Question 2 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is C **Why Option C is Correct:** Option C states: "Diesel engines are reciprocating, internal combustion engines using the heat of compression to achieve ignition." 1. **Reciprocating:** Diesel engines utilize pistons that move back and forth (up and down) within cylinders. This back-and-forth motion is defined as reciprocating motion. 2. **Internal Combustion:** The combustion (burning of fuel) occurs inside the engine's working cylinders, making it an internal combustion engine (ICE), as opposed to an external combustion engine (like a steam engine). 3. **Heat of Compression for Ignition:** The fundamental principle of a diesel engine (Compression-Ignition or CI engine) is that air is heavily compressed in the cylinder. This rapid compression generates extremely high temperatures (the heat of compression). When fuel is injected into this superheated air, it immediately ignites without the need for an external spark plug. **Why the Other Options are Incorrect:** * **A) Diesel engines are reciprocating, internal combustion engines using an electric spark to achieve ignition.** * **Incorrect:** While they are reciprocating and internal combustion, they do *not* use an electric spark for ignition. Engines that use a spark plug for ignition are called spark-ignition (SI) engines (e.g., gasoline engines). * **B) Diesel engines are rotary, internal combustion engines using the heat of compression to achieve ignition.** * **Incorrect:** Diesel engines are generally **reciprocating** (piston-based), not rotary. A common example of a rotary engine is the Wankel engine, which is not typically used for heavy marine propulsion like tugboats and usually operates on the spark-ignition principle. * **D) Diesel engines are reciprocating, external combustion engines using the heat of compression to achieve ignition.** * **Incorrect:** Diesel engines are **internal** combustion engines. In an external combustion engine (ECE), such as a steam turbine, the fuel is burned outside the power-generating cylinders/chambers.