[themitigating]

Synthetic fuels are potentially valuable because they allow existing capital assets (internal combustion engines and the industry that produces them, fuel distribution infrastructure) to continue to be used.

Won't engines have to be modified and reprogrammed?

[Oxidation]

According to this article: maybe not, since they used an unmodified engine.

[PaulHoule]

For alcohol, DME and other single entity fuels you may need to change the engine, but synthetic hydrocarbons really are a drop in replacement.

[jacquesm]

Most engines that run on gasoline will run unmodified on LNG and many other combustibles besides, alcohol would work but the way in which it and ethanol attack various materials found in the fuel systems of vehicles means that your problem is likely not going to be the engine but further upstream towards the tank (seals, membranes).