Earlier this month, Japanese automaker Mazda laid out its future powertrain strategy and dropped a massive announcement in the process.

In 2019, Mazda will introduce a gasoline-powered Homogeneous Charge Compression Ignition engine, dubbed Skyactiv-X, that the automaker promises will offer huge strides in efficiency and fuel economy.

That means tailpipe emissions are expected to be correspondingly reduced with the introduction of the new internal-combustion engine technology.

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HCCI has never been applied to mass-production gasoline-powered engines. It essentially lets a gasoline engine behave like a diesel under certain circumstances.

For a deep dive into how the technology actually works, Engineering Explained has tackled Mazda's upcoming Skyactiv-X engine and explained how the automaker expects to fulfill its promise of cleaner-burning gasoline engines.

It all starts with the HCCI technology itself, which compresses an air and fuel mixture until it self-ignites: no spark needed.


2018 Mazda3

2018 Mazda3

Specific temperatures are needed to ignite the mixture by itself, but this is also where earlier attempts at gasoline-powered HCCI engines have failed: ambient temperatures are critical.

Should the outside temperatures be too hot or too cold, it wreaks havoc on the HCCI process: temperatures that are too high create engine knock, while those that are too cold can hurt the ignition system itself.

So, Mazda has blended HCCI with current technology to remedy the problem: a spark plug was brought into the design.

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Mazda hasn't completely described how the engine will operate, but Engineering Explained makes some educated inferences.

When ambient temperatures are too low, or the engine is started after a cold soak, or it's operating at temperatures too high for the HCCI technology, a spark plug is used to ensure combustion occurs at the right time.


2018 Mazda3

2018 Mazda3

At the times when the cylinder temperature is conducive to compression ignition, HCCI takes over.

The leaner air-and-fuel mixture that can then be used reduces the total heat energy lost, which in turn lowers emissions.

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Mazda claims its SkyActiv-X engine will be 20 to 30 percent more efficient than its current generation of Skyactiv engines, which are often among the most efficient in any given vehicle segment.

It's unclear where the first Skyactiv-X engine will show up, but the redesigned Mazda 3 seems as though it could be a logical recipient.


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