The ignition characteristics of diesel are expressed in terms ofa.Octane number b.Cetane numberc.Viscosity d. Flash and fire point

The ignition characteristics of diesel are expressed in terms of the Cetane number.

Here's why:

a. Octane number: This is used to rate gasoline's resistance to knocking or pinging during combustion. Diesel fuel doesn't ignite by spark as gasoline does, so the octane number isn't relevant for diesel.

b. Cetane number: This is a measure of the combustion quality of diesel fuel during compression ignition. A higher cetane number indicates that the fuel ignites more quickly when sprayed into hot compressed air. Therefore, the cetane number is the correct answer.

c. Viscosity: This is a measure of a fluid's resistance to flow. It affects the operation of diesel engines, but it doesn't directly express the ignition characteristics.

d. Flash and fire point: These are safety measures. The flash point is the lowest temperature at which the fuel can vaporize to form an ignitable mixture in air. The fire point is the temperature at which the vapor continues to burn after being ignited. They don't directly express the ignition characteristics of diesel.