Question 11 OSE02 - Assistant Engineer - OSV

The Correct Answer is D **Explanation of why option D ("This is a two-stroke cycle, 60o V-type engine") is correct:** 1. **Engine Identification (Assumption based on Illustration MO-0163):** Illustration MO-0163 typically depicts a medium-speed diesel engine, very commonly used for propulsion or generator drive in anchor handling vessels (AHVs). While the illustration itself is not provided, this diagram (MO-0163) frequently refers to the **Electro-Motive Diesel (EMD) engine** series (such as the 645 or 710 series), or similar medium-speed engines often favored in the offshore industry for their robust power-to-weight ratio. 2. **Operating Cycle (Two-Stroke):** EMD engines are renowned for being **two-stroke cycle** diesel engines. Unlike most four-stroke engines which use valves for both intake and exhaust, EMD two-stroke engines typically feature **scavenging ports** near the bottom of the cylinder liner for intake air and **exhaust valves** (usually four) in the cylinder head for exhaust gas release. This design is characteristic of a high-power two-stroke cycle. 3. **Cylinder Configuration (60° V-type):** The standard V-angle configuration for EMD diesel engines (645 and 710 series) is **60 degrees**. This V-angle provides optimal balance and a relatively compact design for the specific firing order required by the two-stroke cycle. Therefore, the engine commonly associated with this illustration and used for generator drive in AHVs is a two-stroke cycle, 60° V-type engine. **Explanation of why the other options are incorrect:** * **A) This is a two-stroke cycle, 90o V-type engine:** While the operating cycle (two-stroke) is correct for the likely engine type (EMD), the standard V-angle for this specific engine family is 60°, not 90°. A 90° V-angle is more commonly associated with certain four-stroke or older engine designs where balance considerations differ. * **B) This is a four-stroke cycle, 90o V-type engine:** This is incorrect on both counts. The likely engine (EMD) is a two-stroke cycle, and the standard V-angle is 60°, not 90°. Most medium-speed marine engines are four-stroke, but the specific engine often referenced by MO-0163 is a two-stroke design. * **C) This is a four-stroke cycle, 60o V-type engine:** This is incorrect regarding the operating cycle. While the 60° V-angle is plausible for V-engines, the characteristic engine shown (EMD) operates on the two-stroke cycle, not the four-stroke cycle.