Dieselmief und Nachrüstkat | Posts 16+

Hi Albrecht,

I don't want to argue :

But there's one thing I still don't understand:

Soot is produced when the mixture is not evenly distributed. The higher the "load," the more soot -> uneven distribution, but in this range, the EGR (Exhaust Gas Recirculation) system is active -> so less NOx. Therefore, the logical conclusion is that the combustion temperature is higher in the lower load range due to finer atomization, which leads to increased NOx formation? Or is it because there is no longer an excess of oxygen in this range? At what point is there less oxygen in the combustion chamber than is necessary for complete combustion?

"Didn't Bertil also confirm that the droplets are larger when there is a higher flow rate through the nozzles?"

Best regards, Christian.

haehnlein wrote:

Didn't Bertil also confirm that the droplets are larger when there is a higher flow rate through the nozzles!?

Stop, the droplets aren't getting bigger; instead, the mixture becomes "supersaturated" and precipitates out, forming soot in the process.

For diesel engines, it's the same as for gasoline engines. In the partial load range, you need to control the combustion process to regulate NOx emissions. This is achieved using Exhaust Gas Recirculation (EGR).

Now, the gear-based idea from Volkswagen is already being criticized by other manufacturers (too noisy, too heavy, unstable, etc.). So, Volkswagen is once again being blamed for pursuing a 'special path' (just like with the PD technology).
By the way, Formula 1 engines used to have gears before pneumatic valve control systems!!! Why do you think that was?

Well, because Formula 1 has plenty of money to spare. In mass production vehicles, cost is a factor, and gear-driven systems are simply too expensive.

'That's also the problem with particulate filters. FAP uses an additive to regenerate the filter, but another approach would be to inject fuel into the exhaust stream to increase the exhaust temperature and burn off the filter. This not only consumes fuel but also increases emissions. That's why there are no D4 engines...'
Even the NOx storage catalyst in gasoline engines needs to be regenerated. That's why Shell Optimax has a lower fuel consumption, because it is low in sulfur and therefore does not hinder the loading of the catalytic converter. One octane more doesn't make a difference .

Bertil has already explained the concept of 'Russbildung' wonderfully.
@haehnlein: Actually, the mixture doesn't really become too rich, not even in gasoline engines. However, in diesel engines, as the fuel-to-air ratio increases, the excess oxygen decreases (obviously), and due to the inhomogeneous distribution of the fuel, the mixture becomes locally too rich, leading to soot formation. BDI (which actually means BDE) don't have this problem because they switch to homogeneous operation at higher loads.
The EGR valve is present in both engines, and only makes sense due to the D3 or D4 models. Otherwise, it has no purpose and actually increases fuel consumption.

Bosch is researching a fuel injector with an adjustable cross-section. This would reduce the droplet size, especially at partial load (which involves lower injection pressures). The initial prototypes are working, but they are far from being ready for mass production.

CU Gremlin.

Hi there,

Here's an idea:

If the diesel fuel were heated to, for example, 300-400°C before injection and then injected, it would have to vaporize at the moment it exits the nozzle and distribute itself homogeneously due to its high velocity before it ignites. Then the droplets would only be molecular in size, right? Wouldn't that lead to a cleaner combustion process?
It remains unclear what influence sulfur has on the combustion process. I read on www.biodiesel.de that a TDI engine can only be classified as having lower emissions by using biodiesel. This is supposedly because biodiesel is truly (almost) sulfur-free.

What is the opinion on this?

Regards,

Eike.

The higher the 'load,' the more soot -> leading to inhomogeneous distribution, but in this range, the EGR is too high -> resulting in not much NOx. So, isn't the logical conclusion that the combustion temperature is higher in the lower load range due to finer atomization, and therefore leads to increased NOx formation?

The wording is slightly different in the VKM script; here's an image from it:
(The diagram shows that soot and NOx emissions increase significantly at full load, while CO and HC emissions are slightly higher at partial load compared to full load.)

These values are obtained without EGR or catalytic converter.

High air-fuel ratio = partial load (idle) = low combustion temperature = less NOx... but even that is still too much, which is why EGR is used.

When running at full load, there is significantly more NOx produced, but because modern emissions tests do not involve driving under extreme conditions, car manufacturers are less concerned about emissions at maximum power output.
Specifically, a modern TDI engine has so much power that it can almost pass the emissions test while idling .


Regarding homogeneous diesel combustion: It's true that work is being done on it, but currently, it doesn't yet function properly. (The professor believes it might be possible within 20 years).
The theory of homogeneous diesel combustion suggests that it would produce zero soot and zero NOx emissions. I hope we don't all get lung cancer by the time that happens.

