ICE aren’t growing much in size and are getting more and more efficient. Why not make them air cooled? Porches used to be aircooled, and those were performance cars with the engine in the back. I would imagine having an engine in the front might be easier to cool, no?
All those methods start with biomass, don’t they?
The issue with biomass is that it eats into food production and nature. (It is also not climate-neutral, if fertilizers from fossil sources are used.) Burning it is also not emission free (regardless of production), which will become a problem in countries or regions that are going to mandate “zero emission” for new vehicles by a certain date. Upcoming emission regulations, like Euro 7, even regulate emissions (dust) caused by brakes or tyres …
Other types of synthetic fuels also exist, but most of them also use biomass as their source or share their main problem with hydrogen: They need huge amounts of electricity for production, which means we would need much more renewable energy (some sources claim 3 to 5 times as much as charging a battery directly) to power the same amount of vehicles.
Considering there are already ongoing protests against renewable energy sites (they supposedly disturb the natural beauty, etc.), I think it is highly unlikely that the general public will support even more renewables. Even more importantly, the fuel will be significantly more expensive to purchase than simply charging a battery, due to its production and transportation costs.
I don’t think that those technologies will be available at affordable price points in the foreseeable future. The general public will most likely adopt the most well-established, economical and practical “zero emissions” technology on the market, which at the moment appears to be the battery-electric car.
In other areas (airspace, shipping, etc.) we might see the adoption of synthetic fuels or hydrogen, but I don’t expect it to be cost-effective for regular passenger cars anytime soon. If synthetic fuels ever become available in passenger cars, they will, in my opinion, most likely be exclusive to low production models (e. g. Porsche e-fuel production, etc.) and therefore only be available to rich people.