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A cycle-resolved two-dimensional flame visualization technique using Mie-scattering from submicron sized smoke particles added to the homogeneous charge mixture of a spark-ignition engine has been developed. This diagnostic technique was applied to a square piston engine with four windows. Pulsed laser sheets were generated by a copper vapor laser at a frequencies of 6 kHz. The light scattered by the smoke particles was collected by a drum camera on high sensitivity photographic film. The flame contours were analyzed using fractal analysis and complex Fourier transform procedures. Radii of curvature, wrinkling factors and turbulent burning velocities have been determined at different engine speeds and equivalence ratios.

The structure of turbulent flames was examined in a square-piston engine. Submicron-sized smoke particles were added to the homogeneous propane/air mixture. The Mie-scattering of these particles allowed to visualize two-dimensional flame contours. A copper vapour laser generated pulsed laser sheets at a frequency up to 12 kHz. The flame contours were evaluated with digital image processing methods: fractal analysis, complex Fourier transform procedure and statistical flame contour analysis. The following flame parameters have been deduced applying these methods: Fourier factor, combustion zone thickness, mean radius of curvature, fractal dimension, wrinkling factor, flame-let crossing frequency, integral length scale and flame front thickness.

Fundamental investigations have been made on processes in common spark plugs useful for ignition of fuel-air-mixtures. Development of spark discharge from the early beginnings as well as the initiation of chemical reaction have been studied experimentally by using very high frequency measuring technique, radiation measurements, spectroscopic methods and interferometry by a nitrogen laser (∼300 ps). The measurements have been carried out in non-reacting gases (N2, air) as well as in inflammable mixtures. A complete description will be given of the total process from the spark breakdown to the arc and glow-phase, resp., in the millisecondrange including temperature, local dimensions, energy distribution and radicals which can be formed.