Best regards, Ernst.

Hello Christian,

Quote:

Soot is produced when the mixture is not evenly distributed, okay. The higher the "load", the more soot

.

Okay, also zusätzlich dazu gibt es einen geringeren Luftüberschuss im Vergleich zum Betrieb unter Teil Last.

Quote:

Inhomogeneous distribution, but the EGR is in this area -> not as much NOx

"Incorrect, because the combustion temperatures are generally higher with a higher load, which results in MORE NOx. However, you can't use exhaust gas recirculation (EGR) to reduce NOx when operating at high loads, because you need sufficient oxygen (air) to burn the fuel. At partial load, you essentially replace the excess oxygen with exhaust gases, further reducing temperature peaks. Nevertheless, the overall temperature level is still much lower, which is why disconnecting the EGR system cannot cause any harm ."

Bei Diesel hat man immer eine Ruß-NOx Schere: d.h. Maßnahmen zur Verringerung der NOx-Emission (z.B. AGR) führen zu einer Erhöhung der Ruß Emission. UmgeIt works the same way.
The developers' goal is to optimize this process and minimize both aspects as much as possible. One approach is to achieve a homogeneous mixture, for example, by using variable nozzle hole diameters, as Cremlin suggests. Of course, all of this is still under development, but it will happen.

Best regards, Albrecht.

Okay, you've won .

But regarding taxes: The course of the exhaust composition in the diagram confirms that exhaust taxes are purely a matter of politics . Only those who do not drive their diesel engine above 2000 rpm are truly doing something for the environment, regardless of whether it's a PD or TD!!

Best regards, Christian.

haehnlein wrote:

... But regarding taxes: The course of the exhaust gas composition in the diagram confirms that exhaust emissions tax is purely a matter of politics . ...

Yes, but everyone participates (regardless of which political party is in power)!

Hi.

The trend in the exhaust composition shown in the diagram confirms that emission regulations are purely a matter of politics. Only those who do not drive their diesel engine above 2000 rpm are truly doing something for the environment, regardless of whether it's a PD or TD engine!!


Let's just say that around 2000 rpm, it produces the least emissions (within a range of 1600-2600 rpm). Unfortunately, I don't have a particularly impressive diagram showing the relationship between engine speed and emissions.

The diagram above indicates that one should not accelerate fully to protect the environment, regardless of the engine speed.

The catalytic converter burns off the increased levels of hydrocarbons (HC) and carbon monoxide (CO) that are produced during partial load operation.

And the EGR system further reduces NOx emissions by up to 90% under partial load conditions! The slightly increased amount of HC is then burned again in the catalytic converter.

Basically, when driving in a 'normal' way, you don't really need to worry about emissions because the car manufacturer has already taken care of that.
Best regards, Ernst.

Ernst S. wrote:

The diagram above indicates that one should not accelerate fully to protect the environment, regardless of the engine speed.

Hi Ernst,

It's true that thanks to EDC, there's a difference whether you give full throttle in 5th gear at 50 km/h or at 180 km/h – it's also dependent on the engine speed...or am I wrong ?

Best regards, Christian.

That's correct. In both areas, the Electronic Control Unit (ECU) reduces the maximum torque to lower emissions.
Mainly due to the soot, which is produced both at too low and too high engine speeds.
HC and CO emissions tend to be higher at low engine speeds, but they are not a problem.

Overall, the mid-range RPM is the best. That's why you get the highest torque in that range.
Only the NOx emissions are out of line. Unfortunately, this always happens at the highest torque level.

However, the dependence on load is much greater than the dependence on speed, which is why driving at full throttle is always bad.

If it weren't for the fuel consumption, and therefore the CO2 emissions. Because of that, you should probably shift to a higher gear, even if you have to press the accelerator more. So, you can't really do everything right.

The best compromise is achieved at medium engine speeds (around 2000 RPM) and moderate loads, (and with a catalytic converter and a functioning EGR ).
Best regards, Ernst.

