Im studdying PV diagrams for dieslel and petrol engines, and I've noticed that for Diesel the fuel is combusted at constant pressure as opposed to petrol (gasoline) which is at constant volume. I know that the area inbetween the lines is the net work done by the engine. So if you look at the graphs: http://img861.imageshack.us/img861/5465/pvdiagram.png [Broken] You can see that the shape of the petrol curve has a naturaly larger area than the shape of the diesel area. (Like a star shape has a naturaly larger perimeter than a square). The petrol curve has like a extra triangle of area over the diesel curve. Is this why diesels are generaly less powerfull than petrol engines?