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A coupled phase-invariant POD and DMD analysis for the characterization of in-cylinder cycle-to-cycle flow variations under different swirl conditions

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Abstract

The cycle-to-cycle variations (CCV) of in-cylinder flow make critical impact on internal combustion engine performance. The flow structure evolution and its cyclic variations need to be fully understood. In this study, a novel approach which couples proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) is proposed to identify the CCV features of in-cylinder flow under various swirl conditions. The methodology is applied to a time-resolved high-speed particle image velocimetry (PIV) dataset which measures the crank angle resolved flow field on a swirl plane 30 mm below the injector tip in the cylinder. Phase-invariant POD and DMD analyses are conducted on 121 phase angles which cover the majority of in-cylinder flow evolution stroke from -300 crank angle degree (CAD) after top dead center (TDC) to -60 CAD after TDC with a 2-CAD resolution. The modal decomposition analyses are applied on 100 engine cycles individually to investigate the cyclic variation. Phase-invariant POD identifies the steady structure and coherent structure of the in-cycle engine flow evolution features. A novel stepwise traversal correlation search method (STCSM) is proposed to connect the DMD modes with POD decomposed coherent structure. This analysis approach is capable of identifying the characteristic frequencies and correlating them with the dynamical decay rates of underlying flow coherent structures with regards to CCV. In summary, the CCV of dynamical features for all swirl ratio conditions show similar variation level at intake stroke. Inducing a higher swirl ratio can minimize the effect of intake flow dynamics and suppress the cyclic variability of engine flow at compression stroke.

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Acknowledgements

The experiments were carried out at the National Engineering Laboratory for Automotive Electronic Control Technology of the Shanghai Jiao Tong University. The authors gratefully appreciate the experimental support by Prof. Min Xu and Prof. Xuesong Li of Shanghai Jiao Tong University.

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Correspondence to David L. S. Hung.

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Liu, M., Zhao, F. & Hung, D.L.S. A coupled phase-invariant POD and DMD analysis for the characterization of in-cylinder cycle-to-cycle flow variations under different swirl conditions. Flow Turbulence Combust 110, 31–57 (2023). https://doi.org/10.1007/s10494-022-00348-4

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  • DOI: https://doi.org/10.1007/s10494-022-00348-4

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