Mechanical Engineering - Automobile Engineering - Discussion

Guys, understand that self-ignition temperature measured at a Normal atmospheric pressure, in that case, diesel burn at 210°c whereas petrol at 280°c.

Due to low self-ignition temp, we can burn diesel without sparkplug at high compression ratio.

Given Answer is right. But the confusion is created due to the fact that we have seen petrol catching fire easily whereas diesel doesn't.

This is because of their chemical properties. Petrol having simpler formula and highly flammable /vapourable, gets atomised and sustains ignition (combustion) upon firing.

But diesel on the other hand, is heavier/viscous than petrol. This is therefore, in spite of having a lower self-ignition temperature it does catches fire earlier but can't sustain combustion.

How it is possible, otherwise why spark plug is used in petrol and not in diesel :P?

That is the same reason spark plugs are used in petrol because it needs higher temperature to ignite but in case of diesel higher compression (pressure) and lower temperature are enough to ignite it.

Diesel - 400 degree celsius, petrol - 280 degree.

Diesel 210 degree Celsius; petrol 245 - 280 degree Celsius.

No, Mr. Retheesh.

The self-ignition temperature of Diesel is higher than petrol. That is why we use a spark plug to ignite petrol engines and don't use external ignition source for diesel engines.

Absolutely wrong answer.

The answer is wrong because diesel needs higher compression ratio to get ignite, thats hy fuel injectors are used in place of the spark plug, petrol is a purified form og diesel only. So it ignites more quickly.

B is correct, I agree with @Retheesh.

Self-ignition temperature of petrol is 247-280°C. Self-ignition temperature of diesel is around 210°C.