Daming Liu

Analysis of In-Cylinder Turbulent Flows in a DISI Gasoline Engine With a Proper Orthogonal Decomposition Quadruple Decomposition

The proper orthogonal decomposition (POD) method is applied to analyze the particle image velocimetry (PIV) measurement data and large eddy simulation (LES) result from an in-cylinder turbulence flow field in a four-valve direct injection spark ignition (DISI) engine. The instantaneous flow fields are decomposed into four parts, namely, mean field, coherent field, transition field and turbulent field, respectively, by the POD quadruple decomposition. The filtering method for separating the four flow parts is based on examining the relevance and correlations between different flow fields reconstructed with various POD mode numbers, and the corresponding reconstructed fields have been verified by their statistical properties. Then, the in-cylinder flow evolution and cycle-to-cycle variations (CCV) are studied separately upon the four field parts. Results indicate that each one of the four field parts exhibits its own flow characteristics and has close connection with others. Furthermore, the mean part contains the most kinetic energy of the entire flow field and represents the bulk flow of the original in-cylinder velocity field; the CCV in this part could almost be neglected, while the coherent field part contains larger scale structures and the most fluctuating energy, and possesses the highest CCV level among the four parts.

Insights into the development of the tumble motion using the direct and indirect steady-flow test methods

The measurement and evaluation of the tumble motion in an engine cylinder are widely achieved by steady-flow tests. However, there is absence of a standard methodology for the evaluation of the tumble motion in the steady-flow tests. The aim of this paper is to analyse the variation in the evolution of the tumble motion with different tumble test methods. Both steady-flow tests and particle image velocimetry measurements were carried out on a commercial four-valve spark ignition engine. The results showed that, for the indirect test method, the variation in the diameter of the cross pipe has a negligible effect on the non-dimensional tumble intensity, although the angular momentum flux is proportional to the diameter of the cross pipe owing to the conservation of the rotational kinetic energy flux. For the direct test method, there is an obviously abrupt rise in the tumble intensity with increasing valve lift because the in-cylinder flow evolves into a single large-scale tumble vortex in a short transition phase. Moreover, the rotational speed of the tumble flow increases when a dummy cylinder with a smaller outlet diameter is used in the direct test method.