Time-Resolved stereoscopic PIV measurements of cyclic variations in an internal combustion engine

Time-Resolved stereoscopic PIV measurements of cyclic variations in an internal combustion engine

Karhoff, D.C.
Bücker, I.
Klaas, M.
Schröder, W.

2013-07-02

The flow field during the intake and the compression stroke of an optical four-stroke, four-valve, single-cylinder gasoline type demonstrator engine is measured using time-resolved stereoscopic particle-image velocimetry (PIV) to analyze these flow structures. The flow is measured in the tumble plane at an engine speed of 1500 rpm in 50 consecutive cycles to account for cycle-to-cycle variations. The sampling rate is set to 3.2 kHz such that one pair of double-images is recorded at every 2.8° crank angle. Using the velocity components derived from the PIV measurements, the main vortical structure is visualized, i.e., the main tumble vortex in the symmetry plane between the inlet and outlet valves, and the temporal development of the turbulent kinetic energy is determined. The results show high turbulent kinetic energy during the intake stroke which decreases at increasing crank angles and remains at an almost stable level during the compression stroke. At the end of compression, the vortices break up and the turbulent kinetic energy dissipates. The ensemble averaged mean kinetic energy shows that the very well conserved tumble vortex dominates the flow field during intake and compression and exhibits the typical tumble spin-up towards the end of compression, followed by a tumble break up. A proper orthogonal decomposition of the flow field shows that the tumble vortex forms at early crank angles and dominates the flow regime, stabilizing during the compression stroke. With the beginning of the tumble breakdown, the first POD mode drops rapidly, indicating an energy transfer to higher modes. The analysis of cyclic variations reveals significant discrepancies in the temporal development of the turbulent kinetic energy in the symmetry plane when comparing individual cycles with each other. The same applies to the path of the tumble core in the symmetry plane.

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Conference proceedings

conference paper

(c) 2013 Karhoff, D.C.; Bücker, I.; Klaas, M.; Schröder, W.