Why the diesel engine has better mileage than petrol engine?
A comparable total power (horsepower plus torque) diesel engine will go farther on a gallon of fuel for two reasons. First is that diesel fuel has more carbon in each gallon, which is what burns. That means it takes less of it to give the same explosive power in the cylinder, which is what drives the vehicle. Thus you get more work out of the same amount of fuel. Second, diesels have a much higher compression ratio than an Otto cycle spark-ignition engine. That means there is a greater expansion ratio involved in each explosion, again causing more power. Otto cycle spark-ignition engines cannot have that high a compression ratio because the gasoline/air mixture would explode from the heat generated before the piston reached the top of the compression stroke, and blow a hole in the cylinder wall or piston, break the piston rod, or blow the head gasket. Daimler-Benz has shown what they call a dies-otto engine that somehow combines the high compression of a diesel with the lower cost of g
