It's not a slab of lard sitting in the gas tank. It's processed and blended with other compounds. Remember Jura all fossil fuels were at one time Organic fats.
That's what Hydrocarbons are an Organic means of storing energy most of it being based on the remains of primitive swamp plant life from before the age of the Dinosaurs.
Is It green? Green is kinda a buzz word really is it avalible form a reliable supply? Yes yes it is. Biomass happens every where and biofuels like biodiesel can be sourced from any where even your local golden arches.
Is it Clean? well It tends to burn slightly cleaner then the conventional fuels. this is as it's more tailored a mix as you don't have extra compounds mixed in because it's blended by man vs by whatever happened to have formed underground.
Is it an alternative? on sourcing yes.
better warfighting. because the fuels are blended the way they are. they are basically tailored to be richer in Octane then conventional fuels with less contaminates this means that the fuel has more bang for it's weight then the same conventional fuel which is where the weight comes in for any platform a fuel with less inclusive compounds operating in a combustion system is going to burn cleaner and better giving better results especially in the case of a weight critical platform like a navy ship or aircraft.
Consider the Royal Navy's change from Coal to Oil fire.
Prior to 1890 from the start of the steamer ship, Coal was the established fuel for the navy, It was safe to handle and widely available. yet It couldn't be transferred at sea, exhausted a crew refueling and was nasty to those handling it from miner to salor. It produced the thick toxic smoke visible for miles.
Oil however offered a fuel that was more volatile , yet Oil burns hotter meaning smaller lighter boilers allowing increased range. Oil could be pumped meaning that fueling at sea could be done and the whole crew was not needed to shovel rocks It cut the crews down by not needed crews to continually shovel coal. All of which increased the range and speed of the ships and created less smoke.
If these new fuels perform as advertized in the end who cares what it's made from.