One might expect that 'progress' would also involve the use of intelligent lightweight construction techniques. A 3L Lupo enhanced with expensive magnesium parts still weighs a good 100kg more than a Golf1, and offers significantly less space. Furthermore, it doesn't include features like power steering, electric windows, or air conditioning. And I doubt that occupant protection can only be achieved through massive steel panels all around.
'I came across an article from 1981 in an automotive magazine about a Golf Diesel Formula E (a truly ingenious design: it featured start-stop automatic technology and a real economy gearbox where the top speed is reached in 4th gear; 5th gear is for cruising and saving fuel!). It claimed to have a minimum consumption of just 3.9 liters.'
Or a BMW 520 with a tested fuel consumption of 10.5 liters. Today? 12.5 liters! Great progress!
Manufacturers boast that they are investing billions of dollars in the development of new, low-emission engines. So how can it be possible to bring a 1986 Golf 2 with 90 horsepower up to EU3 emissions standards simply by installing a 'secondary air system' that slightly leans out the fuel mixture during the warm-up phase?
Where will it lead when you can buy a Golf that weighs almost 1600 kg (the RS32)? The fifth-generation Golf will definitely surpass that!
Audi sees technological progress as having been achieved when the new A3 weighs only 100 kg more than its predecessor. The drag coefficient didn't even get worse (only the frontal area increased)!
The only hope lies in the legal weight limit of 3.5 tons.

Hello,

hansemann2,5 wrote:

...Or a BMW 520 with a test consumption of 10.5 liters. Today? 12.5 liters! Great progress! The manufacturers boast that they are investing billions of dollars into the development of new engines with lower emissions...

The irony of the increasingly stringent emission standards is that the effort required to meet them is constantly increasing.
Often, lower emission values in areas relevant for exhaust testing have to be achieved at the expense of higher fuel consumption.
The best example is with TDI engines, where the NO _x values are considered. To reduce these values, an exhaust gas recirculation system is installed, and the injection timing is adjusted to be later than it would ideally be for optimal fuel consumption.
You can quickly see a half-liter increase in fuel consumption with the same car.
The energy required for air conditioning, power steering, and the ever-increasing number of electrical components also has to come from somewhere, which further increases consumption.
One reason why cars are becoming increasingly powerful is that people tend to take advantage of the extra power available.
Besides that, switching from a 54 horsepower diesel Golf 2 to a 132 horsepower A3 allowed me to noticeably reduce fuel consumption.
Camper van: 90 km/h (speedometer reading). Golf: 90+ km/h. Audi A3: 90+ km/h.
10 liters per 100 kilometers - 8.5 liters per 100 kilometers.

Highway: 150 km/h (speedometer reading)
Volkswagen Golf - Audi A3
7 l/100km - 6.2 l/100km

With less consumption, you get more driving pleasure, less noise, and air conditioning. You shouldn't be so pessimistic about progress, after all .

Best regards, Rainer.

hansemann2,5 wrote:

The only hope is the legal limit of 3.5 tons.

... now things are getting critical again!
Dere neue EU Führereschein gilt für Fahrzeuge bist 3,5t aber auch Gespanne dürfen ein Zulässiges Gesamtgespanngewicht von 3,5t nicht überschreiten!! Da die Zugfahrzeuge schwerer werden (die WoWas aber auch) wird diese Schwelle bald schon von Mittelklasseautos mit einem kleinen WoWa überschritten -- dann fährst du plötzlich ohne Fahrerlaubnis darum!! SovieReaching the 3.5-ton limit.

Rainer K. wrote:

A prime example of this is the NOx values in TDI engines. To reduce these emissions, an exhaust gas recirculation system is installed, and the injection timing is adjusted to be later than would actually be optimal in terms of fuel consumption. You can quickly see a half-liter increase in fuel consumption with the same car.

... where should I sign this?

The first time I took my new AXR Golf and the caravan out for a drive, I noticed that the fuel consumption was about one liter higher than with my old 1Z. In fact, I even used 11.5 liters per 100 km with the AXR. With the 1Z, I couldn't reach this value even under the most challenging conditions.

Hi,

We once had a sand dune nicknamed '200 D' (referring to the Mercedes-Benz W124 series).
Consumption: 6.5 liters.
I'm currently driving an Audi 100, which is a comparable car in its class.
Consumption: Also 6.5 liters.

Besides the fact that the car was incredibly reliable, the constant crawling speed was extremely annoying. Seriously, on uphill stretches during vacation trips, it would often limit itself to a speed of just under 80 km/h (!).
Considering the Audi's extra power of 43 horsepower and the significantly higher torque of 145 Nm (more than double...), its slightly higher weight, and the fact that you can always travel noticeably faster with the same fuel consumption, I see a small but noticeable improvement here.

Ernst S. wrote:

If it weren't for the fuel consumption and, consequently, the CO2 emissions. Because of that, you should preferably shift to a higher gear, even if you then have to press the accelerator more. -> Therefore, you can't always do everything right.

Hello everyone.

... just now.
Und was ist mir bei Autofahren am nächsten? My wallet.
So, I drive in the highest possible gear, typical for a TDI, at the lowest possible RPM – between 1000 and 1500 RPM – and let it pull when needed.

Because I already pay my environmental tax every year in advance through taxes .