Question 10 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is B *** ### 1. Explanation for why Option B is correct **B) This is a pushrod operated overhead valve engine with dry cylinder liners.** This statement is correct because the engine types commonly utilized as auxiliary power units (generator sets, pump drives) in smaller commercial vessels like tugs typically employ robust, time-tested designs. * **Valve Operating Gear (Pushrod/OHV):** Many reliable, medium-duty industrial and marine diesel engines (such as those from Caterpillar, Cummins, etc., often used for auxiliary power) utilize a **pushrod-operated overhead valve (OHV)** system. This system is known for its durability, relative simplicity, and ease of maintenance compared to complex overhead cam (OHC) systems. The illustration referenced (MO-0165, which typically shows a common industrial engine structure) would likely reveal the configuration that necessitates pushrods to actuate the valves from a cam located lower in the block. * **Cylinder Liner Type (Dry Liners):** **Dry cylinder liners** are pressed directly into the engine block and do not come into direct contact with the cooling water (the water flows through the jacket cast into the block around the liner). This design is common in many medium-horsepower, high-speed marine diesels because it simplifies the block casting, eliminates the need for complex sealing rings (which are required for wet liners), and provides adequate heat transfer for these applications. *** ### 2. Explanation for why the other options are incorrect **A) This is an overhead cam engine with wet cylinder liners.** * **Incorrect Valve Gear:** While OHC engines exist, they are less common in general auxiliary power applications than pushrod OHV engines, as OHC adds complexity and component count. * **Incorrect Liner Combination (for this engine class):** Wet liners are often associated with larger bore engines or those specifically designed for extremely heavy-duty, long-service life cycles (like large main propulsion diesels). This combination is unlikely for a standard tug auxiliary unit. **C) This is an overhead cam engine with dry cylinder liners.** * **Incorrect Valve Gear:** This fails for the same reason as Option A—the engine type commonly shown in marine auxiliary illustrations utilizes the simpler pushrod/OHV design rather than OHC. **D) This is a pushrod operated overhead valve engine with wet cylinder liners.** * **Incorrect Liner Type:** While the valve gear (Pushrod/OHV) is correct and common, the liner type specified is generally incorrect for the specific class of auxiliary engine targeted by this illustration. Engines that use **wet liners** require sealing rings (O-rings) to prevent cooling water leakage into the sump or combustion chamber. Although pushrod engines can certainly use wet liners, the specific design depicted in MO-0165 is characterized by the use of **dry liners**.