Motor fuels octane number

Protein Humidity/water content Hydrocarbons Carboxylic acids Amines Oil/fat Sucrose/glucose Additives in fuels Density Digestibility Viscosity Motor fuel octane number Reid vapor pressure of gasoline Seed germination Distillation parameters Fruit ripeness Total dissolved solids Particle size/fiber diameter Temperature Mechanical properties Thermal and mechanical pretreatment Molar masses of polymers... 

A motor fuel has an octane number X if it behaves under tightly defined experimental conditions the same as a mixture of X volume % of isooctane and (100 - X)% of n-heptane. The isooctane-heptane binary mixtures are called primary reference fuels. Octane numbers higher than 100 can also be defined the reference material is isooctane with small quantities of tetraethyl lead added the way in which this additive acts will be discussed later. 

In order to characterize the behavior of motor fuels or their components with regard to knocking resistance but without involving chemical composition criteria which are complex and not easy to quantify, the traditional method that has been universally employed for more than 50 years consists of introducing the concept of octane number. 

Measurement of octane numbers is carried out using a reference motor called CFR (Cooperative Fuel Research), referring to a series of studies conducted in 1928 in the United States in order to standardize the methods for characterizing motor fuels. 

The measurement error for conventional motor fuels is around 0.3 points and 0.7 points for the RON and the MON respectively. The RON is the characteristic more often used and more widespread than the MON moreover, when the octane number is used without reference either procedure, it is taken to be the RON. 

Specifications for octane numbers of motor fuels in France. 

The gradual reduction and ultimate elimination of lead has seen considerable effort by the refiner to maintain the octane numbers at satisfactory levels. In Europe, the conventional unleaded motor fuel, Eurosuper, should have a minimum RON of 95 and a minimum MON of 85. These values were set in 1983 as the result of a technical-economic study called RUFIT (Rational Utilization of Fuels in Private Transport). A compromise was then possible between refining energy expenses and vehicle fuel consumption (Anon., 1983). 

To the refiner, the question of octane numbers in future gasolines is of primary importance because it determines the course of operations, the development or on the contrary the stagnation of such and such a process. Table 5.12 thus gives an example of the typical composition by origin and concentration of different base constituents of three grades of the most common motor fuels distributed today in Europe conventional premium gasoline at 0.15 g Pb/1, Eurosuper and Superplus. 

If one talks henceforth about the necessity of matching an engine and its fuel, the demand for quality in motor fuels has, however, never ceased to be a preoccupation for refiners ever since gasoline became a commodity item. Two main classes of products are added to gasoline coming from refining octane number improvers and detergents. 

Motor fuels are submitted to strict regulations concerning physical properties and properties of combustion, for which the octane number is the most representative characteristic. 

Refiners will turn to reformulated motor fuels where the octane number will be increased by alkylate or oxygenated compounds. It has indeed been shown for a long time that oxygenated compounds, alcohols, ethers and ketones Improved the octane number of hydrocarbon-based blends (Whitcomb, 1975). 

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