Aviation gasolines octane numbers

During World War II, isopropyl benzene, more commonly and commercially known as cumene, was manufactured in large volumes for use in aviation gasoline. The combination of a benzene ring and an iso-paraffin structure made for a very high octane number at a relatively cheap cost. After the war, the primary interest in cumene was to manufacture cumene hydroperoxide. This compound was used in small amounts as a catalyst in an early process of polymerizing butadiene with styrene to make synthetic rubber. Only by accident did someone discover that mild treating of cumene hydroperoxide with phosphoric acid resulted in the formation of... 

Antiknock gasoline a gasoline to which a low percentage of tetra-ethyl-lead, or similar compound, has been added to increase octane number and eliminate knocking. Such gasolines have an octane number of 100 or more and are now used chiefly as aviation fuel. 

Aviation gasoline contains a high concentration of alkylate and high-octane-number aromatics. Careful fractionation of virgin naphtha can also be performed to isolate isohexane and isoheptane fractions. Aromatic components are limited by their calorific value and are typically C and Cg. 

This value is primarily used to rate the antiknock values of aviation gasolines with octane numbers over 100. It is defined as the maximum knock-free power output obtained from fuel expressed as a percentage of the power obtainable from isooctane. The relationship between octane number and performance number is listed as follows ... 

Tetraethyl Lead - used to improve the octane number (antiknock) properties of gasoline. Use is mandatory in aviation gasoline. Tetraethyl lead is not permitted in civil and military jet fuel. 

Accdg to Riegel (Ref i, p 441), the 100-octane fuel for aircraft can be prepd by mixing iso-octane 40, aviation gasoline (74-octane number) 45 iso-pentane 15 S with 3cc tetraethyl lead. The iso-peQtane supplies (he... 

Pentane isomerization was carried out on a much smaller scale. Isopentane, because of its high octane number and good lead response, was blended directly into aviation gasoline. It also served to increase the volatility of blends containing such high-boiling components as alkylate. 

After the war the need for aviation alkylate declined rapidly, and most of the isomerization units closed down. During the motor gasoline octane race in the 1950 s, a number of butane isomerization units were placed on stream. Several pentane isomerization units were placed on stream in the 1960 s, and it is believed that only one or two plants today are being used to isomerize a C5/C6 straight run cut (41). 

Other tests have been used in the past, particularly for aviation gasoline, where it was more important to discriminate accurately between fuels with ON > 100. These had the advantage of being more related to real physical phenomena. For example, the performance number [11] was based on a single standard fuel, iso-octane, and the relative indicated mean effective power (imep) (defined in terms of the cylinder pressure [3]), and so is directly related to combustion. The performance number was 100 times the ratio of the knock limited imeps of the fuel and iso-octane. Much of the API 45 project on octane number of mixtures of pure hydrocarbons (see Section 7.2.5) was reported in terms of performance number. This project of the American Petroleum Institute ran from 1938 to 1957, and has provided an invaluable source of basic data. The articles by Lovell [10] and Scott [12] review and interpret these data. Whilst this criterion and these values of CCRs [10,13] are no longer in widespread use for automotive fuels, the data available in the older literature could still be useful in testing chemical models. Because the octane number scale is based on two reference fuels, modelling the octane number of any hydro-... 

During World War II, synthetic silica-alumina was found to be superior to activated-clay catalyst for production of aviation gasoline (51,347). The synthetic catalyst was more active and produced higher yields of fractions boiling within the aviation-gasoline range, higher octane number, and lower unsaturation. 

---