Katerina Swanson
Leaded fuel, also known as tetraethyl lead (TEL), was once commonly used in automobiles due to its ability to improve engine performance and increase fuel efficiency. TEL was introduced to gasoline in 1921 by a research division of Dayton Metal Products Co. and General Motors. Over time, concerns arose regarding the toxic effects of lead on human health and the environment, leading to a gradual phase-out of leaded gasoline in many countries. The phase-out was driven by the introduction of catalytic converters, which were mandated in the United States for 1975 and later models to meet tighter emissions regulations. While most modern cars have transitioned to unleaded fuel, some older vehicles, particularly classic cars, may still require leaded fuel or lead additives to prevent engine issues such as valve seat wear and microwelds. However, exemptions for the use of leaded fuel are becoming less common due to the health and environmental risks associated with lead toxicity.
Characteristics and Values Table for Leaded Fuel in Cars
| Characteristics | Values |
|---|---|
| Boosted octane rating | Allowed for higher compression ratios |
| Reduced knocking | Eliminated the ever-present "knock" caused by auto-ignition of fuel being compressed past its ignition temperature |
| Reduced wear on valve seats | Prevented "microwelds" from forming between the hot valve surfaces and the seats in the cylinder head as the valve closed |
| Improved lubrication | Helped fuel ignite only when appropriate on the power stroke, thus helping eliminate exhaust valve wear and tear |
| Phase-out | Completed by the early 2000s in most industrialized countries due to concerns over lead levels in air and soil, and the neurotoxicity of lead |
| Banned | California in 1992, the rest of the US in 1996, Japan in 1986, and the EU and UK in 1993 |
| Exemptions | Owners of classic cars designed to run on leaded fuel; aviation fuel |
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What You'll Learn
Tetraethyl lead (TEL) boosts the octane rating
TEL was first added to fuel in 1921 by a research division formed by the merger of Dayton Metal Products Co. and General Motors. The addition of TEL to fuel allowed manufacturers to produce much cheaper grades of fuel while still maintaining the needed octane ratings that a car’s engine required. This also helped eliminate wear and tear on exhaust valves by preventing "microwelds" from forming between the hot valve surfaces and the seats in the cylinder head as the valve closed.
Over time, other methods for achieving higher octane ratings without the use of TEL were discovered. Safer methods for making higher-octane blending stocks such as reformate and iso-octane reduced the need to rely on TEL, as did other antiknock additives of varying toxicity including metallic compounds such as methylcyclopentadienyl manganese tricarbonyl (MMT) and oxygenates including methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME), and ethyl tert-butyl ether (ETBE).
Due to concerns about the toxicity of lead and its interference with catalytic converters, which use a chemical reaction to change pollutants like carbon monoxide and other harmful hydrocarbons into carbon dioxide, nitrogen, and water, a phase-out of TEL from road vehicle fuels was completed in most industrialized countries by the early 2000s. The first country to completely ban leaded gasoline was Japan in 1986, and since 1993 all gasoline-powered cars sold in the European Union and the United Kingdom have been required to use unleaded fuel. Today, lead substitutes use a variety of proprietary formulas, often based on manganese, sodium, phosphate, or iron, to fulfill the function of lead without the toxic side effects and harm to catalytic converters.
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TEL reduces engine knocking
Engine knocking or 'knock' occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The shock wave creates a characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.
TEL, or tetraethyl lead, is a soluble organolead compound added to gasoline that was common until it was discontinued for reasons of toxic pollution. TEL works to reduce engine knocking by retarding the pre-flame reaction at the flame front, which reduces the temperature and pressure build-up in the end gas zone, which in turn reduces the tendency of the end gas to auto-ignite. When the temperatures of the pre-flame reaction are reduced by TEL, the tendency of knocking is reduced.
TEL was added to fuel to improve the octane rating of the gas, allowing manufacturers to produce much cheaper grades of fuel while still maintaining the needed octane ratings that a car’s engine required. Another benefit of TEL was that it kept valve seats from becoming prematurely worn down. Exhaust valves, in early model cars, that were subject to engine knocking tended to get micro-welds that would get pulled apart on opening, resulting in rough valve seats and premature failure. TEL helped fuel ignite only when appropriate on the power stroke, thus helping eliminate exhaust valve wear and tear.
