two important types of electrical discharges – non-equilibrium plasmas due to streamer discharges and thermal plasmas – shall be examined.
The energy of an examined electrical discharge is always near the minimum ignition energy. Using optical emission spectroscopy, detailed information about the temporal evolution of atomic oxygen and rotational and vibrational temperatures of molecular nitrogen can be yielded. Time and spatially resolved laser-induced fluorescence measurements of OH radicals will be performed yielding four subsequent images during one single ignition event. Hence, detailed information about flame kernel growth and flame velocities can be derived. In the case of ignition by non-equilibrium plasmas detailed examination of atomic oxygen using two-photon absorption laser-induced fluorescence will be used to examine the temporal evolution of this radical in the ignition volume. All these experiments are necessary a) in the case of thermal plasmas to determine the thermal losses towards the electrodes and b) in the case of non-equilibrium plasmas to develop a kinetic scheme of the chemical processes by streamer discharges.
Along with numerical simulations of these processes useful information about the ignition process induced by electrical discharges will be yielded.
Scientists
| Project leader |  Dr.-Ing. Detlev Markus |
| Researcher |  Stefan Essmann |
Publication single view
Title: |
Characterization of the ignition by repetitive streamer discharges using laser diagnostics |
|---|---|
| Author(s): | , , , and |
| Journal: | J. Loss Prev. Process Ind. |
| Year: | 2012 |
| Volume: | 26 |
| Issue: | 2 |
| Pages: | 324–328 |
| DOI: | 10.1016/j.jlp.2011.10.002 |
| Abstract: | Repetitive streamer discharges caused by transients, e.g. due to high frequency overvoltages, can ignite combustible mixtures, which has to be taken into account concerning the safety assessment of electrical apparatus for usage in hazardous areas. Hydrogen/air mixtures were ignited inside a closed vessel using a rod/plane electrode configuration. Alternating voltage with a frequency between 600 and 750 kHz and amplitudes of up to 20 kV was used to produce streamer discharges. The ignition process and the subsequent flame front propagation were examined with respect to mixture composition and several electrical parameters using time-resolved measurements of planar laser-induced fluorescence (PLIF) of OH radicals. A multiple pulse laser and detection system was used to assemble four images during one experiment. These measurements have given detailed information about the point of ignition and flame velocities. The experimental results will be used to validate numerical simulations of ignition by streamer discharges, which will yield deep insights into this specific ignition process. |