Correct Answer - Option 2 : Kerosene
Cetane Number (CN):
- It is the most important single fuel property which affects the exhaust emissions, noise and start-ability of a diesel engine. In general, lower the cetane number higher are the hydrocarbon emissions and noise levels. Low cetane fuels increase ignition delay so that start of combustion is near to top dead centre.
- The cetane number of a diesel fuel is a measure of its ignition quality.
- Though ignition delay is affected by several engine design parameters such as compression ratio, injection rate, injection time inlet air temperature, it is also dependent on the hydrocarbon composition of the fuel and to some extent on its volatility characteristic.
- The cetane number is a numerical measure of the influence the diesel fuel has in determining ignition delay. Higher the cetane rating of the fuel lesser is the propensity for diesel knock.
- For higher speed engines the cetane number required is 50, for medium-speed engine about 40, and for slow-speed engines about 30.
Petrol has zero cetane number.
Alcohol has approximately 12 cetane number, so modification is required to use it.
Ammonia has a low cetane number and low flame speed makes it difficult to apply in combustion engines without modifications.
- Kerosene cetane number lies between 30 - 40
Lower speed engines likely will do better on kerosene than modern high-speed automotive engines in part because historically diesel fuel specifications called for far lower cetane and so kerosene is closer to meeting the design specifications for such engines without modification.