Mazda will debut its new Skyactiv-X engine technology in a few weeks, but it's already testing the compression-ignition drivetrain on the road—and it wants you to know about it. Spy photographers have spotted Mazda3 prototypes wearing very conspicuous Skyactiv-X graphics.

The test mule seen in these photos appears to be a pre-refresh Mazda3, but what's most interesting about it is the prominent "Skyactiv-X" script scrawled along the doors. There's also a large "5" toward the rear fender, a likely sign there are more prototypes out there. There's a good chance that under the current Mazda3 sheetmetal lies the bones of the next-gen model, as Skyactiv-X tech is said to debut with the new Mazda3.

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As we previously reported, Skyactiv-X uses a combination of spark and compression ignition to improve fuel efficiency and reduce emissions. A supercharger is also used to increase torque. Mazda didn't give details like cylinder count, but we expect the next Mazda3 to again be powered by a four-cylinder. Eventually, though, Mazda plans to start electrifying its lineup in certain regions, so we could see a hybrid or all-electric version of the compact by 2019.

Mazda is set to debut its Skyactiv-X engine tech at the Frankfurt Motor Show this month, when we'll hopefully learn a few new details about the next-gen Mazda3. In the meantime, check out the spy shots of this mule and imagine the diesel-like sound of its engine.