Quote:
Originally Posted by ERTW
1. running stratified charge is how diesels manage to run ultra lean. This improves economy and soot emissions. running homogeneous mix would defeat this.
2. because of the high compression ratio, the valves need to be opened/closed so that they don't hit the piston. This increases pumping loss. So a turbo IS needed to overcome this. Removing the turbo will hurt economy AND power.
3. It's the high compression ratio and lean running that leads to NOx.
So your suggestion is to make a 40%+ efficiency diesel run like a 33% efficient gasoline engine?! 
To make the *engine* more efficient, which is the original intent of the OP, you can reduce pumping losses further by porting, back cut on the valves, and a good valve job. Late intake valve closing will further reduce pumping losses, as well as kill a little power i.e. a bigger intake cam. Kind of a Miller cycle diesel  |
ERTW good points on the last paragraph there. I will have to look into the Miller cycle a bit further.