[thescriptkiddie]

It's not exactly the same as a diesel engine. Diesels use a stratified charge (SCCI), meaning fuel is injected at the end of the compression stroke and burns immediately, without having a chance to mix thoroughly with the air. This engine uses a homogeneous charge (HCCI), meaning fuel is injected at the beginning of the intake stroke but does not ignite until the end of the compression stroke, therefore having time to mix with the air. This subtle difference makes the engine much harder to control, but should yield lower NOx and particulate emissions as well as higher power output.

Also, the engine is capable of running in HCCI mode under light-ish load. It still has spark plugs, and can run as a normal gasoline engine (HCSI) when high power is demanded.