Why was tetraethyl lead added to gasoline in the past?

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A periodic table element box for lead (Pb) shows atomic number 82, atomic weight 207.2, electron configuration, and labels for symbol, name, crystal structure, and physical state, with a legend for color and symbol meanings. — lead Properties of lead.

Tetraethyl lead (TEL) was added to gasoline primarily to serve as an antiknock agent. In the internal combustion process of a gasoline engine, certain fuel mixtures can ignite prematurely, causing a damaging and inefficient phenomenon known as "engine knock".1

When added to fuel, TEL decomposes in the engine's cylinders to form lead oxide, which regulates the combustion process and prevents this premature ignition. By stabilizing the fuel, TEL allowed for improved engine performance and efficiency.1

While this additive was effective for engine mechanics, it is important to recognize the severe ethical failure of prioritizing industrial performance over public health. The use of TEL resulted in widespread environmental contamination and lead poisoning, despite early warnings from health experts regarding its toxicity. The eventual global phase-out of leaded gasoline was a necessary step to protect human health and ensure the functionality of modern catalytic converters, which are essential for reducing harmful vehicle emissions.1