Question

Cetane number is important test for:

• A. Gasoline
• B. Kerosene
• C. High speed diesel oil
• D. Fuel oil

Hint:

Remember this fundamental contrast in fuel chemistry:
Diesel fuel \(\to\) Cetane Number (measures ease of auto-ignition; higher is better for diesel).
Gasoline fuel \(\to\) Octane Number (measures resistance to auto-ignition; higher is better for gasoline).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks us to identify the specific fuel for which the "cetane number" is a critical performance and quality test parameter.
Different fuels have different combustion characteristics depending on the engine design (spark-ignition versus compression-ignition).

Step 2: Key Formula or Approach:
1. Spark-ignition engines (such as gasoline engines) require fuels that resist auto-ignition to prevent engine knocking. This resistance is measured by the Octane Number.
2. Compression-ignition engines (such as diesel engines) require fuels that auto-ignite readily when sprayed into the hot compressed air in the cylinder. This ease of auto-ignition (ignition delay) is measured by the Cetane Number.

Step 3: Detailed Explanation:
Let us analyze the significance of the Cetane Number for the options provided:
- The Cetane Number of a fuel is determined by comparing its ignition delay to a reference blend of n-cetane (hexadecane, which has a cetane number of 100) and heptamethylnonane (which has a cetane number of 15).
- High speed diesel oil is used in high-speed compression-ignition diesel engines, where the window of time for air-fuel mixing and ignition is extremely short.
- Therefore, high speed diesel must have a high cetane number (typically between \(40\) and \(55\)) to minimize the ignition delay, ensuring smooth and complete combustion, reducing smoke, and preventing diesel knock.
- Gasoline is used in spark-ignition engines where auto-ignition is undesirable, so its quality is measured by the octane rating rather than the cetane number.
- Kerosene is primarily used as aviation turbine fuel or heating fuel, where cetane number is not the primary specification.
- Fuel oil is a heavy residue fuel used in large boilers or slow marine engines where ignition delay is less critical due to low engine speeds.
Therefore, the cetane number is a vital test specifically for high speed diesel oil.

Step 4: Final Answer
Thus, the cetane number is an important test for high speed diesel oil, corresponding to option (C).