Large eddy simulation of in-cylinder turbulent flows in a DISI gasoline engine

A large eddy simulation (LES) approach is used to study the in-cylinder turbulent flows of a direct injection gasoline engine, with emphasis on the relationship between the in-cycle turbulent fluctuations and the inter-cycle, i.e. cycle-to-cycle variation (CCV). In total 13 continuous cycles have been calculated, both the single cycle result and phase-averaged result have been compared with our PIV measurements, and reasonable agreements are obtained. Computational results show that, the in-cylinder turbulence is induced primarily by the intake jet. At the early stage of the intake stroke, both the turbulent fluctuations and cyclic variations are intensive and they are of the same magnitude order. While in the compression stroke, the decay of turbulent fluctuations are greater than that of the cyclic variations, and the ratio between them is less than 15%, and the flow field tends to be isotropic. This study demonstrated that LES is capable to describe more realistically details and rules of the in-cylinder turbulent flow and the cycle-to-cycle variations. By using LES coupled with the Q-criterion, the large scale coherent structures in the turbulent flow field can be identified.