Investigation of In-Cylinder Cycle-to-Cycle Variation Using PIV, LIF and RANS Simulation

Cycle-to-cycle variation (CCV) of combustion is an issue that inevitably arises in internal combustion engines. There is a need to clarify and improve the situation, as well as predict it using computational fluid dynamics (CFD). This study involved carrying out experimental analyses of the factors that cause combustion cycle fluctuations, as well as predicting the CCV of gas flow using RANS. To elucidate the CCV in gas flow and combustion within gasoline engine, simultaneous TR-PIV, PLIF and direct-photography of flame propagation were performed using an optical single-cylinder engine, CCV prediction model for gas flow using RANS was verified. The results revealed the following: The variation in the equivalence ratio per cycle has little effect on initial combustion but does influence IMEP. Evaluating the laminar flame speed, S_L and turbulent flame speed, S_T as factors determining initial combustion revealed almost no correlation with S_L, while moderate correlations were observed between S_T and CA10. The position of the tumble vortex center at ignition timing was found to be critical; the vortex center position most favorable for advancing combustion timing was located to diagonally below the spark plug. The angular velocity at the center of the tumble vortex in the ensemble averaged flow significantly affected the turbulence kinetic energy (TKE) at the ignition timing, initial flame propagation speed, and CA10 phase. A model predicting cycle fluctuations during non-combustion was developed and verified against experiments. The CCV predicted using the spatial-based model reproduced the experimental CCV trends.