There is some interesting technical discussions here. Basically it comes down to some NOx storage and conversion that doesn't use urea, some fancy EGR work, and cylinder by cylinder combustion balancing. FWIW, the upcoming Mazda oil-burner uses relatively low (for diesel) compression ratio of 14:1 to limit peak cylinder pressures. This keeps NOx down and means no urea system. Matt
I can see a few advantages and disadvantages in dropping the compression ration as Mazda has done - like harder starting in cold weather - bigger, more powerful glow plugs or carrying "starter" fuel, like a gasoline mix or something, lower specific HP and torque outputs, less fuel economy for the size of the engine and so on, on the plus side is a quieter engine, less NVH to deal with and lighter construction, plus the easier emissions situation. Interesting article, and the part I liked reading was that there's still a lot more performance in the VW engine to come, thru further tweaking of the systems already in place.
There are amazing things coming... I read some of the SAE stuff on what's coming for engine management. You are just starting to see combustion chamber diagnostics via monitoring of spark plug current and voltage waveforms, like the glow-plug stuff that they mention here. While this is good for specific output and efficiency, it will be a royal pain for the tuner community. Some of the stuff that is in the works is using real time feedback to control that very combustion cycle, not just the next one coming. It's really amazing, that's for sure. Anyway, I posted this up so that those that wonder why BMW doesn't bring thier diesel here can see some of what goes into it. BMW has some BS answers, like there is no room for urea, when it's kind of obvious that BMW just hasn't done a urea-less system! While Mazda is skinning that cat with a different knife, that will be two manufacturers that have figured out how to do a decent small diesel for the US market that doesn't require the urea system. And as the new regs kick in in Europe, they'll either have to figure out how to skin that cat or give up on diesels in small cars, something I don't think they want to do. Going a bit off topic, we do get some BS answers from corporate. When Jim McDowell was asked about MINIes his answer was something like: Well, it sure was a nice test bed but we didn't see it as a winner because you really need a rear seat..... While this is true as far as it goes, it totally ignores the company that does MINI electric conversions and keeps the rear seat! Anyway, I always find it interesting to see what tech comes from the different players.... Matt
Did you see the take rate on the Jetta Wagens? 80%!! I think it's at the point where people buy a VW for the diesel engine. I think buyers gravitate towards the MINI first, then pick an engine, not the other way around.