Mazda’s SPCCI compression engine: Here’s how it works.
Homogeneous charge compression ignition (HCCI) engines combine a diesel’s torque and fuel efficiency with a gas engine’s cleaner emissions. The HCCI technique has been a goal of automakers since the hot-bulb compression engine was first prototyped in the late 1800s.
There have been many hurdles to jump, including getting the timing, temperature and mixture right, but Mazda thinks it has done just that with its new Skyactiv-X four cylinder.
http://autoweek.com/article/technology/7-things-you-need-know-about-mazdas-new-compression-engine