1997-10-01

Turbulent Flow Field Characteristics in a Motored Reciprocating Engine 972833

Coincident 3-d velocity measurements in the flat combustion chamber of a motored single cylinder engine have been performed using Laser-Doppler-Velocimetry. The 3-d LDV System consisted of three beampairs (514nm, 488nm and 476.5nm) and two fiberoptic probes operated in 90° cross-scatter mode obtaining high spatial and temporal resolution as well as high signal quality. Burst Spectrum Analyzers have been thereby used for signal processing.
The time histories of the three velocity components have been acquired for moderate engine speeds (600, 1000 and 1500RPM). The swirling motion in the cylinder was also varied by choosing different fixed positions of a shrouded intake valve relative to the intake port. Several measuring locations in the combustion chamber have been studied in order to investigate homogeneity.
Mean velocities and fluctuation intensities of the turbulent field were evaluated using ensemble averaging. In addition evaluation of the Reynolds shear stress tensor components have been made for the investigated locations and engine operating conditions. The integral time scales of the flow field were computed aa well as the associated integral length scales using the Taylor Hypothesis. Isotropy of the turbulence field was also investigated.
Strong dependence of all quantities on measurement location and on intake shrouded valve position have been observed while scaling with engine speed is in reasonable agreement with dimensional arguments. In this way deeper insight into structural features of the flow during compression and expansion has been obtained.

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