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Which of the following statements about a petrol engine's octane and cetane rating is TRUE?

Which of the following statements about a petrol engine's octane and cetane rating is TRUE? Correct Answer Diesel should have lower octane but higher cetane number

Concept:

  • Octane Number (ON) is the measure of the resistance of gasoline to detonation or preignition of the fuel in the SI engine.
  • It is measured relative to the mixture of iso-octane (2, 2, 4 trimethyl pentane) (ON = 100) and n-heptane with (ON = 0).
  • Higher octane fuel has a greater resistance to autoignition under higher combustion pressure and heat.
  • Cetane Number (CN) is the measure of the combustion quality of diesel oil or it is the measure of the ignition delay.
  • The cetane number is calculated by determining rich mixture of cetane (hexadecane)(CN = 100) and iso-cetane (CN = 0).
  • The main difference between the cetane and octane number of a fuel is that the octane rating represents how well a fuel can resist pre-ignition due to compression which ensures that the fuel ignites only from a spark from the spark plug.
  • However, the cetane number measures the delay in the ignition time of the fuel.
  • Hence, both numbers are inversely related to each other and a fuel having high octane number will have a low cetane number and vice-versa.

Here, Diesel should have lower octane but higher cetane number

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