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In order to facilitate the analysis of SI engine combustion phenomena, we have developed a fiber optic system which allows the observation of combustion in essentially standard engines. Optical access to the combustion chamber is achieved with micro-optic elements and optical fibers in the cylinder head gasket. Each fiber views a narrow cone of the combustion chamber and transmits the light seen within this acceptance cone to the detector and recorder unit. A large number of such fiber optic detectors have been incorporated in a cylinder head gasket and this multichannel system was arranged in a geometric configuration which allowed the reconstruction of the spatial flame intensity distribution within the observed combustion chamber cross-section. The spatial information was gained from the line-of-sight intensity signals by means of a tomographic reconstruction technique.

An optical imaging technique has been developed which allows the visual observation of fuel vapour within selected planes in optically accessed combustion chambers of Spark Ignition engines. The technique utilises fluorescence radiation of hydrocarbon molecules to image fuel vapour distribution. This fluorescence radiation is induced by a pulsed laser light sheet projected into the transparent combustion chamber and it can be observed with an intensified camera gated synchronously with the pulsed laser at any selected time instant of the engine cycle. In addition to recording mixture distribution, the camera arrangement also allows visualisation of the gasoline flame propagation. These imaging methods are used for he investigation of mixture formation and flame development in a transparent, disc-shaped combustion chamber under low speed and low load conditions.