Mechanical Engineering - Automobile Engineering - Discussion

The correct answer is it measures delay period. Now the reason is that knocking in engine is dependent on delay period. In order to avoid detonation or knocking in SI engine the delay period should be long.

But in CI engines the knocking happens before combustion (in SI-after (end) of combustion) the delay period the delay period should be less. If delay period is longer the fuel injected and accumulated in cylinder more and very high temp and pressure is generated inside cylinder.

So for CI engine alpha methyl naphthalene has very long delay while for cetane its very less. So given answer is correct.

The main difference between cetane and octane ratings is that the octane rating represents how well a fuel can resist pre-ignition due to compression"ensuring 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. In other words, it is how minimized the delay is between when the fuel is injected into the chamber and when the combustion begins.

Cetane number or CN is a measure of a fuel's ignition delay, the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. Cetane numbers are only used for the relatively light distillate diesel oils.

Cetane number or CN is an inverse function of a fuel's ignition delay and the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel.

In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower Cetane fuels.

So option D is the correct answer.

Cetane number is the function of a fuel's ignition delay and the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower Cetane fuels.

Cetane number is actually a measure of a fuel's ignition delay. This is the time period between the start of injection and start of combustion (ignition) of the fuel.

In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels.

D is the right answer. Cetane and octane number both measure the tendency of the fuel to ignite spontaneously. For diesel cetane number is 40-45.

For petrol octane number is 80-90.

If cetane number is low then ignition quality vl be poor and time delay will be high.

The resulting cetane number is then calculated by determining which mixture of cetane (hexadecane) and isocetane (2, 2, 4, 4, 6, 8, 8-heptamethylnonane) will result in the same ignition delay and another testing by ignition tester.

The correct answer is D, cetane number is used to measure the delay period in case of diesel engine but Cetane number and octane numbers are used to measure ignition quality in case of petrol (gasoline) engine.

Answer is right, cetane number indicates delay period of combustion in pressure condition. Higher cetane number gives higher compression ratio.