A Combined Numerical and Experimental Study of the 3D Tumble Structure and Piston Boundary Layer Development During the Intake Stroke of a Gasoline Engine

Abstract

Due to its positive effect on flame propagation in the case of a well-defined breakdown, the formation of a large-scale tumble motion is an important goal in engine development. Cycle-to-cycle variations (CCV) in the tumble position and strength however lead to a fluctuating tumble breakdown in space and time and therefore to combustion variations, indicated by CCV of the peak pressure. This work aims at a detailed investigation of the large-scale tumble motion and its interaction with the piston boundary layer during the intake stroke in a state-of-the-art gasoline engine. To allow the validation of the flow near the piston surface obtained by simulation, a new measurement technique called "Flying PIV" is applied. A detailed comparison between experimental and simulation results is carried out as well as an analysis of the obtained flow field. The large-scale tumble motion is investigated based on numerical data of multiple highly resolved intake strokes obtained using scale-resolving simulations. A method to detect the tumble center position within a 3D flow field, as an extension of previously developed 2D and 3D algorithms, is presented and applied. It is then used to investigate the phase-averaged tumble structure, its characteristics in terms of angular velocity and the CCV between the individual intake strokes. Finally, an analysis is presented of the piston boundary layer and how it is influenced by the tumble motion during the final phase of the intake stroke.

Investigation of an IC Engine Intake Flow Based on Highly Resolved LES and PIV

“…studies, it was shown that the valve shaft strongly influences the intake jet at the valve center plane [5,30]. The differences in hu c i no between different cases decrease to Y* % 1.5 and remain nearly constant afterwards.…”

“…Prism layers are used to obtain an improved resolution of the boundary layer in an attempt to place the first layer within the viscous sublayer (i.e. y + < 5) [1,5,39]. In addition, a medium mesh is investigated, which is not shown for the sake of brevity.…”

“…fuel-air mixing and flame propagation) is described in [1,2]. In several studies it was shown that the momentum introduced by the intake jet is the main contributor to the large-scale tumble [3][4][5]. Due to this strong dependency on the intake jet, the intake port is optimized intensively during the engine design process to obtain a distinctive tumble motion throughout the intake and compression stroke.…”

Theoretical calculation model of the propulsion engine admission parameters for different functional conditions

“…By taking into consideration the recommended values for on full load [2], and also experimental results [3], it was subsequently adopted a filling coefficient 0.87. Further, the situation of intake pressure variation was developed, at the same time with the engine load modification.…”

Numerical Prediction of Cyclic Variability in a Spark Ignition Engine Using a Parallel Large Eddy Simulation Approach

“…They showed that approximately 30% of the fluctuating kinetic energy was generated due to cyclic fluctuations in the chamber near TDC. There have been a few other experimental studies [7,8], which focused on the large-scale structures and their cyclic variability in SI engines. However, in experimental studies, it is difficult to isolate the different coupled processes and hence cannot be used to explain the causes of CCV.…”