Shell for anti-knock

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.


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:
Shell historical archives.

Decarbonising Aviation: Cleared for Take-off

Our new report, produced with Deloitte, reflects views from right across the aviation industry on the obstacles the sector faces and provides a clear pathway for the sector to accelerate progress towards net-zero emissions.

Download your copy

Work with us today for a low carbon future

Shell has supported the pioneers of aviation for over 100 years. Share your challenge and let’s work together today for a sustainable tomorrow.

Share your challenge

Our Stories

FIDO clears the way for safer landings

Shell Aviation supports British Airforce in developing fog dispersal systems for safer landings.

Well to wing quality assurance

Shell’s rigorous assurance system guarantees the quality of aviation fuel from refinery to aircraft tanks.

Solving the kerosene fungus problem

Shell tackles fuel contamination issue for Asian airports.

Safety added as standard

New Shell additive stops static build-up, preventing potential explosions and fires in fuel tanks.

Shell grade monitor improves fuel safety

Fail-safe automatic system helps prevents fuel contamination.