Octane Rating
Antiknock Quality of the Gasoline

Octane rating defines the gasoline antiknock quality (resistance to pre-ignition). The higher the octane rating, the greater the resistance to engine knock. Two differing procedures are in international use for determining the octane rating; these are the Research Method and the Motor Method (DIN 51 756; ASTM D 2699 and ASTM D 2700).

Research Octane Number (RON) & Motor Octane Number (MON)

The number determined in testing using the Research Method is the Research Octane Number, or RON. Research Octane Number (RON) serves as the essential index of acceleration knock.

The Motor Octane Number, or MON, is derived from testing according to the Motor Method. Motor Octane Number (MON) basically provides an indication of the tendency to knock at high speeds.

The Motor Method differs from the Research Method by using preheated mixtures, higher engine speeds and variable ignition timing, thereby placing more stringent thermal demands on the fuel under examination. Motor Octane Number (MON) figures are lower than those of Research Octane Number (RON).

Octane number up to 100 indicate the volumetric content in percent of C8H18 iso-octane (trimethyl pentane) contained in a mixture with C7H16 n-heptane at the point where the mixture's knock resistance in a test engine is identical to that of the fuel being tested. Iso-octane, which is extremely knock resistant, is assigned the octane number 100 (100 RON and MON), while n-heptane, with low-resistance to pre-ignition, is assigned octane number 0.