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The Development of Shell 
100-Octane Gasoline

A new era in aviation began when 100-Octane gasoline was developed and became available in commercial quantities. The story of this super-fuel is one of the great dramas of industrial science. It has been an important factor in improving airplane performance and has helped establish records in the Bendix and other important aviation events.

For the past ten years, aircraft engine design and construction have been steadily improving, resulting in greatly increased power output per unit weight and decreased specific fuel consumption by the utilization of higher compression ratios and efficient forced induction systems. This development leading to our present-day high output engine has been greatly contingent upon and limited by the development and availability of improved fuels, the most important requisite of which is anti-knock value.

Horsepower output has increased by roughly 33 1/3% per unit weight with a corresponding increase in anti-knock value of fuels from 73-octane to 87-octane for commercial grades. This increase has been accomplished through the addition of anti-knock compounds to regular straight run aviation gasoline having an initial knock-rating of 73-octane as required by the leading engine manufacturers. Until the development of 100-octane fuel, the highest grade specified by the Air Corps was 92-octane, determined by the special Army test method which rates straight run aviation gasoline slightly better than the A.S.T.M method used to test commercial fuels. Consequently, Army grade 92-octane has a rating only slightly higher than the commercial grade 87. When both products are tested by the same method, there is a difference of not more than two octane numbers.

Extensive research work was done on iso-octane (initial knock rating 100) by Shell Oil Company in anticipation of the demand for improved fuels for military and commercial purposes. Tests were made to determine whether the advantages of the new fuels were commensurate with the additional costs, based on the probably price after the creation of a potential market for such fuels.

This led to the commercial development of Shell 100-Octane Gasoline with the Army and Navy as prospective consumers.

The Air Corps' first development work on 100-octane fuel was conducted by the Power Plant Branch at Wright Field, Dayton, Ohio.

Roughly, the tests showed that a 25% increase in power output could be obtained through the use of 100-octane fuels as compared to 92-octane in the same engine operating under similar controlled conditions. In order to utilize the advantages of 100-octane fuel, engines with an extremely high degree of supercharge capacity were employed. Subsequently, engines designed specially for operation on 100-octane fuel will make possible still greater increases in performances.

Since these tests, the Air Corps has found the use of this fuel highly advantageous for testing military planes. In one case, it was essential to determine the high speed of a pursuit plane over the speed course. Full throttle operation was only possible with 100-octane fuel. Another case, showing excessive engine overheating during maximum climb test, was successfully completed with the use of 100-octane, accompanied by a 30 degree Centigrade decrease in cylinder-head temperature.

Realizing that further development of high output engines was contingent upon the procurement of 100-octane aviation gasoline, the Air Corps prepared specifications for such a fuel which has since been supplied by Shell in large quantities.

As the possibilities of 100-octane fuel unfolded Shell's experimental equipment at Martinez Refinery was supplemented by a large scale iso-octane plant capable of producing this fuel in commercial quantities. The plant consists of polymerization and hydrogenation units, and iso-octane, formerly valued at $16 to $20 per gallon and used only as a high anti-knock standard reference fuel, is now one of the components of Shell 100-Octane Gasoline which is available to government fighting forces and commercial planes for everyday flying at a nominal premium.

Advantages of this fuel have become more apparent as engines are designed to fully utilize it. It is estimated that with such power plants and fuel, a present-day 14-passenger transport plane would have about 700-pound greater payload due to the saving power plant weights and reduced fuel consumption. This would increase the payload of such a transport by three passengers and considerable weight of cargo, resulting in increased revenue to the operator. Up to 15% decrease in specific fuel consumption is possible with 100-octane fuel compared to commercial grade 87 or Army grade 92.This would reduce it from a satisfactory average consumption in present-day engines from .45 to .38 pounds of fuel per B.H.P. hour, thereby approaching the efficiency of the Diesel cycle.

The regaining of the world's speed record for land planes by the United States was facilitated by the use of 100-octane fuel. The excessive engine overload encountered would not have been possible with 87-octane fuel as serious detonation would have undoubtedly occurred resulting in engine failure.