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For the car driver and private pilot of today, the idea that their engines might ‘knock’ or ‘pink’ would produce a bemused reaction. Yet for early engines, first for automobiles and then for aeroplanes, it was a common problem.

‘Knocking’ occurs during the compression stage in the engine cylinder where spontaneous and premature fuel ignition takes place. The result can be audible – hence knocking – reducing power and can damage engines, even causing failure.

Following the First World War, important developments in the quality and refining of aviation fuel were taking place. Shell had initially supplied aircraft with regular Shell Motor Spirit, the same fuel (or a slightly improved version) that was used for cars. By 1919, it had developed Shell Aviation Spirit, an improved fuel better tailored for an aircraft engine. But knocking still remained a real safety issue.

The same year, Sir Robert Waley-Cohen of the Asiatic Petroleum Company (Shell) hired English engineer Harry Ricardo, the famous pioneer of the internal combustion engine to help solve the knocking problem. Extensive research and testing by the Shell/Ricardo team led to a measurable definition of the anti-knock properties of fuel, expressed in the ‘octane number’ which was introduced as a quality standard for fuels. The higher the octane number, the more compression the fuel can withstand before detonating.

The development of higher quality fuels, with the appropriate octane number and thus high anti-knock characteristics was critical for aircraft engine performance and the advancement of aviation safety. Throughout the 1920s and 1930s, Shell used the findings of this research to improve the quality of its aviation fuel, and by 1934, a new fuel – octane 100 – was produced, significantly improving the output of aircraft engines. Many modern aviation fuels use the same octane rating to this day.

Since then, Shell Aviation has continued to support the aviation industry to ensure fuel safety. One example is the Shell Water Detector, a simple and economical device for sampling fuel to detect water contamination, introduced in 1957. It soon became the industry standard and is still widely used today.

Sources:

_{R. van Egmond and A. Westra, Shell and aviation. The story of more than a century of collaboration. Shell International B.V., 2019, p. 48-51.
Shell Aviation News, 1957, number 224, p.20.
Shell website: /business-customers/aviation/aviation-fuel/shells-water-detector-tool.html.
Shell historical archives.}