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2-dimensional time resolved (200 frames/s) flow field measurements have been made in a transparent SI square piston engine using a movie version of particle image velocimetry (PIV). To this end the beam of a copper vapor laser was formed into a light sheet and was double pulsed with a pulse separation of 50 μs at a repetition rate of 200 Hz. A rotating drum camera was used to record the Mie-scattered signals from seeding particles. The circumferential velocity of the drum of the camera causes an image shifting of the two exposures taken with a double pulse. By proper adaption of drum and engine speed, a series of up to 70 double pulsed images per individual engine cycle may be recorded on film. This film data may be evaluated uniquely with respect to both magnitude and direction of individual flow vectors in the flow field.

A detailed, one-dimensional, time dependend model is presented, describing flame kernel development in spark ignition engines which explicitely accounts for all fundamental properties of the ignition system (supplied electrical energy and power, discharge mode, energy transfer efficiency to spark plasma, plasma temperature distribution, gap width, heat losses to electrodes and chamber walls), of the combustible mixture (pressure, temperature, equivalence ratio, residual gas fraction, laminar burning velocity, type of fuel) and of the flow field (mean flow velocity, turbulence intensity, strain, characteristic time and length scales, flame holder effects). The model is based on the strained flamelet model and predicts kernel growth consistently under virtual all relevant physical/chemical conditions. Model predictions have been verified in extensive studies in an optical engine over a wide range of physical/chemical parameters using advanced optical and laser optical diagnostics.

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.

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 effects of mixture turbulence and mean flow velocity on flame kernel formation in a spark-ignition engine were investigated using a disc-shaped optically accessible side chamber. Three-dimensional flow predictions and LDA measurements were performed to get a better understanding of the flow field in this combustion chamber. Thin wire electrodes were located at a peripheral and a central position introduced into the combustion chamber via the glass windows. High-speed schlieren films at 40 kHz were taken from two orthogonal directions to visualize in detail the formation and development of the flame kernel. The purpose was to gain a better understanding of the interaction of turbulence and flame during the first milliseconds after spark breakdown of a transistorized coil ignition system and a capacitor discharge ignition system. This study shows that the flame kernel is changed by the turbulence at flame radii of O.5 to 1 mm depending on turbulence intensity.