Good morning all.

I've been reading about having lots of smoke, I think I have an average amount and I could probably use a new air filter but can someone explain why smoke = higher exhaust gas temperatures and why this is bad.

For some reason I cannot post in the ask a tech section.

Thanks in advance.

Flip.

I'm guessing it's not good to have a massively hot engine/turbo, it'll just **** things.

Matt

Smoke is unburned fuel suspended in the exhaust gas stream, in the context of modern direct inject diesel engines that smoke is symptomatic of that fuel being injected too late to be used up during combustion, therefore combustion took place in a lean condition and that is why the EGT's are high.

It happens when tuning goes bad, no amount of fannying around with air filters will make any difference.

High combustion chamber temperatures cause damage to the cylinder head, pistons, valves and valve seats, they also damage the turbo inducer.

So the next time some moron tells you "No smoke, no poke", just punch him full in the face.

So the next time some moron tells you "No smoke, no poke", just punch him full in the face.

Bahahahahaha ******* hilarious

Smoke is unburned fuel suspended in the exhaust gas stream, in the context of modern direct inject diesel engines that smoke is symptomatic of that fuel being injected too late to be used up during combustion, therefore combustion took place in a lean condition and that is why the EGT's are high.

It happens when tuning goes bad, no amount of fannying around with air filters will make any difference.

High combustion chamber temperatures cause damage to the cylinder head, pistons, valves and valve seats, they also damage the turbo inducer.

So the next time some moron tells you "No smoke, no poke", just punch him full in the face.

It's refreshing to have someone who understands diesel engines on the forum lol!

What some tuners tend to do is dump as much fuel into each injector, and extend the injection duration in thinking it will burn, however, at that point, the pistons travelling to BDC, losing conpresson....and how do diesels work? They ignite on compression....

very interesting, in relation to "no smoke no poke" being the wrong idea why is it that some of the highly tuned fabias on the forum seem to have a lot of smoke??

matt

ps i am not being sarcastic

I was wondering that. Unless of course, it means that they could get the same amount of power, with less fuel. And the smoke is excess fuel which is being injected in hope of getting more power?

I've never seen proper footage of it - but do the Audi R8/Peugeot 908(?) race cars smoke, or are they fueled so they can actually burn everything cleanly?

very interesting, in relation to "no smoke no poke" being the wrong idea why is it that some of the highly tuned fabias on the forum seem to have a lot of smoke??

matt

ps i am not being sarcastic

Whoevers mapped the car has requested for the fuel to be injected, so they're to blame.....

I know in some cases it's almost used as anti lag to bring a big turbo online though, and as soon as it's boosting, the black smoke dissapears (tractor pulling).

In older engines, it's not as easy to control injection duration (mechanical fuel pump direct injection, for example).

Typically, in the never-ending quest for headline grabbing BHP figures, idiot tuners apply petrol engine principles to diesels, i.e. they try to make them rev harder.

On a petrol engine this is relatively simple, since flame front propagation and therefore the speed of combustion is basically constant, as the engine speed increases you simply advance the ignition further to allow time for this combustion process to occur fully while still doing useful work, the practical limit is reached at the onset of detonation.

On a diesel engine you can't do this, the only control you can exercise over the combustion process is to choose when you inject the fuel, given that the flame front propagation of a diesel/air mixture is slower than petrol/air you reach a hard limit where there simply isn't enough time for all the fuel to be burnt before the exhaust valve is opened and that unburnt mixture comes out as smoke.

On old-tech diesels there is no practical limit to the size of the injectors you can fit and you can therefore shove as much air into the cylinder as you like, these engines still don't rev, they just produce gigantic amounts of torque.

Think about tractor pulling and the huge plume of black smoke that spews out of them as the boost comes in.

Finally you must also remember that when you put your foot down you're asking the ECU to make the engine go faster, so the ECU looks at all it's sensors then looks up the corresponding map value and does a calculation to determine how much fuel to inject and when. If that map has been crudely written or there are some faulty readings from sensors then the engine will smoke like a chimney. This is one of the reasons why EGR delete is such a bad idea since the ECU is considering this in it's calculations even though it's not actually present.

Even with a really good map there's always still a small amount of smoke, for example even an unmapped vrs with still smoke slightly.

Do they tend to smoke more higher up the revs as the combustion process is simply happening too fast for all the fuel to be burnt and the turbo running out of puff so less air so the smoke appears worse?

I was wondering that. Unless of course, it means that they could get the same amount of power, with less fuel. And the smoke is excess fuel which is being injected in hope of getting more power?

I've never seen proper footage of it - but do the Audi R8/Peugeot 908(?) race cars smoke, or are they fueled so they can actually burn everything cleanly?

They will be correctly fuelled for optimum performance, this is a result of having a perfectly set up map developed over thousands of hours of testbed time.

They will probably still smoke slightly under certain transient conditions, but it will be very brief since wasted fuel means more stops.

Edit: Racing ECU's also use very high resolution maps and high sample rates so they're much more accurate.

Edited 27 August, 201114 yr by sepulchrave