Extra diesel is only added in response to increased boost pressure - the pump does not pre-empt the turbo!
What happens is that diesels driven gently accumulate soot in the exhaust, when you give it some welly, the exhaust velocity is sufficient to shove this soot out of the tail pipe, hence the big black cloud.
Of course, poorly maintained engines can smoke, but it is usually down to a dirty air filter, or on higher mileage cars worn injectors.
Modern diesels win hands down on emissions over peteol engines - especially those such as the PSA 2.2 HDi fitted with a soot trap.
Richard
(Let's see what response that stirs up from the petrol-heads...)
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There was an old thread about how to clean diesel smoke deposits off the back bumper. No one seemed to question why diesels did this, or responded to my question, Is smoke still a pollutant? Or only if emitted by a petrol engine or a factory?
And what about that research not long ago which apparently found a link between driving a diesel taxi all day and increased cancer risk?
Just asking, not trying to be provocative, much.
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Ok, here we go again.
Visible soot is around ton microns in diameter. It sticks in the mucus of the nose, and triggers the body's cough response if breathed in in quantities. This is a good thing. Your body protects itself this way.
Petrol engines also produce soot, but they are invisible to the naked eye. So small are they in fact that they get right down into the lungs, and pass through into the blood stream. Now what you don't want in your blood stream is half-burnt hydrocarbons.
I went to Los Angeles last weekend. Within an hour I was sneezing, coughing, and had a tight chest. I'm a fit thirty-four year-old, and LA is not known for its high number of diesel engines. Make up your own mind.
Chris
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I have a 3 month old Citroen C5 2.2 HDI (with particle filter) It has now done 4000 miles. If I poke my finger up the exhaust pipe and wiggle it around, it comes out spotless. The inside of the pipe is exactly like a new exhaust system off the shelf. I have never seen smoke coming from it. Needless to say, the car goes like stink, averages 40mpg without trying (50+ if I doddle)
It is also the quietest car I have ever had (much quieter than my previous - Petrol Xantia!) Well impressed!
Graeme
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Hi Graeme,
I own same style of C5.
I am worried by 2 things thta have come to my mind following your post:
1) I would never have thought of sticking a finger into a car exhaust.
2) Now you have mentioned it I'm curious to try!
Regards
Vercin
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Hi Graeme, I own same style of C5. I am worried by 2 things thta have come to my mind following your post: 1) I would never have thought of sticking a finger into a car exhaust. 2) Now you have mentioned it I'm curious to try!
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You don't have to do it with the engine running, Vercin!!!
My wife's Citroen AX diesel has done 93k and doesn't smoke at all.
I have had smoky diesels before but they are getting progressively less smoky all the time.
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Up to a few years ago all diesel cars were indirect injection for the very reason that engine manufacturers had not at this stage been able to produce a direct injection diesel suitable for cars, which gave acceptable levels of noise, vibration and smoke.
Rover were the first (arguable)with the Perkins Prima engine fitted to Montegos and Maestros. These were later turboed and emit black smoke on acceleration which can't be cured.
Perhaps mainly due to the big petrol hikes in price other manufacurers came up with their more advanced DI engines which with management systems cured the problem.
Uncle Gordon then had nightmares of us all driving diesels and quickly put a stop to that...hence the fuel strike.
alvin
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"These were later turboed and emit black smoke on acceleration which can't be cured."
Like this, you mean? :-)
www.tractorpulling.co.uk/
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Hi Vercin!
I think I read about this somewhere and like yourself, couldn't resist the temptation!
You'll find the 2.2 C5 has a twin exhaust pipe, by the way - choose either or both!
Do let me know if yours is the same - perhaps I've got an oddbod one!
Regards
Graeme
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Hi Vercin! I think I read about this somewhere and like yourself, couldn't resist the temptation! You'll find the 2.2 C5 has a twin exhaust pipe, by the way - choose either or both! Do let me know if yours is the same - perhaps I've got an oddbod one!
Hi Graeme,
I have now tried the 2 finger test!
Regret to inform you that after 5,300 miles both exhaust pipes produced slight amounts of soot.
Hope this is of use
Regards
Vercin
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".. triggers the body's cough response if breathed in in quantities. This is a good thing.."
Well, that should give the smokers a new line of defence! (cough, splutter)
I do know that garages habitually run diesels really hard for a few minutes before doing their MOT emission tests, which does seem to defeat the object. (One car engine I know of chose this moment to lose its cambelt, much to the embarrassment of the mechanic.)
The thing about diesels I notice most is that the exhaust smell makes me physically sick. I think this is my body's response to the fact that it's poisonous! It's not for nothing that most modern diesel cars have their tailpipes pointing downwards...
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The thing about diesels I notice most is that the exhaust smell makes me physically sick. I think this is my body's response to the fact that it's poisonous! It's not for nothing that most modern diesel cars have their tailpipes pointing downwards...
