Analysis of In-Cylinder Flow for Hybrid Gasoline Engine using High-Speed Particle Image Velocimetry

To curb global warming, reduction of CO2 emissions in automotive powertrains is required. Hybridization and further improvement of thermal efficiency has been promoted in internal combustion engines. Therefore, the 2.0-liter inline 4-cylinder direct-injection engine for 2 motor-hybrid powertrain have been developed to realize rapid combustion by in-cylinder flow enhancement. In this paper, in-cylinder flow analysis using high-speed PIV on the optical single-cylinder engine was performed, and evaluated the combustion promotion concept by analyzing the bulk flow and the turbulence. To achieve rapid combustion, the intake port shape for tumble flow enhancement and bowl-in type piston which was smoothly converted the tumble flow to upward flow were examined. As a method for turbulent component decomposition, the time filter method proposed by the authors were applied. The characteristics of the time filter method is that turbulent component does not include the cycle-by-cycle fluctuations of mean flow component (low-frequency component), which is considered to not contribute to combustion promotion. As result, compared to the initial development specification, it was confirmed that the velocity of intake flow toward to the exhaust side of the in-cylinder flow enhancement specification increased, and the velocity of downward flow to descend the exhaust side increased. In addition, it was confirmed that the downward flow at exhaust side was smoothly converted into the upstream flow by the piston top. Analysis of the turbulent component obtained by the time filter method showed that the turbulent kinetic energy of the in-cylinder flow enhancement specification increased about 20% at the latter half of compression stroke. And the combustion duration decreased by about 4 deg. on the metal engine. Thus，it was clarified that the combustion promotion concept was realized by in-cylinder flow enhancement.