Troels Dyhr Pedersen.indd - Solid Mechanics

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Figure 10: Steel plate with pressure transducer
Figure 11: HCCI cylinder to the left, DI CI cylinder to the right
The engine construction is possibly one of the most important factors in determining the transfer of sound from
the combustion to the surroundings. Therefore the results obtained with this engine are of course not directly
applicable to any other engine. The effect of the various piston crowns on the in-cylinder pressure effects and
hence their noise reducing capabilities does however not depend on the engine surrounding it. The difference in
noise reducing capability as an effect of the piston crown geometry will therefore most likely apply to any
engine of similar size.
CREVICE VOLUMES
The volumes between piston and cylinder were of varying size in this experiment. This influences the
combustion efficiencies and hence the IMEP. Table 2 holds the calculated values of the crevice volumes. These
calculations are based on the piston crown measures at 25 °C. The actual volumes will decrease as the piston
crown heats up.
The crevice volumes of the piston crowns with 27 mm crevice height is very large because it was necessary to
increase the radial clearance to avoid contact with the steel plate, and because piston rings could not be used on
the crown since the gap between the steel plate and the cylinder liner did not allow for piston ring passage. If
the piston crowns were to be used in a normal engine the crevice volumes could be reduced to the same size as a
normal diesel piston.