Diesels accelerating - big clouds of black smoke- explain??

[heebeegeetee]

otolith said:

heebeegeetee said:

otolith said:

Heebeegeetee said much the same thing. Can someone provide me with a reference for this?

Well i can't, other than to search the same as anyone else can, because i was only following the diesel argument closely some 10-15 years ago, before th'internet was in widespread use. I used to have to use print for my information. .

The differences in pm production between the 2 types of engine hasn't changed that much AFAIAA, rather than it's now how the pms are dealt with after combustion.

Everything I've seen suggests that diesel engines produce particulate matter in very much larger quantities than petrol engines (with the exception of the new direct injection petrol engines for which particulates will now be subject to emissions limits for the first time). I couldn't find anything saying that the difference was just an artefact of the size range of particles measured, so I was hoping someone could point me to one.

heebeegeetee said:

Historically, diesels have always been far cleaner than petrols

Historically, diesels have always been far dirtier for some pollutants and far cleaner for others.

Diesels have always been worse for NOx and particulates. Petrols have always been worse for carbon monoxide and hydrocarbons. The regulations have tightened for both and are converging.

My understanding is that in terms of weight, diesel produces more pm, and those pms are larger and heavier. Petrol engines produce numerically more pm, which are lighter, remain airborne for longer, and when breathed in can travel further into the lungs.

My recollection is that exhaust gases could be broken down into about different constituents, diesel was worse in 2 of those and better in 6. But I honestly can't recollect what those constituents are now, but i'm sure if i had time i'm sure we'd both soon find out.

Of the 2, diesels were worse in Nox with new engines, but after some useage the Nox used to come down. I do recall that the then head of VW stated that this happens at about 12,000 miles of use. What happens nowadays though, i really have no idea and tbh, not that much interest either.

I think possibly the greatest source of harm comes from when we're fuelling our vehicles. Petrol has benzene added to it, which the World Health Organisation says has no known safe level of use. IIRC to used to recommend that no more than 5 parts per million should be used, but petrol used to have several hundred parts per million.

The levels have subsequently reduced now though, and again i have lost touch with what the figures are. To put things very simply though, Benzene causes cancer and cancer will strike 1 in 3 of us (though for whatever reason in my family the levels are far higher - our rate must be more than 2 in 3, i would say. And no, they haven't all driven diesels. )

But i'm sure we can all while a few hours away googling pollution figures if we want to.

Edited by heebeegeetee on Monday 6th September 17:31

[frosted]

HellDiver said:

frosted said:

it needs to regenerate every 3-4 days

That's pants. There's something wrong with your car.

My Lancer (fitted with a VW 2.0TDI PD 140hp, factory remapped to 170hp) didn't need regenerated once in the time I had it (8 months, 12k). That was mixed motorway, urban and rural driving.

Are you for real or can you not read ?

[PKLD]

Ummm my 09, 318d don't smoke and when eh 'pushed on' it goes down to 37mpg with brief periods down to 28 but over the last 5000 miles it's averaged 48mpg (on the dashboard).

No smoke confirmed by g/f when trying to stay in front of her when she's in her TT!

[Pigeon]

Munter said:

As I understand it. To make the most power a diesel "over fuels" a lot. That excess fuel doesn't burn properly as theres no oxygen to mix with it. And you get soot.

Something like when it's not sooty, you're only using about 1/2 the oxygen to burn all the fuel. More fuel to less oxygen = more soot.

It's not lack of oxygen, it's the difficulty of getting all the fuel vaporised and thoroughly mixed with the air in the short time available. Petrol engines don't have a problem as the mixing and vaporisation process begins as the fuel is being drawn into the cylinder and there's the whole of the induction and compression strokes to get it done in. Diesels have to do the whole thing in about 20 degrees of crank rotation and if there's too much fuel they can't manage it. Even at full whack a diesel is running about 50% lean of stoichiometric.

mini me said:

In fact I do believe it's the opposite there is much more oxygen left in diesel exhaust If it's running right and this is partly why they are more efficient. i.e less fuel is injected for the same amount of air.

