ANS:A - ignition delay

The cetane number of a diesel fuel is a measure of its ignition quality. Here’s an explanation:

• Cetane Number: The cetane number (CN) is a measure of the ignition quality of diesel fuel during compression ignition (diesel) engines. It indicates how readily the fuel ignites when injected into the combustion chamber.
• Ignition Quality: A higher cetane number indicates that the diesel fuel ignites more readily under compression, leading to a shorter ignition delay period. This results in smoother combustion, reduced noise (knocking), and better overall engine performance.
• Impact on Engine Operation: Diesel engines operate more efficiently with fuels that have higher cetane numbers because they allow for more complete combustion, lower emissions of pollutants like particulate matter and unburned hydrocarbons, and improved fuel efficiency.
• Comparison to Octane Number: The cetane number for diesel is analogous to the octane number for gasoline, but they measure different qualities. While octane number measures the resistance to knocking in gasoline engines, cetane number measures the ease of ignition in diesel engines.