Question 28 3AE01 - Third Assistant Engineer

The Correct Answer is C ### Explanation of Why Option C is Correct The question references a specific illustration (MO-0163, commonly associated with standardized marine engineering examinations and training materials) which typically depicts a common, modern marine medium-speed diesel generator drive engine, such as the MaK M32 or similar models. 1. **Operating Cycle (Four-Stroke):** Medium-speed engines used for marine generator drive applications (auxiliary engines) are predominantly of the **four-stroke cycle** design. This cycle is favored for its superior fuel efficiency, better low-load performance, and simpler scavenging/turbocharging arrangements compared to the two-stroke cycle used primarily for large, low-speed main propulsion engines. 2. **Cylinder Configuration (90° V-type):** The engines depicted in these educational materials, particularly in higher cylinder counts (e.g., V12, V16), utilize a **90° V-type** configuration. A 90-degree angle provides optimal primary and secondary balance when combined with a specific firing order, resulting in smoother operation, reduced vibration, and a more compact design suitable for auxiliary machinery spaces. Therefore, the engine is a four-stroke cycle engine with a 90° V-type configuration. ### Explanation of Why Other Options Are Incorrect **A) This is a two-stroke cycle, 60° V-type engine.** * **Incorrect Cycle:** Medium-speed auxiliary engines are typically four-stroke, not two-stroke. * **Incorrect Angle:** While 60° V-angles exist in some engine designs, 90° is standard for optimal balance in the specific type of marine generator engine illustrated. **B) This is a two-stroke cycle, 90° V-type engine.** * **Incorrect Cycle:** The four-stroke cycle is standard for this application (generator drive). Two-stroke engines are almost exclusively low-speed crosshead engines used for main propulsion. **D) This is a four-stroke cycle, 60° V-type engine.** * **Incorrect Angle:** The 90° V-angle is the standard configuration used in these high-output, V-type auxiliary generator engines to achieve optimal engine balance.