Why are DI cars dirty?

[BMWTurboDzl]

I swore I remembered reading about it awhile ago and remembered being on a website where it talked about such a program and the details of it. I can't seem to find it now though. Who knows. Maybe it was a dream.

Initially when problems with the M57 (335d US model) started to crop up BMW was unable to perform a walnut blast due to the curvature of the intake runners inside the head. Consequently BMW would have to send the head out for cleaning. Talk about big $$ on warranty costs.

Perhaps that's why you're thinking of a head exchange?

 

[PandaBear]

GDI can be cleaner if you burn lean, it was not new around the world but only "new" to the US emission standard. They were around since the 90s and they were burnt much leaner, producing more NOX so they would fail the US emission (California).

To make it pass the California emission they have to burn richer, thus reducing NOX but increase the soot, plus the carbon deposit on the intake valve if they are not designed right (keeping the valve hot), or uses dual injection.

There is no way forward to meet CAFE cheap without direct injection, so it will be around, but it may get better with dual injection like Toyota did to some of their newer engines, or go hybrid and stay port injection using pseudo-Atkinson cycle.

That's the same reason Skyactiv-X is not in the US, they would have a lot of emission issues with HCCI burning leaner, even worse than GDI, so they would fail NOX and / or soot.