Abstract
The erosion at cylinder liners or cylinder blocks in water cooled diesel engines is considered to be due to the collapse of cavitation bubbles attributed to the cylinder liner vibration.In this study, using a model equipment and an actual engine, the behavior of cavitation bubbles grown in a water jacket is observed continuously under the several liner vibration conditions by taking direct microscopic photographs with high speed drum camera. In case that the vibration velocity of the cylinder liner is small, gaseous cavitation bubbles caused by dissolved air or contaminated air are generated. These gaseous bubbles stay for a long time more or less independent of transient change in the water pressure fluctuation. And the cooling water pressure fluctuation is assessed from the vibration velocity of the cylinder liner employing a water hammer equation. As the liner vibration velocity is increased, vaporous cavitation bubbles are generated because the cooling water pressure fluctuation reaches to the water vapor pressure. And the critical vibration velocity of the cylinder liner is revealed in term of generation of these vaporous bubbles. These vaporous cavitation bubbles are initiated as small bubbles, grow up to about 200-300μm in diameter, and a shock wave is took place in the instant of bubble collapsing after the life time about 150μs.
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