rbt
Senior Member
The industry has been using the term "clean diesel" for about the past 10 or 15 years or so, basically since the EPA began to seriously ratchet up the emissions regulations on diesel power.
Yeah, there are specific numbers associated with each generation and "generation" seems to specifically indicate which sets of targets the engine meets.
It's sufficient to say that gen 2 engines are cleaner than gen 1 (or gen 0) and gen 4 engines which is where we are heading are cleaner than what we get today.
The problem is "clean diesel" is a boolean but actual progress is a gradient. Using the milestones on the gradient is better for marketing purposes.
I would say todays diesel is clean but not clean enough to stop engine R&D.