City Research Online

Abstract

The measurement of wall shear-stress along the crown of a moving piston is accomplished with an array of hair-like, flexible micro-pillar sensors (MPS) in an internal combustion (IC) engine during intake flow conditions. The MPS are wall-clamped flexible micro-cylinders of 20micron diameter made of polydimethylsiloxane (PDMS) positioned on the surface of a transparent planar piston crown and protruding into the boundary layer flow above the piston at a height of 390micron. Their tips are labelled with fluorophores and are illuminated with a scanning laser-sheet system that follows the piston motion in synchronous manner. The flow-induced deflection is recorded through the transparent piston crown from below with a compact shaft-mounted high-speed camera recording the fluorescent re-emitted light from the pillar tips and using the fact of optical wave-guide features of the transparent micro-pillars. The experiments were performed in a transparent 4-valve engine setup (1.6 liter Prince 2, N13B16) during the intake phase. In order to improve the temporal resolution, the running speed of the engine was scaled down using water as working liquid. A static and dynamic sensor-calibration enabled the precise measurements of the wall-shear stress distribution with the sensor array. Due to spatial resolution limits of current available compact high-speed camera the recorded region along the piston was limited to 4x2 mm2 with 8x4 pillars in full view. The recordings at 300fps show the WSS fluctuations induced by the valve-jet / piston-wall interaction in the beginning of the intake with strong wall-normal motion forming critical points in the WSS field such as saddles, nodes and foci. Over the intake cycle > CA 80° these fluctuations die out and flow is transformed into wall-parallel coherent motion prescribed by the formation of the tumble.

Publication Type:	Conference or Workshop Item (Paper)
Publisher Keywords:	IC engine flow, micro-pillar imaging, wall-shear stress, fluorescent labelled, optical wave guide
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering

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