Cycle-Resolved LDV Measurements In a Motored Diesel Engine and Comparison with K-ε Model Predictions

Cycle-resolved LDV measurements of tangential mean velocities and turbulence intensities were made in a motored, single cylinder, Cummins NH diesel engine at 300 and 600 rpm. The measurements were made at eight locations in a plane 0.9 cm below the cylinder head. The combustion chamber and intake configuration of this low-swirl, low-squish engine were nearly identical to the stock configuration. For improved optical access, however, the compression ratio was lower in the test engine (10:1) than in the production engine (14.5:1). The measured turbulence intensities were compared to values computed with KIVA, an in-cylinder fluid dynamics flow code with a k-ε turbulence model.

The measurements show that the mean velocity field is three-dimensional before TDC, consisting of both a weak swirling motion and a weak tumbling motion. After TDC the tumbling motion subsides and only the swirling flow is apparent. The TDC turbulence intensity (cycle-resolved) has a very low value of l/6th the mean piston speed. The 3-D nature of the mean flow Field prior to TDC could not be predicted, because limitations in the flow code and computer resources allowed only 2-D calculations to be performed. Although the computed and the measured mean velocities before TDC differed, the computed turbulence intensities agreed closely. The agreement was particularly good (within 10%) after TDC, when the tumbling motion was no longer present and the flow became nearly two-dimensional.