Is there a special kind of fuel needed to obtain high efficiency engines?
Surprisingly, it isn't a big factor in GA or commercial aviation.

                            Specific  Energy
                            Energy    Density
                            MJ/Kg     MJ/L
Diesel / Fuel oil           48        35.8
LPG (inc Propane / Butane)  46.4      26    
Jet fuel (Kerosene)         46        37.4
Gasoline (petrol)           46.4      34.2
HMX (Rocket Fuel)            5.7      10.8  


Even high-performance long-range military aircraft like the U2 and SR-71 use some variant of Kerosene with additives, their fuels are optimized for high flash point, not for energy density or for specific energy.

Generally, availability and infrastructure trump efficiency.


Wikipedia: Energy Density
Aircraft Diesel Engine