Question 29 MODE02 - Assistant MODU Engineer

The Correct Answer is A ### 2. Why option A ("Wet-type cylinder liners") is correct: Wet-type cylinder liners are the component most susceptible to cavitation corrosion/erosion due to their direct mechanical interaction with the moving piston assembly. * **Mechanism of Vibration:** During engine operation, the piston movement, particularly the change of direction at the top and bottom dead centers and the lateral forces exerted during the power stroke (known as "piston slap"), causes the thin wall of the wet liner to vibrate rapidly and violently (high frequency, low amplitude). * **Inducing Cavitation:** This intense vibration of the liner wall transmits kinetic energy into the adjacent cooling water, creating momentary, localized low-pressure zones. In these zones, the coolant flashes into vapor bubbles (cavities). * **Erosion:** As the vibration cycle continues, the local pressure rapidly increases, causing these vapor bubbles to violently implode (collapse) directly against the liner's outer surface. This implosion generates powerful shockwaves and micro-jets that physically hammer and erode the metal, leading to the characteristic pitting associated with cavitation corrosion/erosion. ### 3. Why the other options are incorrect: **B) Cylinder cooling water jackets:** The water jackets (the main block casting surrounding the liners) are structurally massive and rigid. They do not experience the high-frequency vibration or wall movement transmitted by the piston slap that is necessary to induce cavitation in the immediately adjacent coolant. **C) Cylinder head cooling water passages:** The cylinder head passages are subjected to high thermal stress and flow turbulence, which might cause flow-induced cavitation (usually near constrictions or sharp turns), but they lack the intense, direct mechanical vibration source (piston slap) that specifically targets the surfaces of the wet liners. **D) Engine exhaust cooling water jackets:** These jackets manage high heat but are primarily static structural components. They are generally susceptible to standard corrosion or scaling (due to high temperatures and poor flow), but they are not subject to the rapid, mechanical vibration forces required to generate cavitation erosion like the cylinder liners are.