Mechanical Engineering - IC Engines and Nuclear Power Plants - Discussion

Auto-ignition temperature of Gasoline (petrol) is high as compared to Diesel. And spark plug is used because we can't compress air within the cylinder about 250° Celsius.

Auto-ignition temperature of Gasoline (petrol) is high as compared to Diesel that's the reason of using spark plug in the Gasoline Engine. If it is not then we don't use to spark plug in Gasoline Engines.

Self-ignition temperature of petrol is higher as compared to diesel. This is the reason we need the spark to ignite the charge (petrol).

I think B is the right answer.

In a petrol engine, it is imperative that the autoignition temperature (the temperature at which the fuel will ignite itself) of the fuel stays high enough.

Because, if it is very low, then as the mixture is being compressed, it will ignite itself as soon as its auto-ignition temperature is reached. This ignition may happen even before the spark plug shoots a spark.

This phenomenon is called auto-ignition and results in engine knocking (a very distinct metallic knocking sound).

The calorific value of petrol is greater than diesel engine so that pre ignition temp of petrol is less than diesel.

According to above data B should be right answer.

Substance
Autoignition point (°C)

Butane
405 °C

Carbon disulfide
90 °C

Diesel or Jet A-1
210 °C

Diethyl ether
160 °C

Ethanol
363 °C

Gasoline (Petrol)
247-280 °C

Hydrogen
536 °C

Magnesium
473 °C

Paper
218-246 °C

Silane
21 °C

Triethylborane
-20 °C

White phosphorus
34 °C

Auto-ignition temperature of fuel :

Diesel=210 degree.

Petrol=246 degree.

Self ignition temperature is that temperature at which fuel starts burning without any assistance as flame or burner. And we also know that the calorific value of petrol is more than the diesel, and will easily burn compared to diesel hence we can say that the self ignition temperature of petrol is less than the diesel.