State any 2 reasons for using ethyl alcohol as a SI engine fuel.

 Here are two key reasons for using ethyl alcohol (ethanol) as a fuel in SI (Spark Ignition) engines:


1. High Octane Number

  • Ethanol has a high octane rating (≈ 108), which allows it to resist engine knock (pre-ignition or detonation).

  • This enables higher compression ratios in SI engines, leading to better efficiency and performance.


2. Renewable and Cleaner Burning

  • Ethanol is a renewable biofuel, typically produced from crops like sugarcane or corn.

  • It burns cleaner than gasoline, producing less CO and unburnt hydrocarbons, and lower net CO₂ emissions (due to carbon neutrality from plant sources).


✳️ Bonus Benefits:

  • Provides cooling effect due to high latent heat of vaporization.

  • Can be blended with gasoline (e.g., E10, E85) to reduce petroleum consumption.


Ethanol is increasingly used in modern SI engines, especially in flex-fuel vehicles and biofuel initiatives for sustainable energy.

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