Question 20 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is B **Explanation of why option B ("Cetane rating") is correct:** The cetane rating (or cetane number) is the primary standardized measure used to quantify the ignition quality of diesel fuel. Ignition quality refers to how readily the fuel will auto-ignite and combust when injected into the hot, compressed air within a diesel engine cylinder. A higher cetane rating indicates a shorter ignition delay—meaning the fuel ignites more quickly and efficiently, leading to smoother, more complete combustion and better engine performance, especially during starting and under varying loads. **Explanation of why the other options are incorrect:** * **A) Heating value:** The heating value (or calorific value) measures the energy content of the fuel (how much heat is released upon combustion). While important for determining fuel efficiency (economy), it is not a direct measure of **ignition quality** (the speed or readiness of ignition). * **C) Viscosity:** Viscosity measures the fuel's resistance to flow. It is critical for proper atomization (how the fuel sprays into the cylinder) and for lubricating fuel system components (like pumps and injectors). However, it does not directly measure the chemical properties governing the **ignition delay** or quality. * **D) Density:** Density measures the mass per unit volume of the fuel. It is important for bunkering calculations and can influence the energy content delivered per volume (since commercial fuel is bought by volume). Like viscosity, it affects physical handling and metering but is not a measure of the chemical **ignition quality**.