Smokey Diesels on hot days?

Unread post by **CitroJim** » 17 Jul 2006, 19:03

I've noticed today, especially, that nearly every new or nearly new diesel powered car, especially "Chelsea Tractors" are smoking quite significantly. An 06 plate Jeep of some description and an 02 plate Merc were smoking like chimneys.

Is this to do with the hot weather? In my days in Cyprus every Diesel powerd truck large and small smoked like old billy all the time and I used to put it down to poor fuel/maintenance. Now I'm not so sure.

I'm surprised that modern machinery with its whizz-bang injection technology smokes like this when the good old XUDs in my posession show no sign of smoke on this day or any other and that is on low-tech mechanical pumps.

Stuart McB · Unread post by **Stuart McB** » 17 Jul 2006, 19:59

Got to agree, this morning a couple of Auid A6's went past me- same thing, very smokey. Our works Reno Megan TD was fine though. Curious.

Kowalski · Unread post by **Kowalski** » 17 Jul 2006, 22:36

Air gets less dense when its hotter, so its a bit like having a dirty air filter. A modern diesel with an air flow meter should detect the thinner air and adjust / limit fueling accordingly, perhaps modern diesels are just better at getting close to the smoke limits rather than actually being any cleaner...

Stewart(oily) · Unread post by **Stewart(oily)** » 19 Jul 2006, 17:16

I seem to have spotted a few smokey diesels out there during this hot spell, I had occasion to call on full power in the BX TD recently and was a little disappointed, mind you it was on about 75% Biodiesel at the time which may affect ultimate power output.
Stewart

nick · Unread post by **nick** » 19 Jul 2006, 18:06

Could it be that the atmospheric conditions, ie bright sunlight & hot dry air, are making the smoke more visible & more airborne, rather than actually making the engines produce more smoke?
Just a theory!

VAG TDi's do seem particularly smokey for 'modern' diesel engines though.

sub42 · Unread post by **sub42** » 19 Jul 2006, 22:12

Not about a car, but I saw a coach today from a well known company absolutely belching out the old smoke! It enveloped several cars, which had to stay stationary for about fifteen seconds before they went on their way! But then thats one of those 'cleaner' ways to travel. The reasoning being that because it carries 55 passengers, its allowed to be 45 times more smoky and polluting than a car or van. The fact that you can't see behind them is beyond all reckoning! Have been told that the worst ones burn five litres of oil between Luton airport and Heathrow......

406 V6 · Unread post by **406 V6** » 19 Jul 2006, 22:22

It occured to me (but by no way a scientific approach) that as warmer air is able to hold more water vapour (moist), the smoke coming out from diesels might aglomerate more in contact with the water particles suspended in the air.
Juyst a thought, though...

ssray · Unread post by **ssray** » 30 Jul 2006, 19:57

A diesel likes to run lean-too much fuel means too much heat and you see this as smoke-if its really hot the air is going to be less dense but the same amount of diesel going in so its a bit hot and you see smoke.
its the opposite of a 2 or 4 stroke.
it confuses me though.
Ray

TomH · Unread post by **TomH** » 31 Jul 2006, 20:21

lots more smoking diesels and hot weather.... doesn't take a genius to see why nitrogen dioxide pollution is through the roof!