On 17/04/17 10:06, Chris Hogg wrote:
On Mon, 17 Apr 2017 09:23:02 +0100, "Brian Gaff"
wrote:

Well, I think to be honest they would need to limit this to the very
polluting.

Did they not develop a particulate filter some years ago, for this problem,
or is the issue that its very costly to make and needs to be cleaned out too
often.

Its interesting, living near an industrial estate, to note that you can
stand right by modern diesel exhausts and they do not smell or make smoke
etc, but if its a few years older, such as you might find in post office
vans, you are choking in seconds.
Modern diesels are a lot better, just not as much better as the perfect
test results would have you believe of course.
Brian

AIUI modern diesel cars have a filter to take out the PM10 or PM2
carbon particulates. But like any filter, after a while it gets 'full'
and starts to choke. Again AIUI, it requires a longish run from time
to time to get the filter hot enough to burn off the carbon. If you
only ever do short runs, you may have problems.

I have a ten-year-old diesel (Ford Fusion). It has no filters of any
sort. When I replace it, I'll get a petrol car, simply because I only
do short journeys and the obligatory carbon filter would probably get
bunged up. I don't particularly relish having to drive an unnecessary
and longish journey, weekly, simply to clear it.

But particulate carbon isn't the only problem. Because of the hotter
combustion temperatures, diesels emit more NOx, which seems to be the
main point of issue ATM. I gather there may be catalytic NOx filters,
but the current fuss suggests they don't work very well.



I've had 2 10 year old cars with DPFs and they've been fine - one
sometimes demands a long run to clear it then is OK for ages.