Question 64 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is D **Why Option D is Correct:** Option D states that diesel engines are **reciprocating, internal combustion engines using the heat of compression to achieve ignition.** 1. **Reciprocating:** Standard diesel engines (like those used on tugboats) use pistons that move back and forth (reciprocate) within cylinders to convert pressure into rotational motion. 2. **Internal Combustion:** The combustion (burning) of the fuel occurs *inside* the engine cylinder itself, defining it as an internal combustion engine (ICE). 3. **Heat of Compression (Compression Ignition):** The defining characteristic of a diesel engine is how ignition occurs. Air is compressed to a very high pressure, which raises its temperature significantly (adiabatic heating). When fuel is injected into this superheated air, it immediately ignites without needing an external spark plug. This process is called compression ignition (CI). **Why Options A, B, and C are Incorrect:** * **A) Diesel engines are rotary, internal combustion engines using the heat of compression to achieve ignition.** * **Incorrect Element:** Diesel engines are typically **reciprocating**, not rotary (rotary engines, like the Wankel engine, have a fundamentally different mechanical design and are rare in heavy-duty applications like tugboats). * **B) Diesel engines are reciprocating, external combustion engines using the heat of compression to achieve ignition.** * **Incorrect Element:** Diesel engines are **internal combustion** engines. An external combustion engine (ECE), such as a steam engine, burns the fuel outside the main working cylinders. * **C) Diesel engines are reciprocating, internal combustion engines using an electric spark to achieve ignition.** * **Incorrect Element:** Engines that use an electric spark to achieve ignition are **gasoline engines** (spark-ignition or SI engines). Diesel engines use **compression ignition**.