Diesels are more efficient mainly because they run much higher compression ratios and because they don't have the pumping losses on part throttle.

If anything the less-fuel-for-the-same-amount-of-air makes them less efficient, because you have to churn more air through the engine to burn the same amount of fuel and there are more losses associated with that. But the high compression and lack of throttle plate have a much greater effect in the other direction and they work out more efficient overall.

pugwash4x4 said:

They run far richer at WOT as they can handle the fuelling- they run much leaner off WOT because you don't get the attendant heating problem you do with leaning a petrol engine- quite the opposite. Lack of throttle butterflys always helps!

Diesels never run rich, see the first part of my reply. They are always very lean in petrol terms even when running at their richest.

The reason they "run much leaner off WOT" is nothing to do with "heating problems", it's simply because they regulate the power output by reducing the amount of fuel while keeping the amount of air the same.

[busta]

I can set the amount of smoke my volvo makes by twisting a few screws. More smoke=more poke to an extent, but i'm getting the hang of fiddling with other pump settings to get the same poke with a bit less smoke as it can be a bit ridiculous at times! I still can't get it to smoke on full boost though (1.5 bar at the moment). Maybe the pumps just not up to it.

It's also quite nice being able to wind it all back down for MOT emission tests or long trips where economy matters (I can get anything from a steady 40mpg to consistent 25mpg, depending where I have the main fuel screw )

Was rather amusing when I had an A4 cab tailgating me with the roof down the other day. Up hill, off boost in 5th gear soon had him backing off about 50 yards.

[aw51 121565]

otolith said:

F i F said:

You DO all realise that petrols also produce particulates don't you?

Just that the particulates they produce are smaller and thus less visible to the naked eye.

It's because of a carefully selected particulate size that diesels show higher particulate production, if a different size were selected the results would be different. In other words the particulates produced by petrol engines are too small to be caught by the measurement process. Doesn't mean that they aren't there or that by weight they may be more.

Heebeegeetee said much the same thing. Can someone provide me with a reference for this?

Try googling "PM2.5" and "PM10" to get a feel for the different sizes of particles mentioned in the thread, also "quality of urban air review group". The QUARG report gives a lot of anti-diesel propoganda.

Petrol engines chuck out a load of PM2.5s, which are all but invisible and get much further into the lungs being smaller than PM10s - and also nastier in nature than the PM10s from diesel exhausts. PM2.5s are easily measured; they are also easily overlooked as the general public don't see them belching from petrol exhausts . But they are there.

And as for posters talking about diesel engines operating at WOT... As others have alluded to, diesel engines generally don't have a throttle plate nor any other restriction to airflow into the engine apart from the ducting itself as their speed is controlled by amount of fuel injected.

Technically, diesels always operate at WOT, which isn't the same as pressing the accelerator pedal to the floor (although in a petrol engine the second leads to the first, on diesels there's no throttle to be opened by the accelerator pedal linkage usually hence permanent WOT) .

[HellDiver]

frosted said:

HellDiver said:

frosted said:

it needs to regenerate every 3-4 days

That's pants. There's something wrong with your car.

Are you for real or can you not read ?

No, are you stupid and unable to recognise your car is fked?

[10 Pence Short]

heebeegeetee said:

10 Pence Short said:

You have to wonder what sort of MPG some drivers really get from their diesels when they drive in that way? I wouldn't be surprised to see it dip well into petrol territory.

But they'd be driving as equally uneconomically in a petrol, surely?

Er, no- my whole point was that the power delivery of a modern diesel allows people to be lazy with regards to throttle sense. Power delivery from a NA petrol engine doesn't suit being so lazy, hence people naturally have to drive differently.

It's a criticism of drivers rather than the engine characteristics, but then humans are often like water- they take the path of least resistance.

