The question, “why do they use diesel in large vehicles rather than petrol?” is a good question. It is a good question because it implies another question, “why don’t they use petrol in large vehicles rather than diesel?” After all, petrol pollutes less than diesel. Right? Wrong, actually.
Irrelevant factoids cloud the question, “do diesel engines pollute more than petrol engines?” Gasoline engine manufacturers and oil refining companies would like to have you believe so, but it does not. Simply, the answer is, no, diesel engines do not pollute more than petrol engines. In fact,
Fuel efficiency is the product of two variables. Fuel density is one of two factors that determine fuel economy and thermal efficiency is the other. That is to say, fuel density and thermal efficiency determine the “gas” mileage of diesel, gasoline, biofuel, ethanol, and propane-powered vehicles