TEL was phased out of most road vehicle fuels in industrialized countries by the early 2000s due to concerns over air and soil lead levels and the accumulative neurotoxicity of lead. The use of catalytic converters, mandated in the United States for 1975 and later model-year cars, started a gradual phase-out of leaded gasoline in the U.S. Advances in automotive engineering and petroleum chemistry also lessened the need for TEL. Safer methods for making higher-octane blending stocks such as reformate and iso-octane reduced reliance on TEL, as did other antiknock additives.
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TEL reduces valve seat wear
TEL, or tetraethyl lead, was added to fuel to prevent engine knocking and improve octane ratings. Engine knocking occurs when fuel is compressed past its ignition temperature, causing auto-ignition. This knocking results in micro-welds in the exhaust valves, which then get pulled apart when the valves open, leading to rough valve seats and premature failure.
TEL was first introduced in 1921 by chemists at General Motors to address the need for high-compression engines and the insufficient fuel supply to run them. By adding lead to fuel, manufacturers could improve the octane rating of the gas, allowing them to produce cheaper grades of fuel while still meeting the required octane ratings.
TEL also played a role in reducing valve seat wear. The lead in the fuel helped to eliminate exhaust valve wear and tear by preventing auto-ignition and ensuring that the fuel ignited only when appropriate on the power stroke. This prevented the micro-welds and valve seat issues caused by engine knocking.
However, concerns about the environmental and health hazards of leaded gasoline led to its gradual phase-out starting in the 1970s. The use of catalytic converters and advancements in automotive engineering and petroleum chemistry reduced the need for TEL. Today, alternative antiknock additives, such as metallic compounds and oxygenates, are used instead of TEL to improve octane ratings and reduce valve seat wear.
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TEL is toxic and harmful to the environment
TEL, or tetraethyl lead, was added to fuel to improve the octane rating of the gas, allowing manufacturers to produce much cheaper grades of fuel while still maintaining the needed octane ratings that a car’s engine required. However, TEL is toxic and harmful to the environment.
TEL is a heavy metal, and these types of metals are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They can cause cellular and tissue damage, leading to a variety of adverse health effects and human diseases. The toxicity of heavy metals depends on several factors, including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals.
In the human body, exposure to TEL can occur through breathing, eating, or touching soil, water, food, or air that contains this chemical. The amount of TEL in these mediums is called its concentration, and the higher the concentration, the more likely health effects will occur. Even a small amount of TEL, 6 mL, is enough to induce severe lead poisoning.
The use of TEL in road vehicle fuels has been phased out in most industrialized countries due to concerns over air and soil lead levels and the accumulative neurotoxicity of lead. The first country to completely ban leaded gasoline was Japan in 1986, and since 1993, all gasoline-powered cars sold in the European Union and the United Kingdom have been required to use unleaded fuel. The phase-out of TEL has been a gradual process, with leaded gasoline still available in some countries as of the early 2010s.
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Alternatives to TEL exist
Improvements in automotive engineering and petroleum chemistry have lessened the need for TEL. For example, the use of catalytic converters, mandated in the United States for 1975 and later model-year cars, helped phase out leaded gasoline. Catalytic converters use a chemical reaction to convert harmful pollutants like carbon monoxide and hydrocarbons into less harmful carbon dioxide, nitrogen, and water.
Furthermore, ethanol, a high-percentage additive, has been established as an effective antiknock agent since 1921. However, TEL was introduced for commercial reasons, as large volumes of ethanol were needed to meet the demands of a growing fuel-hungry society.
The phase-out of TEL from road vehicle fuels was completed in most industrialized countries by the early 2000s due to concerns about lead levels in the air, soil, and its accumulative neurotoxicity. Japan became the first country to completely ban leaded gasoline in 1986, and since 1993, all gasoline-powered cars sold in the European Union and the United Kingdom have been required to use unleaded fuel.
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Frequently asked questions
Leaded fuel was used in cars to boost the octane rating, allowing for higher compression ratios, reducing knocking, and minimizing wear on the valve seats.
Leaded fuel has been found to be dangerous to people and the environment. It contributes to air pollution and can cause health issues such as brain damage and severe lead poisoning.
The phase-out of leaded fuel began in the mid-1970s due to concerns about the toxicity of lead and its interference with catalytic converters. The first country to completely ban leaded gasoline was Japan in 1986.
Classic cars that were designed to run on leaded fuel often require modifications to be compatible with unleaded fuel. These modifications may include installing hardened exhaust valves and seats, and adjusting compression ratios. However, many classic car owners choose to use lead substitutes or lead additives to avoid potential engine damage.
