I think it depends a lot on compression -- "typical" american diesel engines tend to run very low compression by diesel standards, used to be 16:1 or 18:1, with direct injection and fixed injection timing. Not always true, please don't start a flame war!

European (MB, Peugout, VW/Audi/Volvo) practice has been much higher compression ratio (21:1 on the 61x engines, 22:1 on the 60x, I think, 23:1 (and actually as high as 26:1 in manufacture) on the VW/Audi). This results in much better combustion, along with the use of prechambers of some sort and high swirl heads.

American diesel design was essentially stagnant for many years -- the basic engine designs weren't upgraded significantly, at least for the automotive/truck applications, until the middle 90's when the EPA started applying pressure due to the carcongenic nature to the inky black soot from the low compression, fixed injection timing engines. We've all seen and old Mack or Detroit blowing huge clouds of smoke on each gear change.....

That said, fuel quality also has a lot to do with carbon accumulation, and American #2 diesel is both rather low grade by international standards, and highly variable.

Use of a diesel treatment like RedLine will help reduce soot accumulation, but the best thing is to find a fuel that doesn't smoke.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!