The word revolutionary has been thrown around so often that it’s lost its edge, but the Mazda SKYACTIV-X engine earns it. It’s the world’s first production gasoline engine to pull off compression ignition, a combustion method engineers have been chasing for decades.
Exploring Mazda SKYACTIV-X Engine Technology
Benefits of Compression Ignition
A compression ignition gas engine targets the holy grail: diesel-level efficiency with gasoline’s smooth, high-revving character. Mazda’s SKYACTIV-X gets the closest to this ideal engine by improving the seven key factors important to efficiency: compression ratio, specific heat ratio, combustion period and timing, heat transfer, intake-exhaust pressure difference, and mechanical pressure.
For instance, while SKYACTIV-G allowed for a 13:1 compression ratio (well above the typical 8:1 to 12:1 found in most gas engines), SKYACTIV-X pushes up to 16:1, a level once considered off-limits for gasoline.
How This Engine Works
The core of SKYACTIV-X is a system called Spark Controlled Compression Ignition (SPCCI). The process begins with an ultra-lean air-fuel mixture, much leaner than the typical 14.7 to 1 ratio. During the intake stroke, this mixture enters the cylinder and is swirled by a baffle, which pushes the air-fuel mix along the cylinder walls.
As the piston climbs, compression heats the mixture. Just before spontaneous ignition, a second shot of fuel is injected near the spark plug. This rich pocket, about 29:1, is ignited by the spark plug. The resulting flame doesn’t ignite the rest directly. Instead, it spikes cylinder pressure, causing the surrounding ultra-lean mixture to ignite all at once through combustion.
There’s a Supercharger
Another crucial piece of SKYACTIV-X is a small, belt-driven Roots-type supercharger that pushes up to 7 psi of boost. This device increases airflow rather than horsepower, ensuring the engine gets enough air to maintain the lean mixture needed for efficient combustion. It’s clutched, so it disconnects at low speeds to prevent the air-fuel mixture from getting too lean.
Real-World Impact
1. Better Fuel Economy
Mazda’s 2.0-liter SKYACTIV-X can match or even beat the fuel efficiency of their 2.2-liter SKYACTIV-D diesel. That means it’s about 20 to 30 percent more efficient than the regular 2.0-liter SKYACTIV-G gas engine.
2. Improved Output and Responsiveness
The SPCCI tech in the 2.0-liter straight-four engine cranks out about 190 horsepower and 207 pound-feet of torque. That’s a nice bump over the Mazda 3’s 2.0-liter SKYACTIV-G, which only puts out 155 horsepower and 150 pound-feet. Plus, since the throttle valve stays open most of the time, the engine delivers a quicker initial acceleration, kind of like a diesel, which doesn’t have a throttle valve at all.
For more information on SKYACTIV-X or the other amazing technologies Mazda has up its sleeves, swing by Tom Bush Mazda in Jacksonville, FL.
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