The issue with ICEs is the fossil fuel part, not the engine part. Synthetic hydrocarbons and alcohols don't contribute to climate change at all. And alcohol fuels are both easy to make and about as good as hydrocarbons.
> Synthetic hydrocarbons and alcohols don't contribute to climate change at all.
If you are able to manufacture them in a completely emissionless way. That requires huge energy input though. Certainly has its uses, but too expensive for personal cars I'd think.
What I think would make sense is to use methanol as a seasonal energy store in temperate climates. Manufacture from PV in summer, burn in winter.
To be fair, DIY natural gas production from kitchen waste is a thing some people have done. It’s surprisingly doable and produces surprisingly large amount of usable energy.
Methanol is the obvious choice, because there are so many ways to make it. Shipping certainly looks to be moving in that direction, though ammonia is also being trialled. Ethanol via fermentation is also doable at scale, but most effective pathways rely on using arable land.
If we're talking synthetic fuels, you'd probably run cars on methanol rather than a hydrocarbon. Planes absolutely need kerosene, but cars can claw back most of the performance of petrol with alcohol fuels, and methanol is the simplest and cheapest to make. Certainly shipping seems to be going this way.
