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Determining locations at which knocking events appear frequently is a very important tool for optimizing the efficiency of S.I.-Engines. The knock behavior of two Direct-Injection Engines (one with wall guided fuel delivery - Mitsubishi GDI-engine - and a single-cylinder test engine with narrow arrangement of spark plug and injector) was tested and the location of appearing knocking was detected by the use of optical fiber technique. The optical investigations were conducted using a spark plug equipped with 8 optical sensors evenly distributed in a ring on the ground electrode of the standard spark plug. The intensity of flame radiation in the observing area of the optical sensors were measured. As knocking combustion produces pressure waves exciting gas oscillations, each compression of residual exhaust gas causes a steep increase of the measured flame intensity curve.