When TEL (Tetra Ethyl Lead) is added to petrol, then:

The correct answer is it increases the anti-knocking rating.

Key Points

• Tetraethyl lead (TEL) was commonly added to petrol to improve its anti-knocking properties.
• Anti-knocking properties help in preventing engine knocking, which is caused by premature ignition of the fuel-air mixture.
• The addition of TEL increases the octane rating of petrol, making it burn more smoothly.
• Higher octane ratings allow engines to run at higher compression ratios without knocking.
• Due to environmental and health concerns, the use of TEL has been largely phased out globally.

Additional Information

• Engine Knocking:
  • Engine knocking is a noise resulting from premature combustion of the fuel-air mixture in the engine cylinders.
  • This premature combustion can lead to damage to the engine over time.
  • Knocking is more prevalent in engines with lower octane fuel.
• Octane Rating:
  • The octane rating is a standard measure of a fuel's ability to resist knocking during combustion.
  • Higher octane ratings indicate better resistance to knocking.
  • Premium fuels usually have higher octane ratings compared to regular fuels.
• Environmental Impact of TEL:
  • TEL releases lead into the environment, which is toxic and can cause health issues.
  • Due to its adverse effects, many countries have banned the use of leaded petrol.
  • Alternatives like ethanol and MTBE are now used to increase octane ratings without harmful effects.
• Alternative Anti-Knocking Agents:
  • Ethanol is used as an additive to increase octane ratings and reduce knocking.
  • Methyl tertiary-butyl ether (MTBE) is another common additive used as an anti-knocking agent.
  • These alternatives are considered safer and environmentally friendly compared to TEL.