Both gasoline and diesel direct-injection engines rely on two new processes.
One is injecting mixed fuel and air directly into each cylinder instead of into the manifold outside the intake valve. Direct injection improves the swirling motion to focus fresh fuel near the ignition source.
The other greatly increases the pressure under which fuel and air are mixed and injected into the cylinders. Higher pressure allows the fuel mixture to be sprayed in a finer mist for hotter and cleaner burning.