部分负荷3500转/分工作状态下光学发动机缸内流动结构的多平面PIV分析

Within the framework of an investigation into valve operating strategies for homogeneous charge direct injection spark ignition engines under part load conditions this paper discusses the in-cylinder flow fields developed by running an optical engine with an early inlet valve closing strategy with a lift of 3.9 mm that produces 3bar IMEP at 3500 rpm under firing conditions. The experimental facilities are similar to previous work but measurement technique has been optimized with the significant aspect of this work being that the flow fields were determined in three vertical planes and one horizontal plane to highlight the three dimensional and the highly cyclic nature of the flow. These characteristics have significant impact on the application of the PIV technique and data processing to ensure a high degree of confidence in the flow fields generated. The time varying nature of this three dimensional flow field is discussed and how it impacts on the PIV measurement technique particularly as regards data acquisition and data processing. The true extent of the complex three dimensional flow field is readily seen and that, even though the combustion chamber geometry is symmetrical, the swirl flow field is not. The main features of the vertical flow structure are described over a crankangle period from 90oCA to 120oCA which highlight the dominant feature as being a wall jet flow which interacts with the piston crown to generate a strong reverse tumble flow.