I have heard bad things about diesel cleaners. My thinking is that if it was a good additive, the fuel people would have added it already and if it isn't, why add it.
Like I said earlier, things down here are different, but I only run the 50 ppm low sulphur fuel. Its only been available for about a year here, but it makes a difference. There are people with more knowledge on the internet, so google is your friend.
The owners manual does say something about a particle filter in the exhaust system, and that driving at 80 kph for 20 minutes will burn it clean. I assume its the same for the cat. I think the fine black particles you refer to is soot from unburned fuel. The diesel engines don't like running high revs, and anything above 3000, on the Renault k9k engine in the Micra, it starts wasting fuel out the exhaust. If its white smoke, its oil, and you have a big problem.
It gets real technical, but Diesel is a slow burning fuel, and the fuel does not get a chance to completely combust before the exhaust valve opens. I used to drive tractors on a farm for a really cranky old man, and he used to slap me on the side of the head if the exhaust starts belching black smoke. I had the wrong throttle setting, or gear, or anything really. I didn't stay there long, but I did learn a healthy respect for my throttle settings.
The fuel filter only needs to be replaced every 5th service or something like that. But now that I think about it, mine hasn't been changed in 2 years, so guess what I am doing the weekend?
