Octane Number and Cetane Number – Importance | New Topic [2024]

In this note, we will learn a topic called “About Octane Number and Cetane Number” and Its Importance and Ratings. Welcome to Poly Notes Hub, a leading destination for Engineering Notes for Diploma and Degree Engineering Students.

Author Name: Arun Paul.

Octane Number and Cetane Number

1. Petrol (Gasoline) – Octane Number

• Definition: The octane number measures a fuel’s capacity to resist knocking during combustion in engines with spark ignition.
• Importance: A higher octane rating indicates more resistance to early ignition, which is essential for powerful engines.
• Typical Octane Ratings:
  • Regular Petrol: 87 octane (common in countries like the US).
  • Premium Petrol: 91–98 octane (recommended for high-compression engines, sports cars, or luxury vehicles).
  • Racing Fuel: 100+ octane (used in specialized engines).

2. Diesel – Cetane Number

• Definition: The cetane number determines how easily diesel fuel ignites in compression-ignition engines.
• Importance: A greater cetane number leads to smoother combustion, improved cold start performance, and lower emissions.
• Typical Cetane Ratings:
  • Standard Diesel: 40–55 cetane (varies by region and grade).
  • Premium Diesel: 55+ cetane (offers enhanced performance and reduced engine noise).