Mazda is doing interesting work here combining the spark ignition and diesel ICE techs ... compress the fuel to almost the point of self ignition, inject a tad more into the vortex and ignite the center, creating a compression wave which ignites the rest of the fuel ... more power, more torque at lower rpm, improved efficiency.
https://spectrum.ieee.org/transportation/efficiency/mazdas-new-skyactivx-engine-gives-new-life-to-internal-combustion