Question 53 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B ### Explanation of Option B (Correct) **B) The cylinder liners are of the wet type and are replaceable inserts.** This statement is correct because it reflects the standard engineering practice for medium to large heavy-duty diesel engines, such as those used for marine auxiliary generator sets. 1. **Replaceable Inserts:** High-power diesel engines are designed for long service life and cost-effective maintenance. Making the liner a replaceable insert allows mechanics to swap out the worn cylinder wall (liner) during an overhaul without replacing the entire expensive cylinder block. 2. **Wet Type:** A wet liner is designed so that its outer wall is in direct contact with the engine coolant, forming the inner seal of the water jacket. This design provides highly effective and necessary heat transfer, which is crucial for controlling the high operating temperatures and thermal stresses inherent in continuous-duty, high-output marine generator engines. ### Explanation of Other Options (Incorrect) **A) The cylinder walls are integral (non-replaceable) to the cylinder block.** This design is limited to small, light-duty, or automotive-style engines. Heavy-duty marine engines are designed for multiple major overhauls; an integral cylinder wall would necessitate replacing the entire cylinder block when bore wear occurs, making maintenance prohibitively expensive and inefficient. **C) The cylinder liners are of the jacketed type and are replaceable inserts.** While the cylinder block *is* jacketed (contains cooling passages), "wet type" is the specific and correct term used in diesel engine technology to describe a liner that is in direct contact with the coolant. **D) The cylinder liners are of the dry type and are replaceable inserts.** A dry liner is a sleeve pressed into the block and does not directly contact the cooling water; the metal of the block separates the liner from the coolant. While replaceable, dry liners offer less effective heat transfer than wet liners. Due to the severe thermal demands of continuous-duty marine generator operation, the superior cooling capability of the **wet type** liner is usually required.