First, a very precise direct-injection system operates at much higher pressures than customary for a gasoline engine: 200 bar, or about 2,900 pounds per square inch.
This isn’t as high as the most recent diesel engines, at up to 2,200 bar or 32,000 psi, but it allows the fuel to be precisely injected into the right place below the spark plug despite the high compression ratio.
Second, an air compressor—Mazda goes to great lengths not to call it a supercharger—packs more air into the cylinder to keep the main air-fuel mixture sufficiently lean.
Finally, and most important, sensors in each cylinder and the most powerful engine-control processor Mazda has ever fitted allow real-time adjustment of the air-fuel mix and spark timing for each successive combustion event.
Previously, a 4-cylinder engine would be adjusted after all four cylinders had fired once. Now, the mix in each individual cylinder can be adjusted on the fly to ensure maximum efficiency depending on the operating demands.
Mazda SkyActiv-X engine: three changes to hardware and sensor ancillary equipmentEnlarge Photo
That’s something Mazda couldn’t have done until very recently: When the company’s development engineers had tried it with a 2012-vintage SkyActiv-G engine, the engine control unit simply froze under the computational load.
Powerful processors required
Only with half a decade’s advance in computing power could the necessary precision be achieved to adjust each combustion event in real time.
The engines we drove had a handful of rough spots in their software mapping, producing the occasional stumble or rough transition among engine speeds and gears.
But the results, taken directly from data loggers wired to the test cars' control systems, were impressive.
2020 Mazda 3 prototypeEnlarge Photo
Mazda SkyActiv-X engine results, 2020 Mazda 3 development prototoype, 6-speed automatic transmissionEnlarge Photo
Mazda SkyActiv-X engine results, 2020 Mazda 3 development prototoype, 6-speed manual gearboxEnlarge Photo
Of the two prototype 2020 Mazda 3 development cars we drove, the six-speed manual version delivered 34.6 mpg and the one with Mazda's six-speed automatic transmission returned 39.9 mpg.
Some of the drive cycle was standard traffic around suburban Frankfurt, including low-speed residential and town stop-and-go, but we also spent a few miles at up to 160 km/h (100 mph) during two short stints on the autobahn.
More interesting yet, the output from the data loggers showed that the engines in both cars spent more than 90 percent of their time in HCCI mode.
If these test results translate into production cars, Mazda will be able to offer a SkyActiv-X engine that's only somewhat more expensive than its current 2.0-liter model with far better fuel efficiency.
A reduction in carbon emissions and running costs of up to 20 percent is rarely found in new vehicles, much less with an engine that adds only an air pump, high-pressure fuel injectors, and in-cylinder sensors.
Mazda provided airfare, lodging, and meals to enable High Gear Media to bring you this first-person drive report.