Which of the following statements regarding fuel auto-ignition and anti-knock ratings is/are correct?
Options:
(A) Cetane number measures the self-ignition quality and shortness of ignition delay for diesel fuels.
(B) Pure n-hexadecane (cetane) is assigned a cetane rating of 100, while alpha-methylnaphthalene is assigned 0 (or heptamethylnonane is assigned 15).
(C) Iso-octane (2,2,4-trimethylpentane) has high resistance to auto-ignition and is assigned an octane rating of 100.
(D) Fuels that have high octane numbers naturally possess high cetane numbers.
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
• Cetane rating measures ignition ease in CI engines (A is correct).
• Standard reference fuels for cetane are n-hexadecane (100) and isocetane/alpha-methylnaphthalene (B is correct).
• Iso-octane resists knock in SI engines and defines 100 octane (C is correct).
• Octane and cetane scales are inverse: fuels with high resistance to auto-ignition (high octane) have very long ignition delay (low cetane) (D is false).