Stereoscopic Micro-PIV Measurement of Near-Wall Velocity Distribution in Strong Tumble Flow under Motored SI Engine Condition

2020-01-2019

09/15/2020

Features
Event
SAE Powertrains, Fuels & Lubricants Meeting
Authors Abstract
Content
In a state-of-the-art lean-burn spark ignition engine, a strong in-cylinder flow field with enhanced turbulence intensity is formed, and understanding the wall heat transfer mechanism of such a complex flow is required. The flow velocity and temperature profiles inside the wall boundary layer are strongly related to the heat transfer mechanism. In this study, two-dimensional three-component (2D3C) velocity distribution near the piston top surface was measured during the compression stroke in a strong tumble flow using a rapid compression and expansion machine (RCEM) and a stereoscopic micro-PIV system. The bore, stroke, compression ratio, and compression time were 75 mm, 128 mm, 15, and 30 ms (equivalent to 1000 rpm), respectively. A double-pulse Nd:YAG laser sheet was introduced from the intake side, and PIV images were captured near the piston surface around the TDC under motored conditions with a measurement region of 5.2 mm × 6.9 mm (1200 × 1600 pixel, 4.3 μm/pixel) using two CCD cameras. The 2D3C velocity fields show that the magnitude of the wall-tangential velocity (u) is generally larger than the wall-normal velocity (v) and comparable to the tumble axial (laser sheet-normal) velocity (w). As the measured time approaches TDC, u and v tend to decay, while w does not decay compared to u. As a result, the w component contributes more to the 3D vector magnitude than u and v at the closest observation time to TDC. In addition, the main flow is in the piston horizontal direction, and the direction fluctuates in the tumble axial direction because the w direction fluctuates in each cycle. Moreover, separation of the large and small-scale velocity components using a spatial filter enables calculation of turbulent kinetic energy (TKE) at the region near the piston top surface. The contribution of v’, u’, and w’ to TKE increases in this order. Additionally, a large cycle-to-cycle variation of TKE was observed.
Meta TagsDetails
DOI
https://doi.org/10.4271/2020-01-2019
Pages
11
Citation
Yamakita, Y., Bae, J., Nagasawa, T., and Kosaka, H., "Stereoscopic Micro-PIV Measurement of Near-Wall Velocity Distribution in Strong Tumble Flow under Motored SI Engine Condition," SAE Technical Paper 2020-01-2019, 2020, https://doi.org/10.4271/2020-01-2019.
Additional Details
Publisher
Published
Sep 15, 2020
Product Code
2020-01-2019
Content Type
Technical Paper
Language
English