Automakers like BMW and Porsche are investigating synthetic fuels as a way to keep internal-combustion engines alive in the face of stricter emissions standards. But Engineering Explained host Jason Fenske is skeptical of this new fuel technology.
While gasoline and diesel are refined from naturally occurring stocks of crude oil, synthetic fuels are made by combining different molecules into a substance that performs like a conventional fossil fuel in a combustion engine.
That process is supposed to be carbon neutral, because one component of most synthetic fuels is carbon extracted from the atmosphere, Fenske noted. So while burning synthetic fuel may still produce carbon emissions, they would theoretically be canceled out by the recovery of that carbon for more fuel production. Plus, unlike fossil fuels, you can always make more synthetic fuel.
In addition to keeping gasoline cars on the road, synthetic fuel also has one of gasoline's main advantages—energy density. It can't match gasoline for energy density, but it's much better than hydrogen or the lithium-ion batteries used in current electric cars, Fenske said.
Artist's impression of Haru Oni synthetic fuel pilot plant
However, synthetic fuel must be made using renewable energy in order to be cleaner than gasoline, Fenske said. That's not true of electric cars, which can still have a very small carbon footprint even when charged from the dirtiest electricity grids.
Charging an electric car is also a fairly straightforward process, whereas making synthetic fuel, transporting it, and then burning it in a combustion engine adds a lot more steps, making it inherently less efficient.
Consequently, less of the energy put into synthetic fuel actually makes it to the wheels, Fenske said, citing some recent studies. Synthetic fuels' greater energy density might make them a good fit for aviation or maritime applications, but even that would still be very expensive, Fenske concluded.
Those challenges haven't discouraged automakers from experimenting with synthetic fuels. Porsche is testing it in race cars, and is backing a pilot plant in Chile. Last year, BMW invested in Prometheus Fuels, claiming the startup would be able to sell synthetic fuel at a price comparable to gasoline.