Petrol burns at far less temperatures than diesel so requires less compression and a simple spark to ignite it and because of the lower compression can reach far higher revs than diesel, while diesel engines are more powerful at lower revs because of the excessively high compression required to ignite the diesel fuel (if you compress air it cerate's high temperatures) so you have two different engines for different types of vehicles (although diesel's have improved immensely in the last 15 years)*****
Wankel Rotary Engines are not as reliable as conventional engines they don't last nearly as long so there efficiency is negligible comparison.