ANS:A - very low which prevents their ignition by compression.

Alcohols are not suitable as diesel engine fuel primarily because of their low cetane number, which prevents their ignition by compression. Explanation:

• The cetane number is a measure of the ignition quality of diesel fuel during compression ignition in diesel engines. A higher cetane number indicates better ignition quality, meaning the fuel ignites more easily and quickly when injected into the combustion chamber.
• Alcohols generally have very low cetane numbers compared to conventional diesel fuels derived from petroleum.
• Due to their low cetane numbers, alcohols tend to have poor ignition characteristics in diesel engines, leading to issues like long ignition delay, incomplete combustion, and reduced engine performance.
• Therefore, alcohols are not suitable as direct substitutes for diesel fuel in compression ignition engines like diesel engines.