Warum sind PDs obenraus so "lahm"? | Posts 48+

WarLord wrote:

Hm, don't BMW and DC use larger chargers for their engines? That's why they supposedly have such a powerful low-end and pull hard at the top. And then there's the drivetrain: front-wheel drive is just for cheapskates. Greetings, WarLord

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To my knowledge, at least DC uses the same chargers as VW. But we shouldn't forget that a BMW 6-cylinder is still something completely different from a 4-cylinder PD engine! It's perfectly clear that such an engine has a different power characteristic. Also, I can't say that BMW or Mercedes diesels have a "hole" in their power delivery. (I've driven a 330d and an E270 CDI). I find that PD engines tend to develop their power in a less harmonious way from the bottom end, and you're more likely to experience a sudden surge of power there, compared to the overall power output of the engine.

Hello everyone,

Quote from Thomas:
It essentially means that the gear ratio is simply a compromise between the impeller speed and the maximum Yes, the turbocharger speed indirectly indicates the possible airflow, and even a PD injection system reaches its limits in the upper range, especially with regard to exhaust emissions.
Quote from Thomas:
But why only with the PDs? Does the same apply to VEP-TDI models?
The VNT15 likely has a lower maximum permissible rotational speed than the GT17. For those, there should also be a noticeable 'weak' upper RPM range in relation to the 'agile' lower RPM range.
With the good old AFN engine, this difference isn't as noticeable during normal driving. However, the increase from 235 Nm to 310 Nm in the mid-range is a significant difference. In the higher range, however, the AFN engine with 81 kW and the AJM engine with 85 kW offer only marginal improvements.
Quote from Thomas:
Looking back at the development of TDI engines, the injectors (ATL) are becoming smaller and 'weaker.' Consequently, the power output is also decreasing, which in turn reduces the fuel injection volume. But this phenomenon seems to be solely due to the injection technology?
The requirements for the development of the PDs (presumably referring to a specific type of device) regarding ATL technology were improved responsiveness (keyword: rotating masses) and increased pressure in the lower range. This was achieved by using 'smaller' ATL units. As a result, the operating range of the ATLs shifts more towards the lower engine speed range. However, the challenge was to maintain or even increase the performance in the upper range. However, the key point is that, despite further development, this has also brought us closer to the performance limits of the ATL, especially with the ATL's rotational speed.
The transition from VEP to PD technology allowed for a larger amount of fuel to be injected more quickly and finely atomized, which not only resulted in increased power but also significantly improved exhaust emissions, essentially achieving EURO 4 standards without a particulate filter. With VEP systems, EURO 2 or 3 was the limit. However, the future lies with Common Rail technology, which can already achieve pressures of up to 1800 bar with an almost ideal injection process. Adding a 4-valve design further pushes the limits of what's possible, with turbocharging technology becoming the limiting factor. Not quite, a two-stage charging process might be the key.

Below, I have listed the speed limits for a turbocharged 1.9 DI engine (without considering emissions performance). I hope this makes things clearer.

Speed range.
1000 - 1500 revolutions per minute.
Limit by:
max. The filling is determined by the compressor's pressure limit.
(The engine could handle more boost pressure, but the ATL...)
(currently, it cannot achieve the required pressure with small production runs).

Speed range.
1500 - 3000 revolutions per minute.
Limit by:
Combustion pressure, the peak pressure that determines the mechanical stress on the pistons/cylinder and crankshaft (maximum 150 bar for the AFN VP-TDI and maximum 170 bar for the PD-TDI). Within this RPM range, both the ATL system and the fuel injection system can always provide sufficient air/fuel mass, and the only limiting factor is the strength of the engine components.

Speed range.
3000 - 4500 revolutions per minute.
Limit by:
Restriction of the intake manifold (even an intake valve with a swirl channel eventually reaches its limit) and/or reaching the maximum permissible engine speed, which also limits the possible fuel injection amount. If there is a lack of air (incomplete combustion due to oxygen deficiency), soot will form, and the exhaust temperature will rise. To avoid forgetting the old diesel problem of high engine speeds, at 4000 RPM, 1.9 milliseconds (45° crank angle) is simply not a very long time for proper air-fuel mixing and combustion.

Best regards.
from Sepp

Sepp wrote:

.... In the case of VEPs, the limit was reached with EURO 2 or 3. ...

Well then, AUDI must have done something terribly wrong: EURO 4 with the VP44 and without a DPF on the V6 TDI!
You can't really say that in general terms.

Quote:

However, the future is CommonRail, where pressures of up to 1800 bar are already possible with an almost ideal injection process.

