Lead was historically added to gasoline as tetraethyl lead (TEL) or ethylene bromide to improve the octane rating of the fuel and reduce engine knocking in internal combustion engines.

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Engine knocking is an undesirable phenomenon where the air-fuel mixture in the combustion chamber ignites prematurely, causing a sharp, metallic noise and potentially damaging the engine.

Reasons for Adding Lead to Gasoline:

Octane Boost:

Tetraethyl lead helped increase the octane rating of gasoline, which is a measure of its resistance to premature ignition or knocking. Higher-octane fuels are beneficial for high-compression engines, as they allow for more efficient combustion.

Engine Performance:

Lead additives were used to enhance engine performance, particularly in older engines designed to operate with leaded gasoline.

Wear Reduction:

Lead compounds were believed to provide lubricating properties, reducing wear and extending the lifespan of engine components.

Valve Seat Protection:

Lead served as a cushion between the exhaust valve and valve seat, helping prevent wear and deterioration in certain engine designs.

Phased Removal with Catalytic Converters:

The use of leaded gasoline began to decline in the 1970s and 1980s due to environmental and health concerns associated with lead emissions. Here are the key reasons for the removal of leaded gasoline, particularly with the widespread adoption of catalytic converters:

Catalytic Converter Incompatibility:

Lead is a catalyst poison, meaning it can deactivate the catalysts within catalytic converters. Catalytic converters are essential components in modern vehicles that help reduce emissions of harmful pollutants.

Air Quality Concerns:

Lead is a potent environmental toxin, and its combustion in engines led to the release of lead compounds into the atmosphere. Inhalation of lead compounds poses serious health risks, especially for children, leading to concerns about air quality and public health.

Regulatory Measures:

Environmental regulations, such as the Clean Air Act in the United States, mandated the phase-out of leaded gasoline to reduce air pollution and protect public health.

Shift to Unleaded Gasoline:

As a response to regulatory requirements and environmental awareness, the automotive industry transitioned to the use of unleaded gasoline, which became more widely available and compatible with catalytic converters.

Improved Engine Designs:

Advances in engine technology and design, along with the development of alternative additives and fuel formulations, allowed for the production of high-performance engines without the need for leaded gasoline.

Today, leaded gasoline is virtually obsolete in most parts of the world. Unleaded gasoline, along with catalytic converters and other emission control technologies, has become the standard for reducing air pollution and protecting both human health and the environment.