I'm disappointed that when it comes to diesels, most people in this forum seem to bury their head in the sands and resort to typical hardcore petrolhead dark ages crap. I'm surprised that so many here still equate diesel with black smoke.
This unfortunately unjustified black smoky diesel mentality is so prevalent thanks again to our world of mindless captalism. I bet most of you get your diesel impressions from 18 wheelers smoking like mad. The horrible truth is that environmental concerns always take a back seat to corporate bottom lines. If it wasn't for the new diesel emmsion laws in the US, no one would bother to upgrade their HD diesel truck engines to current levels of emmsion control.
Diesel always dirtier than petrol? You guys must be stuck in the 80's. My 1994 2.5L NA diesel Pajero (4D56) which emits NO visible smoke after a 1 minute warmup. It doesn't even have ANY of the modern emmisions control systems such as soot filters! I actually pushed it to its (4700rpm) redline on each shift just to test it, and guess what? No detectable smoke. It was performed under load, with someone at the back to observe the exhaust emmisons (don't try this yoursleves folks!) whilst on the move. Tests at no load (static car) again yielded no visible smoke. All done with traditional indirect injection (no common rail or other late tech).
When was the last time you see a well-maintained 2006 3.2L turbodiesel Pajero emit any visible emmsions? Bet none. The truth is, diesel is superior to petrol in all emmisions except NOx. That is simply a result of high air to fuel ratios, since our air is over 70% N2 after all. Robust (sulfur tolerant) NOx scrubbers already exist, so that will soon be a VERY moot point.
Petrols have always traditionally had problems with unburnt hydrocabons. If you read my posts from the diesel thread, you should understand why this is. The only way to generate significant unburnt diesel from a diesel engine is to significantly over fuel it or with poor fuel atomization. Petrols are always run at least slightly rich, and at any throttle setting below WOT, it only runs richer. And I have a hard time believing petrol emmsions don't have any carcinogenic effects too.
For the truely environmentally concerned, do remember that the AUDI R10 is still the QUIETEST race engine in recent history. Diesel turbo synergy... There is no substitute.
Unless people (especially americans) stop loosing their unfounded stigma of diesels, our energy, economic and environmental problems will only grow worse as we enslave ourselves to petroleum only gasoline. Although clean electric generation would be the ultimate solution, that is still too far fetched. Currently, diesels are one of the still relatively underdeveloped IC engines that still possese massive potential.
Speaking of black oils, that's pretty much standard practice these days for all kinds of engines, though its just more obvious for diesels. Today's detergent oils are designed to clean and suspend residual soot, and since the standard diesel oil change interval specification has grown form the old 5000km standard to the more recent 10,000km standard, this only gets more obvious. Contrary to poular belief, colour alone is a poor indicator of oil viality (except for extreme cases). The darkening oil doesn't mean that your engine's extra dirty. It simply means that the oil is doing its job.
If biodiesel production technology is allowed to develop full blast, we won't be complaining about petrol prices now. With reason biotechnological discoveries, the effeciency of biodiesel generation will only go up. Then again, we've got crude oil companies watching us. A recently discovered method to "grow" biodiesel via the use of specilalized algea had a oil production to area of land ratio than any of the standard contemporary source (canola oil, soy oil, peanut oil, plam oil, etc). Anyway, it's via photosynthesis, so a large portion of the CO2 emmitted from your biodiesel engines go right back to new oils. The circle of biodisesel life. A beautiful fusion of biological and technological solutions.
We must agree that petrols are facing obsolescence. It's about time we let technology progress and give a chance to potentially superior alternatives.