Octane rating

Octane rating or octane number is a standard measure of the performance of an engine or aviation gasoline. The octane number is a value used to indicate the resistance of a petroleum product to knocking (a rattling noise indicative of self-ignition) in spark-ignition internal combustion engines.

History

The octane rating system was developed by the chemist Russell Marker. It was introduced in the year 1926. The need for a method to measure the resistance of fuel to knocking was felt due to the development of higher compression engines.

Measurement

Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isooctane) and heptane. An 87-octane gasoline, for example, performs the same as a blend of 87% isooctane and 13% heptane.

Types of Octane Ratings

There are different types of octane ratings: Research Octane Number (RON), Motor Octane Number (MON), and Anti-Knock Index (AKI).

Research Octane Number (RON)

The RON method measures the resistance of a fuel to knocking or pinging during a test in a single-cylinder test engine.

Motor Octane Number (MON)

The MON testing method uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance.

Anti-Knock Index (AKI)

In most countries, including Australia, New Zealand and all of those in Europe, the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2.

Importance

The octane rating of fuel is very important as it directly impacts the fuel efficiency and performance of the engine. Higher octane fuels are used in high performance gasoline engines.

See also

• Cetane number
• Fuel efficiency
• Gasoline