Numerical Investigation on the Mechanism of Tumble Caused Cycle-to-Cycle Variation of High-Tumble Spark-Ignition Engine

Due to increasingly strict emission regulations, improving and optimizing the combustion process is one of the main research focuses of internal combustion engine development. Combustion instability is a significant parameter, which affects the emission level, and it is reflected by cycle-to-cycle variation. Therefore, understanding the reasons for cycle-to-cycle variation is crucial for the internal combustion design. This paper investigates the causes of cycle-to-cycle variation of a spark-ignition engine through the 3D large eddy simulations done by CONVERGE v3.0. The analysis focuses on the mechanism and consequences of intake tumble flow variation. The variation of tumble ratio between cycles is found to cause fluctuation in turbulent kinetic energy, which will result in different combustion processes. Moreover, according to the results the tumble variation is attributed to the random turbulent eddies in a specific area between the cylinder head and inflow. Comparing tumble variations under different engine specifications, it is found that reducing the size of this area e.g., by changing cylinder head geometry or delaying intake valve opening, contributes to the smaller tumble variation.