CASE STUDY USING PISDYN OF THE EFFECT ON ... - Ricardo

the PISDYN model would be able to satisfactorily predict the wear patterns on subsequent
design iterations of the piston. Consequently, only two prototype versions of the piston needed to
be actually produced and tested - an initial design and the final design.
Two separate simulations of each design were performed at maximum power operating
conditions. In simulation A, where roughness parameters of the skirt and liner were set in
PISDYN to replicate actual values, the purpose was to determine the skirt-liner friction and to
determine the maximum wear loads in order to ascertain whether scuffing could occur. In
simulation B, the roughness parameters were altered such that the simulation would better
predict the wear pattern on the piston. It was necessary to make special adjustments to predict the
wear pattern in order to account for the fact that during actual use the wear pattern will be wider
than predicted. This is because in actual use, the region of the skirt most prone to wear will be
first to experience a reduction in thickness (and therefore an increase in clearance with the liner),
leading to surrounding regions of the skirt beginning to wear against the bore. In both
simulations, worst case conditions were assumed by setting skirt-bore clearance to the minimum
of the tolerance range.
Simulation A of the final design predicted that scuffing would not be a problem. This was
confirmed by a hot scuff engine test at maximum power output conditions. Simulation B of the
final design predicted that the wear pattern on the skirt was suitable. This was again confirmed
by the engine test. Figures 1 and 2 compare the wear patterns from the PISDYN simulation and
from the hot scuff engine test respectively. The two patterns are quite similar apart from a wear
region in the lower part of the skirt around the thrust plane, which was not predicted by the
simulation.
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