[otolith]

I can't find anything more up-to-date, and I realise that the references in this paper are ancient and that engine tech has changed radically, but it would appear that:

• diesels produce much higher PM10 emissions than petrols
• PM10 is < 10 microns and includes PM2.5
• Almost all diesel PM10 emissions are also PM2.5

"Approximately 98% of the particles emitted from diesel engines are less than 10 microns in diameter, 94% less than 2.5 microns in diameter, and 92% less than 1.0 microns in diameter (ARB 1997).'"

http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles...

So PM10 includes PM2.5, and diesel PM10 is almost all PM2.5, and diesel PM10 is substantially higher than petrol PM10, I'm not seeing support for the idea that petrol PM2.5 emissions are higher.

Can anyone find more recent data? Do modern (non-GDI) petrols throw out much higher levels of small particles than older ones, or have modern diesels radically shifted the frequency distribution of their particle sizes towards larger particles?

[frosted]

HellDiver said:

No, are you stupid and unable to recognise your car is fked?

I can see that your a simpleton , however I'm my two previous posts I said I live in London , I don't see 40mph for longer than 2 minutes unless I go out of London . You seem to think that because your chav mobile gets driven in Yorkshire or some far away sticks in the middle of nowhere , you can comment on something you have no idea about ?

I have already said that if you live somewhere like Manchester you shouldn't worry about the dpf

He asked in my opinion , of someone who lives in the city , not someone who shagges sheep when no one is looking

So it turns out the only STUPID person here is YOU

[pugwash4x4]

Pigeon said:

Diesels never run rich, see the first part of my reply. They are always very lean in petrol terms even when running at their richest.

The reason they "run much leaner off WOT" is nothing to do with "heating problems", it's simply because they regulate the power output by reducing the amount of fuel while keeping the amount of air the same.

of course diesels run rich- 14.7:1 stoichomatic is irrelevant to Diesels- fundemantally they don't work the same way.

you can overfuel a diesel engine- therefore it runs "rich"- maybe the work rich is wrong, but its essentially pushing more fuel into the cylinder than can be burnt without the help of an accelerant (a big intercooled turbo ie the acceleran in this case is compressed cool oxygen, or perhaps propane) - at this point you get big puffs of smoke as the diesel is only partially combusted.

[y2blade]

10 Pence Short said:

heebeegeetee said:

10 Pence Short said:

You have to wonder what sort of MPG some drivers really get from their diesels when they drive in that way? I wouldn't be surprised to see it dip well into petrol territory.

But they'd be driving as equally uneconomically in a petrol, surely?

Er, no- my whole point was that the power delivery of a modern diesel allows people to be lazy with regards to throttle sense. Power delivery from a NA petrol engine doesn't suit being so lazy, hence people naturally have to drive differently.

It's a criticism of drivers rather than the engine characteristics, but then humans are often like water- they take the path of least resistance.

I can kind of answer that

I have a brace of Volvo (2.3 petrol T5 and a 2.4 Diesel D5) so pretty like for like (or as like for like as needed for this sort of thing)

same driver, same driving manner and driving speed... results for both are as follows

on a long motorway run = T5 31mpg - D5 61mpg
on my rural 20min commute = T5 27mpg - D5 51mpg
on a spirited run = T5 17mpg - D5 41mpg

all my figures are measured at the pump/wallet (NOT OBC)
http://www.fuel-economy.co.uk/calc.shtml


In all situations the Fuel economy of the Diesel is better than the petrol
Performance wise the two are pretty much identical up to 140 (at that point the D5 is topped out yet the T5 keeps on pulling)

Edited by y2blade on Tuesday 7th September 16:55

[Sorentowner]

I own a Kia Sorento and is puffing out black smoke. Recently serviced. Brought in to authorised garage for a thorough check. Injectors are ok. Changed the intercooler but doesn't solve problem. Ran 300km nonstop but smoke remains upon acceleration. What possible problems could cause this? Stuck valve. But it was top overhauled a year ago. Think another visit to the garage.