
The Mazda SkyActiv engine is a gas direct injection engine, meaning that the gasoline is fired directly into the combustion chamber. Direct injection engines generally fire the gasoline in a single stream, but the Mazda engineers designed the SkyActiv engine to fire multiple streams which allows for better mixture with the air, a cooler engine, and it helps set the stage for higher compression ratios. 
The Mazda engineers also redesigned the SkyActiv piston. The new piston is shapped somewhat like a volcano as opposed to the traditional cylindrical piston shape. This shape allows for a decrease in heat, increased compression ratios without the fear of uncontrolled combustion aka "knocking". In addition to this redesign the engineers decreased the engine weight and friction. 
