Browse Publications Technical Papers 2019-01-0006
2019-01-15

LES analysis on cycle-to-cycle variation of combustion process in a DISI engine 2019-01-0006

Combustion cycle-to-cycle variation (CCV) of Spark-Ignition (SI) engines can be influenced by the cyclic variations in charge motion, trapped mass and mixture composition inside the cylinder. An extremely high CCV leads to misfire or knock, limiting the engine’s operating regime. In the present study, numerical simulations were used to study the combustion CCV in a single cylinder Direct Injection Spark-Ignition (DISI) engine. To explore the mechanism of the effect of flow field and mixture compositions on the intensity of CCV, two fired operating conditions (one stable condition without external EGR and one unstable condition with 15% external EGR) were simulated. A large eddy simulation (LES) approach was developed to capture the CCV by accurately resolving the turbulent flow field spatially and temporally. The G-equation combustion model was adopted to track the turbulent flame propagation. Further, the ignition process was modeled by sourcing energy during the breakdown and arc phases. Detailed chemistry was solved both inside and outside the flame front. A compact 48-species 152-reactions primary reference fuel (PRF) reduced mechanism was employed to balance the accuracy of accounting for the chemistry and computational cost. A good agreement with the available experimental data was achieved and the simulations showed the ability to predict the trend in CCV intensity with changing operating conditions. Based on the results, the effect of early flame development on the combustion process was analyzed. Furthermore, correlation analysis between early flame development (speed and topology) and pressure-related and burn-related parameters were conducted under the two different operating conditions.

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