Question 8 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is C ### Why Option C is Correct The context of a mollusc dredger, particularly one fitted with generator set drive engines, strongly suggests the use of medium- or high-speed diesel engines commonly employed in marine auxiliary and power generation roles. These engines are typically four-stroke, direct-injection (DI) engines. 1. **Open Type Combustion Chamber (Direct Injection):** This design is characterized by the fuel being injected directly into the main combustion space formed between the cylinder head and the piston crown (the 'open' chamber). This method is highly efficient, offers easier cold starting, and is standard for modern, higher-output diesel engines used in this application. 2. **Flat Fire-Deck:** The "fire-deck" refers to the bottom surface of the cylinder head, which faces the piston. In direct-injection engines, the majority of the combustion chamber shape is actually formed by a deep recess (often toroidal or bowl-shaped) in the piston crown. To maximize efficiency and simplify manufacture in such designs, the surface of the cylinder head (the fire-deck) is typically flat, allowing for optimal seating of valves and a central location for the fuel injector. Therefore, the most likely and standard configuration for a generator set drive engine of this type is an open combustion chamber with a flat cylinder head face. ### Why Other Options Are Incorrect **A) The engine uses pre-combustion chambers with a flat fire-deck.** * **Incorrect:** Pre-combustion chambers (indirect injection, IDI) utilize a small, separate chamber where combustion is initiated before spreading to the main cylinder. This design is less common in modern, medium-to-large high-speed marine generator engines because it results in higher heat losses, lower thermal efficiency, and increased fuel consumption compared to direct injection (open chamber) designs. **B) The engine uses turbulence chambers with a hemispherical fire-deck.** * **Incorrect:** Turbulence chambers (a type of IDI engine, like a swirl chamber) were used to promote air movement to mix effectively with the fuel spray, particularly in older or smaller high-speed engines. A hemispherical fire-deck (cylinder head surface) is characteristic of older overhead valve (OHV) gasoline engines or specific IDI designs, but it is not the standard efficient configuration for modern, large-bore direct-injection diesel generator sets. **D) The engine uses an open type combustion chamber with a hemispherical fire-deck.** * **Incorrect:** While the engine uses an open type combustion chamber, the fire-deck (the cylinder head face) is typically flat in modern direct-injection diesels. A hemispherical fire-deck would necessitate a complex piston shape to achieve the necessary compression ratio and usually complicates valve design and injector placement without providing the efficiency benefits of a flat-deck/bowled-piston design in this application.