Given that the traditional four-stroke Otto-cycle engine piston engine only has a thermal efficiency of 25-30 percent, there is clearly still plenty of room for improvement. While most of the green automobile attention in recent years has been focused on electrification, liquid fuels still have about 100 times the energy density of today's best lithium-ion batteries, a difference that probably won't change significantly any time in the near future.
Generally speaking, we don't like the idea of being Supercritical. Being critical is bad enough without super-ing it, right? Apparently, though, being Supercritical with fuel is a good thing, as a company called Transonic is reporting that it has managed to boost the efficiency of an internal combustion engine in its testing by 50 to 75 percent.