Are there any special kinds of fuels that manufacturers are considering in order to make high performance, high efficiency jet 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.