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The present paper aims at investigating the flow field behavior within a reciprocating engine under motoring conditions. Simultaneous two velocity components of the air velocity were acquired at different engine speeds within the cylinder at different radii from the cylinder axis. Mean motion, integral time scales and Reynolds shear stresses, for the radial and tangential components, were estimated from the instantaneous velocity data by applying an ensemble averaging technique. The integral time scale was obtained from the single point time autocorrelation function whereas, the Reynolds shear stresses were computed through the estimate of the degree of the fluctuations correlation. Tests, carried out at 1,000, 1,500, and 2,000 rpm, showed that the tangential mean motion scales approximately with engine speed whereas a radial inward motion can be observed during the last part of compression.

Tangential component of velocity and turbulence were measured in three locations in the re-entrant combustion chamber of a motored single-cylinder d.i. Diesel engine (0.435 liter, 21:1 compression ratio) using a Laser Doppler Velocimetry system. Moreover, a modified LDV system with two-probe volume was used to measure directly lateral integral length scales of the velocity tangential component at two engine speeds. The measurements were made on a horizontal plane at 5 mm below the engine head from 100 degrees before TDC to 60 degrees after TDC of both the compression and expansion strokes. The engine was motored at 1,000 and 1,500 rpm respectively. An ensemble-averaging technique was performed to analyze the instantaneous velocity information supplied by two Burst Spectrum Analyzers. The lateral integral length scale was obtained from the integral of the spatial correlation coefficient of the velocity fluctuation for different separation.

In-cylinder measurements of turbulent integral length scales, carried out during the last 60 degrees of the compression stroke at 600 and 1,000 rpm by a two-probe volume LDV system, were used to assess the capability of the k-ε model used in KIVA-II code. The objective of the paper is to address the following question: what is the most reasonable definition of turbulent length scale in the k-ε model for engine applications? The answer derived from the comparison between KIVA predictions and experiments that showed a fair agreement between the computed turbulent length scale and the measured lateral integral length scale. The agreement is a result of proper choice of the initial swirl ratio and turbulent kinetic energy at inlet valve closure (IVC) by taking into account the LDV measurements and the value of the constant Cμε in the k-ε model equations that relates the turbulent length scale to k and ε.