According to an article in today's MIT Technology Review, a Texas company has whipped up an injection system that relies on supercritical gasoline to deliver a much higher combustion efficiency. Their test vehicle obtained 64 miles per gallon in highway driving, though there was no word on how much power was actually delivered by the engine.

Transonic Combustion says the setup, which can be used to control diesel engine fuel management as well, supports engine operations from stoichiometric to lean 80:1 air-to-fuel mixtures while cutting nitrous oxide emissions in half.

How does it work? Gasoline is treated with a catalyst for partial oxidation, then is heated and pressurized to reach a supercritical state. It sounds a bit like direct injection, but Transonic's high-pressure approach negates the need for a spark plug. 

The company says three automakers are evaluating the system, called TSCi, but don't look for it in your next Ford. Reliability is a big question mark, and plenty of NVH and emissions hurdles may have to be overcome. 

If there's no spark plug, then it *was* a diesel engine,  even if it ran on gasoline instead of diesel fuel.