Calculation of Flow in the Piston-Cylinder-Ring Crevices of a Homogeneous-Charge Engine and Comparison with Experiment

A crevice-flow model that had been published in the literature was reconstructed and used to calculate flow in the crevices between the piston, the cylinder, and the rings in a homogeneous-charge engine. The code was then modified to run interactively with a more sophisticated ring-friction model developed previously for calculation of the film thickness of lubricating oil on the cylinder liner.

The accuracy of this crevice-flow model was evaluated with engine-blowby data taken from tests on a multicylinder engine. The data covered wide ranges of speed (1300-3200 r/min) and load (260-780 kPa IMEP). It was concluded from this evaluation that the calculated magnitude of the blowby can differ from the measurement by more than 50% for the worst case. The measured trends, however, were correctly replicated with variations in both speed and IMEP, except at the highest speed of 3200 r/min. At 3200 r/min, the normalized blowby value was incorrectly calculated to increase due to fluttering of the second ring during the compression and expansion strokes. Furthermore, the calculations showed less sensitivity to speed variation than the measurements. The discrepancies between the calculation and the data appeared to be due to uncertainty in both wall temperature and discharge coefficients of the flow passages between the rings, which the program required as inputs.