Analysis of Cycle-to-Cycle Variation in In-Cylinder Flow and Combustion by Using Simultaneous PIV Measurements on Two Sections

To realize stable combustion in lean or diluted conditions, reducing cycle-to-cycle variations of flow and fuel distribution is important. In this study, the effect of initial flow field was examined by simultaneous Time-Resolved PIV and visualization on two cross-sections in a fully optical-access engine under motoring and firing conditions with homogeneous pre-mixture. As a result, Omega index was defined and plotted on the correlation map between turbulence kinetic energy and CA10 (duration from ignition timing to 10% to the total accumulated heat). The omega index describes the strength of a horizontal flow field that resembles the shape of the Greek letter Omega. The plots with high Omega index were found frequently in the CA10 retarded cycles. On the other hand, the plots with low Omega index have simple tumble flows and the correlation was clearly found. This means that not only turbulence but also mean velocity’s pattern are important for the estimation parameter of cycle-to-cycle variation. As a result, it was found that the initial tumble should be given as “outside-fast” and then, a nearly homogeneous tumble was formed near spark timing without an Omega flow.