Characterization of the effect of intake air swirl motion on time-resolved in-cylinder flow field using quadruple proper orthogonal decomposition

Abstract

a b s t r a c tThe control of intake air swirl motion is often used in spark-ignition direct-injection (SIDI) engine to improve its in-cylinder fuel-air mixing process especially under engine idle and low load conditions. In this experimental investigation, a novel technique combining the time-resolved particle image velocimetry (PIV) with quadruple proper orthogonal decomposition (POD) is implemented to analyze the time-resolved in-cylinder velocity measurements in an optically-accessible SIDI engine. The intake air swirl motion is introduced into the engine cylinder by a control valve installed in one of two air intake ports. Experimental results show that a strong linear correlation exists between the intake flow swirl ratio and vorticity flow field in the cylinder. This correlation ensures high data reliability of swirl motion control and provides a novel basis to directly compare the flow field measurements under different swirl ratio conditions. The quadruple proper orthogonal decomposition analysis is then applied to the velocity flow fields to separate the highly dynamic in-cylinder flow characteristics into four distinct categories: (1) dominant flow structure; (2) coherent structure; (3) turbulent structure; and (4) noise structure. The results show that the dominant flow structure varies strongly with swirl ratio, and its kinetic energy is also directly related to the swirl ratio. The coherent structure captures the large scale flow characteristics, but its kinetic energy is much lower and exhibits larger cycle-to-cycle variations. The turbulent structure contains similar level of kinetic energy at different swirl ratios but without much cycle-to-cycle variation. Finally, the noise structure contains very low kinetic energy which only alters the dynamic nature of the flow field slightly. In summary, the effect of swirl ratio on in-cylinder flow field is mostly captured by the dominant flow structure and partially captured by the coherent flow structure. The turbulent flow structure can characterize the high-order flow variation. The noise structure can be neglected due to the low energy captured.

LES‐VOF Simulation and POD Analysis of the Gas‐Jet Wiping Process in Continuous Galvanizing Lines

“…POD was originally introduced by Lumely et al for the analysis of turbulent flows . Various modifications and related methods exist . POD has been successfully applied in fluid mechanics to identify coherent dynamic flow structures of PIV, LES, or detached eddy simulation data .…”

“…Various modifications and related methods exist . POD has been successfully applied in fluid mechanics to identify coherent dynamic flow structures of PIV, LES, or detached eddy simulation data . Technological applications comprise the comparison of in‐cylinder flows of combustion engines, high speed trains, and airfoils .…”

On the Application of Proper Orthogonal Decomposition (POD) for In-Cylinder Flow Analysis

“…Therefore, in the recent years, the proper orthogonal decomposition analytical technique introduced firstly by Lumley [10] to the turbulence research community is considered as a powerful method to extract the most energetic structures in turbulent flows. The applications of POD have seen an increase in engine flow studies, in-cylinder flow analysis [4,11,12] cycle to cycle variations [13][14][15][16][17][18], variation of fuel spray structure [19,20] and combustion instability and misfire [14,21]. The aforementioned studies mainly have been concentrated on the evaluation of cycle-to-cycle variability in engines, either for air flow or for spray flow using POD.…”

Steady-State Experiment and Simulation of Intake Ports in a Four-Valve Direct Injection Diesel Engine

“…At present, the emissions have become the focus of attention, and the intake port is designed to introduce high levels of s "tumble" charge motion (Hartmann F et al, 2016), which can improve combustion. And the intake air swirl motion was very important to spark-ignition direct-injection engine (Choi, M et al, 2016), but also to the CNG direct injection engine (Zhuang, H et al,2016). So with the diesel engine combustion imposes stringent requirements on incylinder mixture formation and flow, well organized air flow in the cylinder is important for enhancing fuel-gas mixing rate and promoting burning rate in the combustion process.…”