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The lubrication mechanism is discussed by measuring the oil film behavior. The oil film behavior is evaluated by the oil film thickness and oil film velocity map. The combination method of laser induced fluorescence method (LIF) and particle image velocimetry (PIV) is applied to measure the oil film behavior. The oil film thickness is measured by LIF and its velocity distributions are measured by PIV. The combination method can provide both of the film thickness and velocities simultaneously. The first trial is performed in the model engine for checking the dynamics measurement of the oil film thickness by the LIF. The results show a difference of the oil film thickness distribution with crank angle. The combination method is tested in the engine with 4-cycle and 2-cylinder optical access engine with motoring condition. One cylinder of the engine is sapphire cylinder for observing oil film behavior on the piston skirt. Two clearances of the piston skirt of 30 µm and 100 µm is tested.

The combination method for measuring the oil film thickness and velocity is proposed. The oil film thickness is measured by laser induced fluorescence (LIF) method and its velocity is measured by particle image velocimetry (PIV). A model engine is employed in order to check the LIF measurement for oil film thickness, and an optical access engine based on production engine is utilized for both measurements of oil film thickness and velocity. In the combination method, LIF images are used in the PIV measurement instead of particle images. From the results, the oil film thickness and velocity can be measured simultaneously by the combination method utilizing only LIF dye. The oil film thickness and velocity are presented along with crank angle of the engine under the motoring operation. The oil film velocity is also measured under the firing operation.