I remember following my boss in his H reg Rover 216 and I had to stop because the fumes he was pumping towards me made me feel really bad - presumably pre-cats. With modern cars SWMBO just acusses me of farting..
As for tail pipes pointing down, there are a large number of petrol cars that employ this technique. Conversely there are a number of diesel cars that have horizontal pipes (eg 306TD)..
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>I do know that garages habitually run diesels really hard for a >few minutes before doing their MOT emission tests, which does >seem to defeat the object.
This is set out by the governement as part of the test - to dislodge any soot in tail pipe they are supposed to be testing the engine, not the stored soot after all. Note that petrol cars have to pass a myriad of standards in their emissions tests - CO, CO2, hydrocarbons etc, whereas diesels only have to pass a 'smoke opacity' test - the rest is taken to be OK since diesels do not go 'out of tune' as easily as petrols.
>(One car engine I know of chose this moment to lose its >cambelt, much to the embarrassment of the mechanic.)
All too common - especially when the test was first introduced - they are supposed to ask you about the cambelt first, and it's at your risk. Nice, eh?
>I think this is my body's response to the fact that it's >poisonous! It's not for nothing that most modern diesel cars >have their tailpipes pointing downwards...
A couple of lungs full of petrol emissions will probably make you very, very, sick, if not kill you, due to the CO content (although this is much less since the advent of cat converters - the 'clean' device that increases CO2 - the government's only pollutant of choice for determining emmissions related tax). The equivalent from a diesel engine may make you cough, and possibly give you black snot, but it won't make you keel over instantly.
Ah well, keeps up a lively debate (as long as you are not breathing petrol exhaust fumes....!!)
Richard "Diesel Boy" W
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A quick 'finger up the exhaust pipe' check on the cars in our carpark shows that all the cars less than 10 years old have clean pipes, including my K reg petrol Volvo with 260,000 miles on the clock.
All old ones are sooty, whether petrol or diesel.
So someone has answered my query - diesel smoke may look smokey, and it may cause black stains on the back of the car, it may make peple feel sick and cough, but it is not as dangerous as the invisible emissions from petrol engines. That seems a fair point.
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Cliff.. hope nobody saw you in the car park. Would have made a scene for Victor Meldrew.
alvin
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"I do know that garages habitually run diesels really hard for a few minutes before doing their MOT emission tests, which does seem to defeat the object."
The whole object of the MOT emissions test is flawed because the test simulates an open road run (mainly of interest to cows) whereas what we should be interested in is what the engine is pumping out after crawling through town traffic for ten minutes (mainly of interest to humans).
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Los Angeles -photochemical smog -a mixture of Ozone and hydrocarbons nothing to with diesels.
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Cliff
Cancer is probably nothing to do with the diesel taxi, more likely to be the 40 fags a day, stress of driving in modern traffic and shouting at anyone who dares to do any manoeuvre within 10 yards of them
:o)
Terry
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... and getting no exersize...
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Diesel MOT emissions test doesn't replicate any real driving conditions as it done at full revs with no load.
The taxi driver probably got his cancer from breathing in the benzene that was put into unleaded to replace the lead. I doubt the fact that he drives a diesel had anything to do with it unless he was sticking more than his finger up the exhaust.
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I have driven a Picasso HDI (90hp, no intercooler or particle trap) and loved the drive.
I still think there is a place for petrol engines; for people who do few miles per year and so won't save any money because the diesel may cost more to buy, be serviced more often, cost 3 or 4 p more per litre, but do 30% more mpg.
Ben
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Best thing about diesel is no catalyst and with old perkins 2l no ECUs either. Before I always do a 10 mile Italian tuneup to clear out the accumulated debris and ensure engine hot. MOT emission this time just above 2.5 units first run, but diminishing and below test limit in next runs. However when next to my brothers new Fiat van, his complete lack of smoke puts mine in the shade!
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After my post of 8th August re Rovers and smoke I have to say that the other day I was stuck for miles behind somebody towing a burger bar and with some clown 10 feet off my back bumper. When the chance came for an overtake I put the pedal to the floor and went for it. When I looked in my mirror the complete road had disappeared in a huge cloud of black smoke and the bloke who had been hassling me couldn't even see to overtake. It was like a WWII film with a destroyer laying a smoke screen! No smoke now and 45+mpg so I guess it was just a build of clag from dawdling in traffic.
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Wonder if you are using City Diesel or equivalent. The liquid hardly smells cf ordinary diesel and is very light colour. I found it halved smoke emissions on my Perkins diesel. Also use Millers Diesel additive as recommended by HJ.
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AH. If your query about what diesel I use was for me I use Safeway and Tesco and always use Millers additive; Perhaps the 105,000 miles on the clock is something to do with it, although it is totally smoke free 99% of the time.
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