I'm not an expert on emissions, or what constitutes clean exhaust compared to dirty exhaust. I fail to see the logic in taking a diesel engine (SS60, DDEC III) that could deliver 8.0 MPG in our buses and in the process of making the exhaust cleaner (SS60 DDEC IV and above)make it burn more diesel.
In 1968 or thereabouts cars were forced to meet emission standards and it is only in the last decade that we are seeing not only clean engines, but engines with more power despite getting fantastic mileage and long life. During that 30 year time frame between when the standards were introduced and the real start of clean engines with real power our cars were strangled with air pumps and all sorts of interim measures that robbed power and increased fuel consumption.
I think the single greatest technological change that made our engines what they are today is the widespread use of very sophisticated computerization that can literally deliver the correct fuel/air mixture on every compbustion stroke.
I don't doubt diesels can make the same progress, but I think what we are seeing today is the repeat of the early emissions gas powered engines where add on features are required to meet the standards. Maybe 10 or 20 years from now diesel engines will meet the standards without any external devices or power robbing controls, but until we get there I think we have seen the last of good mileage and relative simplicity in the engines. I just wonder how truckers are going to impact what is happening. Right now truckers have access to all sorts of program mods for DDEC to give substantial power increases and unless and until the current crop of engines is built so they cannot be modified I think we can expect to see owners start modifying their engines. In the 90's a lot of Prevost owners were bumping up the HP in their 8V92 engines and we may be seeing a repeat of that.
But in the meantime I am going to try to figure out how less MPG equals good. It must be the tree huggers have one set of needs and they are in confict with those who want energy independence. The tree huggers won this round.