In a diesel engine the fuel used is:

Detailed Solution:

The correct answer is “diesel only”.

In a diesel engine, the fuel used is pure diesel. Diesel engines operate by compressing air to a high temperature, then injecting diesel fuel into the hot, compressed air, which ignites due to the high temperature.

In a petrol engine, the fuel used is a mixture of petrol (gasoline) and air. The mixture is drawn into the engine's cylinders, where it is ignited by a spark plug.