In this study, in-cylinder flow has been measured using high speed PIV to investigate turbulent characteristics of in-cylinder flow and to give a guiding principle for optimization of intake port and combustion chamber for down sized boosted engine. To clarify turbulence characteristics which will affect combustion process in engines, decomposition method of turbulence component from instantaneous velocity are investigated. Since velocity spectrum in 1 cycle from intake to compression stroke has a specific frequency where slope of the spectrum changes, a time filtering method for turbulence decomposition is proposed using this specific frequency as a cutoff. A characteristic of turbulent kinetic energy extracted by the proposed method well represents the expected flow characteristics at each test condition and shows good correlation with combustion characteristics such as burning speed and geometry of flame front. The obtain results show that turbulent intensity is high at a vortex center of tumble flow, which suggests that a control of tumble flow was very important in design of a boosted engine.

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