What Is an Octane Rating?

Octane number (Octane Number) is an indicator of the resistance of the fuel (gasoline) used by vehicles to knocking. There are many kinds of hydrocarbons in gasoline. Among them, n-heptane is more likely to cause spontaneous combustion at high temperatures and pressures, causing knocking, reducing engine efficiency, and more likely to cause overheating of the cylinder walls and even piston cracking. Therefore, the n-heptane has an octane number of zero, and isooctane has a small explosion phenomenon, and its octane number is set to 100. Other hydrocarbons also have different octane numbers, which may be less than 0 (such as n-octane) or greater than 100 (such as toluene). Therefore, the octane number in gasoline depends directly on the proportion of various hydrocarbons in the gasoline. ^[1]

Currently testing vehicle gasoline

fuel	Research Method Octane Number	Motor law octane number	Violence
Cetane	<-30
N-octane	-10
N-heptane	0
Diesel	15-25
Isooctane	100	90-92	95-96
E10 gasoline	87-93
E85 gasoline	105
Methane	107

Motor gasoline grades are distinguished by octane number. There are 66, 70, 76, 80, 85 and so on. For example, the gasoline of No. 70 vehicle indicates that the gasoline has an octane number of not less than 70. According to the actual measurement results of the octane number, it can be determined which brand of automobile gasoline it belongs to. ^[5]

Different chemical structures

To increase the octane number, anti-knock agents can be used. Anti-knock agent, also known as anti-knock agent, gasoline anti-knock agent, octane enhancer. It is a kind of high molecular polymer used to increase the octane number to prevent or reduce the knock produced when gasoline is burned in the engine. Among them, alkyl lead began to become a widely used anti-knock agent in 1923. In addition, tetramethyl lead, tetraethyl lead and mixtures thereof are also often used. However, such lead-containing anti-knock agents can cause harmful long bodies that pollute the air. Therefore, in unleaded gasoline, other types of anti-explosion agents, such as methylcyclopentadiene tricarbonyl manganese (MMT) Anti-knock agent of manganese compounds.

At present, the main measures for increasing the octane number of gasoline are to adopt advanced refining processes and use high-octane blending agents, such as adding methyl tert-butyl ether, ethyl tert-butyl ether or alcohol fuels. ^[7]