... 1800 bar with (currently) uncontrollable vibrations on the rail (which is exactly the problem that PD avoids) and issues related to meeting EU4 standards without a DPF. Currently, there is only one CR diesel engine that complies with the EU4 standard without a DPF, and that is the Opel lean-burn diesel (1.7 CDTI 16V with 80 hp and 170 Nm).

Quote:

Add 4-valve technology to it, and suddenly, forced induction becomes the limit of what's possible.

Am I mistaken, or do the new VW PD engines also have 4-valve cylinder heads? Unfortunately, the advantage of CR regarding its compact design and the resulting use of 4V cylinder heads is no longer present.

Quote:

Not quite, two-stage charging could be the magic word.

That's where the problem lies.

The 8V PD engines are unable to draw in enough air at higher RPMs to fully realize their potential. At least, not with conventional turbocharging technology (see above). (Post by Sepp).
"Anyone who has driven the new 16V PD engine can understand what it means to ensure that the cylinders are adequately supplied with fresh air at high engine speeds." With these engines, there's no feeling of sluggishness in the higher RPM range.

The manufacturers of NKW engines also faced problems with poor air supply when introducing the PLD system (e.g., Mercedes Actros). The "problem" could only be resolved after optimizing the intake and exhaust pathways. Fortunately, due to space constraints, 4-valve cylinder heads could be used in commercial vehicles relatively early on, which meant that the problem of insufficient fresh air was not as severe.

Hello Sepp,

Quote:

With the good old AFN, this doesn't stand out as much during normal driving. 235 Nm to 310 Nm in the mid-range is already a significant difference. In the higher range, an AFN engine with 81 kW and an AJM engine with 85 kW offer only slightly more power. "Quote

"

This sluggishness also occurs in the AFN engine, but it is nowhere near as pronounced as it is in the "highly-bred" PD TDI engines like the ASZ/ARL.

Quote:

However, the future is CommonRail, where pressures of up to 1800 bar are already possible with an almost ideal injection process

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1800 bar is about 200 bar less than what the PD injectors are currently capable of, and I've always thought that VW engineers could never have enough pressure.

My understanding so far has been that CR (Common Rail) allows for a smoother engine running due to constant pressure, but it comes with more drawbacks than the pump-injector technology.

Quote:

Speed range. 1000 - 1500 revolutions per minute (RPM). Limited by: max. The filling level is determined by the compressor's pressure limit. (The engine could handle more boost pressure, but the ATL...) (currently, it cannot achieve the required pressure with small production runs).

Then the ideal solution would be a mechanical supercharger for the lower RPM range and a bypass valve for the upper RPM range. This would allow us to avoid the complex and expensive variable turbine geometry (VTG) system and instead benefit from the lighter operation of the ATL (turbocharger) with a wastegate. The entire process needs to be redirected through a kind of "switching duct" so that the turbocharger doesn't draw air from the compressor.

Thus, the air supply would be secured, and we would only need to deal with the mechanical stress limits of the components.

Ultimately, this is just a calculation, a comparison of costs and benefits.

I could also imagine getting by with just a wastegate turbocharger. Development never stands still, who knows what kind of turbochargers we'll have in a few years.
Ceramic bearings, lighter shafts...

Quote:

Speed range. 3000 - 4500 revolutions per minute (RPM). Limited by: Restriction of the intake manifold (even an intake valve with a swirl channel eventually reaches its limit) and/or the maximum permissible engine speed is reached, which also limits the possible fuel injection amount. If there is a lack of air (incomplete combustion due to oxygen deficiency), there will be soot, and the exhaust temperature will rise. To avoid forgetting the old diesel problem of high engine speeds, at 4000 RPM, 1.9 milliseconds (45° crank angle) is simply not a very long time for proper air-fuel mixing and combustion.

I think that here, you can't have enough injection pressure, and actually, large injector nozzle holes should also be disadvantageous when considering soot and exhaust emissions. Shouldn't we also increase the size of the channels leading to the valves in mass production, as long as it's cost-effective? This would at least raise the flow limit. Larger turbochargers aren't the problem; it's the response time.
Hmmm...

Actually, you've described exactly the problems that one should consider when doing diesel tuning, and that's also the answer to Ulf's question.

Quote:

... 1800 bar with (currently) uncontrollable vibrations on the rail (which is exactly the problem that PD avoids) and issues that prevent the EU4 standard from being met without a DPF. Currently, there is only one CR diesel engine that complies with the EU4 standard without a DPF, and that is the Opel lean-burn diesel (1.7 CDTI 16V with 80 hp and 170 Nm).

I once read that the main reason for using common rail systems is cost, and if I remember correctly, even higher pressures than 2050 bar are desired, and common rail technology isn't yet capable of handling those pressures.

