This could be one of my last posts on this topic, but i've found something interesting. Read on.... !
That's why with the whole assembly removed, the emission, other than soot are much the same.
I know I'm a bit long in the tooth, so just going straight to the point - when was that ever tested ?
Emmissions tests don't even form part of any diesel car MOT test. Yet
So did somebody take this engine, with the same CAT+DPF fitted, and even though it wasn't required they decided to test emmissions before and after removal of the CAT+DPF ?
What I know is that modern diesels only put out about <10% of soot of what they did even just 20 years ago. CO is in the ballpark of 0.05% of exhaust gasses, when a petrol was often 1-2% CO(without a cat) and sulphur dioxide is less for diesel than a petrol too.
If someone has actually done before and after tests then we just need that data to show what the effect is of removing the CAT+DPF assembly to see it for real. What equipment did they use ? Current exhaust gas analyser standards aren't good enough for a garage EGA to detect such small differences.
I think because of the fact that the CO emmissions from a diesel without a CAT are lower then a petrol engine with a CAT, that it is something of a non-issue at the moment to remove the DOC.
However, if CO testing did come along, exhaust gas analysers would need to be improved. The VOSA specification for an exhaust gas analyser, EGA, demands an accuracy of 3% rel. That isn't quite accurate enough to measure differences in diesel engine CO emmissions
Shows that calibration of an EGA is done regularly using a calibration gas comprising 3.5% carbon monoxide. 3% accuracy of 3.5% is +/- 0.105% . If diesel CO output is less than 0.1%, how is that gas analyser going to be effective in detecting the subtle difference between a diesel with a CAT and one without ?
My figures for CO emmissions come from Wikipedia so maybe we should take it with a pinch of salt for now ? http://en.wikipedia.org/wiki/Exhaust_gas
Perhaps VOSA will respecify the EGA design and limits at some future point, but for now it looks like the equipment which achieves current type approval standards isn't accurate enough to be able to detect CO changes in diesels where the current standards apply. That is not to say that there is some equipment which can measure the difference between 0.045% CO and, say, 0.03% CO, but we're talking lab apparatus standards now, and it also means there is another requirement for the EGA test gas to also meet such levels of mixture accuracy.
I guess that for now, at the very best, VOSA can only say something like 'if it's fitted as standard it must be fitted forever'...so a hollowed out DOC+DPF looks just like one which is intact, doesn't it ?
*. I might have applied the 3% accuracy in a gross way above...not quite sure from a second reading of the EGA standards now if it shouldn't be the case that accuracy needs to be 3% of the measured limit instead, which for a petrol engine is 0.3% CO.....so recalculating for 3% of 0.3 gives +/- 0.009% tolerance
Lets say a diesel without CAT produces 0.045% CO at idle and with a CAT it produces 0.01%, then I think the accuracy still isn't there in the measuring equipment. Most people like to work to at least 2 significant figures of accuracy, and that just isn't there whichever way we use the calculation. I still think that whichever way we calculate, the accuracy of existing EGA's isn't good enough
0.009% is 9 parts per million, ppm. The global CO background level is 0.05-0.15ppm, according to this EU document http://ec.europa.eu/environment/air/pdf/pp_co.pdf
The average level in homes is 0.5- 5 ppmv. Levels in city steets next to busy roads can be far higher.
This seems to suggest that even at the current levels of accuracy, EGA's can easily be confused by the background levels of carbon monoxide. I wonder if this is why there is still no requirement to measure the emmissions from a modern diesel ?
So, either way we do the caluclation, the current EGA's seem to me at least to be either too crude to measure such small levels, or they are so accurate that they are affected by local background levels of CO when trying to measure the small amounts being emmitted from a modern clean running diesel.
So, maybe the presenter in the video I posted in message #2 is right after all when he says there should be rebates given to drivers of diesels for cleaning up the atmosphere ! http://www.youtube.com/watch?v=fNO-oUHmKXU
A DPF which is just drilled through into the rear to relieve some pressure probably doesn't capture as much soot as one which is intact. The soot levels of a modern diesel with a completely drilled DPF come in at about 0.3% - 0.5% (Tested by people who's cars use the same engine as us and which passed the MOT with a fully drilled DPF)
The soot test has an ultimate failure concentration standard of 2.5% after an enhanced testing process. If the car reaches better than 1.5% soot on it's first run the enhanced test isn't even carried out and the car is automatically issued a smoke test pass. Therefore I have no need to consider that the car will fail the MOT with a drilled DPF. 1.5% soot is quite visible, I don't have any smoke at any time, regen or not.
I think the diesel technology industry has a hard time to explain just how clean diesel is now, because of the legacy of dirty diesels which have gone before. It will take more time and more fact sharing before this becomes really well known.
It's 2 weeks ago to the day that I first drilled into my DPF. 3 weeks ago I posted a message giving advice to someone which said that when their car performs an active regen they should bring the revs up to help with getting the heat up. I was wrong. My real world testing shows that raising the revs lowers the DPF temperature during an active regen.
During a forced regen, there is no load at all, but there is still a need to add regen diesel to increase temperature and I think that's why the rev's have to go up to 3500rpm during a forced regen - because there is no load to hold the revs back, with the extra fuel that is being injected as the piston is going down on the power stroke (and possibly again on the exhaust stroke) the end result has to be that some power is being generated. That power is what causes the revs to rise. I bet of the designers could get a forced regen to run properly at 2000rpm (like ont he motorway) they would have done so for many practical reasons.
I don't actually recall which poster said of active regeneration 'No, it's better to let the car do it by itself at lower revs', but he wasn't listened to by anybody, least of all by me. Whoever he is, he's right. Well done that man
2 weeks ago, if someone had of asked me what clogging % meant I would have said 'soot loading'. That was wrong too.
This past 2 weeks has been educational for me and helped me to understand a little bit more of what's going on. Some of the data defies common theory still today. In time I hope the truth about those other uncertainties might also become known.
It certainly won't take much effort for a person in the position to resolve the remaining controversies to find the facts, and share them