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We visualized behavior of crevice flows in a spark ignition gas engine by laser-induced fluorescence (LIF) of acetone and OH. The fuel used in this work was methane with 10 vol. % acetone vapor. Acetone acts as a LIF tracer for unburned fuel, and OH radical which exists naturally in hydrocarbon flames is used as a marker species of high temperature zones. This technique enables simultaneous tomographic observations of high temperature zones and unburned zones in engine cylinders, and the technique gives abundant information on oxidation process of fuel. A transparent engine whose cylinder wall was made of fused silica for observations and laser access was used for experiments. A crevice flow released from a crevice between a piston and a cylinder wall was visualized. In this work, we investigated effects of valve timing, back-pressure, and ignition timing. We found that behavior of the crevice flow changes suddenly at moment of exhaust valve opening.