Greetings.
Thomas.

Thomas wrote:

...I once read that the main reason for using Common Rail systems is cost, and if I remember correctly, even higher pressures than 2050 bar are desired, and CR systems don't yet handle that.

That's exactly right.
For a CR (Common Rail) engine, you only need a slightly modified cylinder head, while the PD (Pump Duse) cylinder head often has to be a relatively expensive custom-made part. However, once you've gone beyond the point of having to have a PD diesel head custom-made (like VW did), the cost factor shouldn't be a problem anymore. In return, with a PD system, you get a better efficiency, better emissions due to cleaner combustion, and more power/torque. The common rail (CR) and positive displacement (PD) systems are likely to be priced at a similar level, considering only the pump and injector unit itself.

Hello,

@Bertil
At that time, I think the decision to use the VP44 was not wrong, but from today's perspective, Audi had a good reason to switch to common rail (CR) and a timing chain in the new 3.0 V6 engine. The key advantage of CR (third generation) compared to PD is the ability to represent the ideal injection process more accurately, and that could be more important than 200 bar more injection pressure. Of course, cost factors are also a very important consideration, especially with 6-cylinder engines. It will be interesting to see if my prediction also applies to the 4-cylinder VW TDI engines one day.
@Thomas
'That sounds good, the combination of a mechanically driven supercharger at low RPM and a valve-driven supercharger in the mid and upper RPM range. TTS-Performance offers a mechanically driven supercharger (a simple design with a ribbed belt drive).' Such a project would definitely be fun.

Best regards from Sepp.

Sepp wrote:

... The key point is that CR (third generation) technology, unlike PD, allows for a better representation of the ideal injection process...

The days of [something] are soon to be over with the upcoming Piezo PD.

Quote:

But of course, cost considerations are also a very important factor, especially with 6 cylinders.

A PD 6-cylinder engine was not possible with EDC15 (the maximum was 5 cylinders, which is why the V10 is a double 5-cylinder), but with the "new" generation of EDC16, a 6-cylinder engine should also be possible (let's hope for the best). Therefore, the decision to use a CR (common rail) system was also made for the 3.0 V6 TDI engine.

Quote:

It will be interesting to see, and we'll see if my prediction also applies to the 4-cylinder VW TDI engines one day.

First, the development of the 16V PD head needs to pay for itself, and that will likely take several years. Furthermore, Siemens VDO plans to revolutionize the PD system once again with piezo PD elements.

Hi,
Work is also being done on ATL vehicles with electric auxiliary drives.

Hi Sepp,

I just saw some T3 and T4 turbochargers with ceramic bearings from DRV-berlin, which supposedly spool up at the lowest exhaust gas volume and "relatively" respond quickly. Of course, a T3 or T4 turbocharger is too large, but if we can apply the technology to our smaller turbocharger, who knows, maybe we can then do without a variable geometry turbine (VTG) or mechanical supercharging?

Unfortunately, the addition of another component to the serpentine belt and the complex air ducting don't make things any easier. But for now, there is still plenty to do, and today is not the end of the world .

@ Christian

Do you mean an electric motor that increases or maintains the speed of the ATL (presumably referring to a turbocharger) when the exhaust gas flow is insufficient, or are you referring to this electric VTG (Variable Turbine Geometry) adjustment?

@Bertil

Piezo PD elements should already exist. I just don't know in which vehicle they are installed. Which other companies, besides VAG, still use the PD (Pumpe-Düse) technology?

However, I am almost certain that the system with the highest pressure will not be implemented due to the emission regulations. Aside from the particle thing...

Greetings.
Thomas.

Hi,
This is a type of electric motor that is integrated into the loader shaft. An electric adjustment motor, including feedback to the control unit, meaning a true servo drive, would certainly make troubleshooting easier if the VTG (variable geometry turbocharger) jams again.
What does the storage material have to do with this? Does the oil adhere to it better than to metal, thereby enabling higher speeds? I'm not really sure I believe that.

Hi Thomas,

Thomas wrote:

Piezo PD elements should already exist. I just don't know which vehicle they are installed in.

Not yet in a production vehicle... so far, only in test vehicles. As far as I recall, the plan was to start mass production by the end of 2004.

Quote:

Besides VAG, which other manufacturers still use the PD (pump-injector) technology?

Land Rover, and even before VW! More are waiting in the wings.
And when it comes to trucks, virtually all the major manufacturers are represented, starting with DC...

Quote:

I am almost certain that the system with the highest pressure will be implemented because of the emission limits. Aside from the particle thing...

