The differences between gasoline and diesel engines lie not only in their fuels, but in how those fuels are ignited.
Gasoline engines use spark plugs, while diesels simply use compression.
But it is possible to ignite gasoline in an internal-combustion engine with compression, as in a diesel.
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The process is known as homogeneous-charge compression ignition (HCCI), and it's a technology multiple automakers have experimented with over the years—but never put into practice in production vehicles.
That may be about to change though.
Mazda is one of two automakers planning to introduce a homogeneous-charge compression engine next year, and expects a 30-percent improvement in fuel economy over a conventional gasoline engine, according to Nikkei Asian Review.
2017 Mazda 3
The new engine will debut in the Mazda 3 compact as part of a mid-cycle refresh of that car, although it is unclear whether it will be available in all markets.
It will be considered part of the next-generation Skyactiv family of efficiency-focused engines.
Following its launch the Mazda 3, the homogeneous-charge compression engine may find its way into other models as well, according to Nikkei.
Automakers have investigated homogeneous-charge compression as a way to gain more efficient combustion, and to squeeze more power out of smaller-displacement engines.
General Motors, Mercedes-Benz, and Volkswagen have all experimented with the technology, but Mazda could be the first automaker to use it in a production car.
Infiniti will launch an engine with variable compression ratios—from 8:1 to 14:1—into which it hopes to incorporate HCCI down the road.
2007 Mercedes-Benz F700 Concept
The compression-ignition gasoline engine technology was demonstrated on the Mercedes-Benz F700 concept, which debuted back in 2007 at the Frankfurt Motor Show.
At the time, Mercedes claimed HCCI—along with other efficiency-related technologies—allowed the F700's 1.8-liter twin-turbocharged 4-cylinder engine to offer the performance of a 3.5-liter V-6.
GM tested Opel prototypes with HCCI engines around the same time, but has never indicated that the engines have gone beyond the research stage.
MORE: Food For Thought: Mercedes-Benz F700 Concept (Feb 2009)
These engines were criticized for being noisy and rough, something often said about the diesel engines whose ignition process they adopt.
Mazda's decision to adopt HCCI is part of a trend of automakers resorting to ever-more-complex solutions for achieving efficiency gains in the face of stricter global fuel-economy standards.
While it plans to launch an electric car in 2019, Mazda still believes internal-combustion cars will make up the majority of its business in the near future—so it will continue trying to find ways to improve their fuel economy.
[hat tip: Max Looker]