The quality of diesel is expressed in terms of

Options

A. octane number
B. decane number
C. ignition number
D. cetane number

Answer

To solve the question regarding how the quality of diesel is expressed, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Diesel Quality**: The quality of diesel fuel is an important factor that affects its performance in engines. Different metrics can be used to evaluate this quality.

2. **Identifying Relevant Terms**: The question provides four options: Octane number, Decane number, Ignition number, and Cetane number. We need to determine which of these is specifically used for diesel.

3. **Defining Cetane Number**: The Cetane number is a measure of the ignition quality of diesel fuel. It indicates how quickly and efficiently the fuel will ignite when injected into the engine's combustion chamber.

4. **Comparing with Other Terms**:
- **Octane Number**: This is used for gasoline (petrol) and measures the fuel's resistance to knocking.
- **Decane Number**: This is not commonly used in the context of diesel quality.
- **Ignition Number**: While it may sound relevant, it is not a standard term used to describe diesel quality.

5. **Conclusion**: Since the Cetane number directly relates to how quickly diesel fuel ignites when injected into hot compressed air, it is the correct measure for expressing the quality of diesel.

### Final Answer:
The quality of diesel is expressed in terms of **Cetane number**.

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