The DPF (Diesel Particulate Filter) makes the CR (Common Rail) system competitive again in the emissions discussion (compared to the PD - Pumpe-Düse - system). The shortcomings of the CR system in terms of soot emissions can be compensated for by the DPF. However, I doubt that this will make things cheaper. It might be beneficial for the manufacturer, but not for the customer. The DPF (Diesel Particulate Filter) certainly means increased fuel consumption and/or reduced performance.
I hope that the better system (in terms of emissions) will prevail, and not the cheapest one. But unfortunately, that's the reality of the market today. Greed is good... even at the expense of the environment... whatever... .
In the 1980s, it wasn't the then-best video system (V2000), but the cheapest one (VHS) that ultimately prevailed.

Hello,

@Thomas
I believe this will be a major direction in the further development of small ATL (Automatic Transmission Lines). Storage still holds significant potential here, especially for non-stationary applications. Initially, one often thinks of radial bearings, but the actual weak point is the thrust bearing. If it's possible to reduce power loss here, for example, by using ceramic bearings, while still maintaining good wear resistance in the handle, then a flap-type air turbine lifter could once again become a viable option.
The second factor is the rotating mass of the runner. Since the turbine wheels are made of a 'heavy' nickel alloy, simply using a lighter material offers significant advantages (Mitsubishi has already demonstrated this). Here, VTG (Variable Turbine Geometry) generally has a disadvantage compared to the variable geometry turbocharger (VG turbocharger) due to the 'large' geometry of the turbine wheel.
@Bertil
I often work with VW PD engines and I also appreciate this injection system, as it has clear advantages over the CR system. But when I see how the CR (compressed representation) initiative is now being pushed forward and how everyone is getting on board except for VW, I'm simply curious to see how long VW's PD (presumably a competing technology) will last.

Best regards from Sepp.

Hello everyone!
As a small addition regarding the use of injection systems in the non-road mobile machinery sector, as the question was raised earlier.
'True' PD (Pump Denoise) systems, according to my latest information, are only used by Volvo and Scania, and Scania only uses them in their 6-cylinder engines with a displacement of up to 12 liters; the larger V8 engines use PLD (Pump Level Denoise) instead.
MB also also uses PLD systems in the Actros, but it's not surprising since only V-engines are used.
MAN has opted for CR (Common Rail) technology in its latest engine development for commercial vehicles. I don't know if they've finally reached the level of performance that's advertised on the door.
DAF also uses common rail direct injection (CRDI), and it's quite evident in their engines that they essentially replaced the inline pump with a CRDI pump assembly.

Actually, when these new injection systems emerged in the early/mid-90s, common-rail direct injection (CRDI) had certain disadvantages compared to pre-chamber injection (PLDI) due to the relatively short injection line. This was because it wasn't possible to operate at quite as high a pressure, as the line proved to be a weak point or expanded slightly under the sometimes extreme pressure peaks, resulting in a certain amount of pressure loss. Is that still the case?

Regards,

Dominique.

MAN has recently switched to CR in the latest engine upgrade for the TGA. I don't know if they have finally reached the level of performance that is stated on the door.

They must be here, otherwise our driver would have complained by now.
Special permit for a semi-trailer (construction waste recycling plant).

The things just sound incredibly awful when starting up .

CU Gremlin.

Hello,

In the field of commercial vehicle engines, IVECO is a current example of the highly successful use of the 'true' PD system, for example, in the CURSOR8, an 8-liter, 6-cylinder inline engine with 350 horsepower. Notably, it was the first engine in the pure commercial vehicle segment to feature a variable geometry turbocharger (VTG) in series production.

Greetings.

D. Kurz wrote:

So, when these new injection systems emerged in the early/mid-90s, there were certain disadvantages to PD compared to PLD, due to the relatively short injection line. This was because it wasn't possible to operate at quite as high a pressure, as the line proved to be a weak point or, in some cases, expanded slightly under the extreme pressure peaks, resulting in a certain amount of pressure loss. Is that still the case?

Hi,

You will always experience some pressure loss in a pipeline. That's why PD (Pressure Dielectric) technology evolved from PLD (Plasma Light Dielectric) to save space and eliminate the troublesome pipeline. The pipeline remains a "problem," but modern techniques have largely overcome this issue. PD/PLD systems in nuclear fusion facilities are operating reliably. You can get a relatively high amount of torque even with relatively small engines.
The operating principle of PD and PLD is almost identical. Since NFZ engines are not as sensitive to displacement as our "toy engines," but rather rely more on the amount of fuel used, they predominantly use PLD (presumably referring to a specific type of fuel or fuel system).
Bosch refers to PD (positive displacement) and PLD (positive displacement leveling device) in the same breath (UIP = Unit Injector Pump... regardless of whether it's a common rail or not).