I never really understood the emissions situation.  I was told that Duetz was pushed away from the air cooled engine by emission requirments, but previously I was also told that Duetz virtually owned the underground mining market because they were the only diesels which could meet the stringent emissions requirements. 

I never thought those two statements regarding the same engine made sense.  

I do know our Duetz tractor runs pretty clean compared to similar age Deeres, but it is no where near as clean as the new Perkins of similar size.   Even the newer small NH and Deere turbo engines don't seem nearly as clean as the late '90s Perkins 100- series engines.   This is my unscientific observation...basically based on how long you can have one running in the closed shop comfortably.  I think the Fastrac or telehanders could run for an hour and still be fine, compared to the 4010 or 4000 Deere that have you heading for the door a minute.   The TS110s or 6415 Deere will have your eyes burning in ten minutes or so.  I think the old D8006 is about comparable to them.