Question 38 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is A. **Explanation for Option A (Wet-type cylinder liners):** Wet-type cylinder liners are correct because they are subject to very high-frequency, low-amplitude vibration during engine operation. This vibration is caused by the movement of the piston, combustion forces, and the resulting mechanical stress. When the liner vibrates, it creates alternating areas of low and high pressure in the surrounding coolant (the cooling water jacket). If the local pressure drops below the vapor pressure of the coolant, bubbles (cavities) form instantly. As the liner moves back, the local pressure increases, causing these bubbles to violently collapse (implode) on the surface of the liner. This repeated, intense micro-jetting impact physically removes the protective oxide layer and erodes the metal surface, leading directly to cavitation corrosion/erosion pitting. Because the liner is a relatively thin component separating the combustion heat from the coolant, it is the most vibratory component exposed to the coolant, making it the primary site for cavitation damage. **Why the other options are incorrect:** * **B) Cylinder head cooling water passages:** While cylinder heads are exposed to high thermal stress and some flow turbulence, the bulk material is generally thicker and less prone to the rapid, high-frequency mechanical vibration that causes cavitation on the magnitude seen on thin wet liners. Damage here is more commonly associated with thermal fatigue or general erosion from high flow velocity rather than vibration-induced cavitation. * **C) Cylinder cooling water jackets:** This option refers to the stationary block casting surrounding the liner (the outer wall of the jacket). This structure is rigid and does not vibrate with the frequency or amplitude required to induce significant localized cavitation damage on its own surfaces. It contains the liner, which is the vibrating component. * **D) Engine exhaust cooling water jackets:** These jackets cool the exhaust manifolds. While they manage high heat, they are structurally rigid and are not subjected to the direct, cyclic combustion forces transmitted through the piston/liner assembly. Any damage here is typically due to general corrosion or scaling related to low flow or high temperature, not vibration-induced cavitation.