Effekte bei Düsentuning (Theorien) | Posts 16+

Hi,

There are great discussions about the TDIs and the bad reputation of diesel engines in the US at [link/platform].
http://www.tdiclub.com

Okay, ich bin bereit. Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.

http://forums.tdiclub.com/showflat.php?Cat=&Board=UBB5&Number=169842&Forum=All_Forums&Words=diesel%20quality&Match=Entire%20Phrase&Searchpage=1&Limit=25&Old=allposts&Main=169842&Search=true#Post169842

By the way, US diesel only has a cetane rating of 40. This poses significant challenges for common rail and pump-injector systems.

Hi,

ulf wrote:

I have some slight doubts about whether the Bernoulli principle is applicable here - I only know...

The Bernoulli's principle applies everywhere, whether it's a gas or a liquid. Applicable to all flow phenomena, whether involving wings or propellers.
However, it only represents a simplified form of the equation: it does not include friction losses or geodetic height.
Friction will be more than sufficient in the narrow nozzles.
A stream of liquid in air breaks up into droplets for three reasons:
1. Surface tension (not relevant here).
2. Friction with air.
3. Internal turbulence, generated in the nozzle (this is where the precisely defined nozzle shape comes into play, as it also influences the flow).

Bertil wrote:

The estimated reserves of crude oil are only enough for approximately 25-30 years, and that's worldwide!

Hi Bertil,

Yes, yes, this has been said before, even 40 years ago: 1. For example, further enormous oil reserves are still suspected in Iraq. 2. Are there vast reserves of crude oil of lower quality, the processing of which only becomes worthwhile at a certain crude oil price , but now enough OT, otherwise Ulf will be annoyed that we are derailing his topic with off-topic comments .

Quote:

I would definitely give it a try, but you should be very careful and closely monitor the engine.

I'm not sure if I want to spend the €290 for the "guinea pig" function (that's how much the nozzle set with two NHGs cost).

diesel.gustav wrote:

I would have been interested to know why you believe that the charging rate should be increased.

Hi Gustav,

As far as I understand the underlying processes:

"Abregeldrehzahl" refers to the engine speed at which the energy supplied by the diesel fuel is balanced by all the engine losses (heat, noise, friction, etc.).

If more diesel fuel is injected (through larger injector holes), this can also lead to increased losses -> the engine speed increases until a new equilibrium state is reached.

Now, the amount of fuel injected is reduced towards zero by the EDC (Electronic Diesel Control) at some point above the rated speed, and this reduction increases with increasing engine speed.
But, as far as I know, this doesn't happen with an "infinite steepness" (meaning, for example, 4999.99 rpm = 20 mg, 5000 rpm = 0 mg/stroke - in which case, it would definitely be a radical change at 5000 rpm), but rather gradually.

Therefore, if more diesel fuel is injected into the cylinders and the engine runs at a higher speed, the increase in engine speed is not only limited by the increasing losses, but also by the further reduction in the fuel delivery volume.

However, there will likely be an increase in RPM – perhaps only a slight increase, for example, 10 RPM, or perhaps as much as 300 RPM – and I cannot rule out either possibility due to a lack of practical experience.
The effect likely also depends on the percentage increase in the injection port size.

Quote:

Larger misfires are detected during the vehicle inspection (if the emissions test in your country is similar to the § 57 inspection we have in Austria) due to the increased exhaust opacity during free acceleration. Based on my experience, the critical range is not the upper, but the lower RPM range. Because: a lot of fuel, but little combustion air!

However, I don't think this should be too critical, because at low speeds, the pump still delivers fuel relatively "slowly," so even the standard injectors will hardly be able to hold back any diesel.
And only this "swallowing amount" can, through larger nozzles, additionally enter the combustion chamber - an effect that only becomes significant at higher revolutions per minute = flow rates .

Due to the lower "back pressure" in larger nozzles, the atomization is naturally worse at every speed compared to the standard nozzles. I consider that to be more critical with regard to the soot values.


I'm glad that a (in my opinion) relatively well-informed discussion about this topic is finally starting.

As far as I understand the underlying processes:

'Abregeldrehzahl' refers to the engine speed at which the energy supplied by the diesel fuel is balanced by all the engine losses (heat, noise, friction, etc.).

If more diesel fuel is injected (through larger injector holes), this can also lead to increased losses -> the engine speed increases until a new equilibrium state is reached.

Now, the amount of fuel injected is reduced towards zero by the EDC (Electronic Diesel Control) at some point above the rated speed, and this reduction increases with increasing engine speed.
But, as far as I know, this doesn't happen with an 'infinite steepness' (meaning, for example, 4999.99 rpm = 20 mg, 5000 rpm = 0 mg/stroke - in which case, it would definitely be a radical change at 5000 rpm), but rather gradually.




counterargument: ALH and ASV have the same pump, but only different nozzles.

and take a look here: even the mechanical pumps are regulated quite strictly. This is necessary because otherwise the machine would destroy itself.

[img][/img]

I don't think there will be any problems with that.

CU Gremlin.http://www.ralfhandel.de/reglerkennlinien.jpg{MARKER}

Gremlin wrote:

counterargument: ALH and ASV have the same pump, but only different nozzles.

Hi Ralf,

"That's not a counter-argument for me: in the pump characteristic curve, the nozzle properties are somehow 'mixed up'."
Since the ALH and ASV likely have different engine control units, the respective pump characteristic curves are simply stored in them.
In other words, at the target engine speed of 5000 RPM, the ALH pump is controlled differently, so that the differences between the injectors are ultimately compensated for.

Quote:

and take a look here: even the mechanical pumps are regulated quite strictly.

This is necessary because otherwise the machine would tear itself apart...

It's clear already, but it's not infinitely steep either.
I maintain that: any excess diesel in the cylinder within the range of the cut-off speed will, in principle, lead to higher engine speeds until a "new" equilibrium is reached between the (further or re-)cut-off amount and the increased engine losses .

The actual difference in the new rotational speed remains, apparently, a mystery.

Hi,
It depends on how the EDS actually works. The diagrams of the mechanical ESP systems suggest a proportional control system. If the EDS system works the same way, then you're probably right.
However, there are also integrating controllers that achieve the desired value without any deviation. Example: Cruise control.
(I don't have one myself, but I think that's how it works there.)
Proportional controllers are relatively inexpensive and easy to manufacture mechanically, and they offer a fast response time. Integral controllers, on the other hand, are more expensive and have a slower response. Proportional-integral controllers are better. However, this shouldn't be such a big factor when it comes to electronics.
Perhaps someone knows the necessary details.

Okay, I say: the maximum speed is completely independent of the nozzles.

reason:

We have a fully electronic diesel control (EDC) system.
'If you set the 'Vmax' to 5000, it will do that, regardless of the injectors used. With larger injectors, the engine will produce more torque and reach 'Vmax' more easily, potentially resulting in a larger over-rev (or even triggering one). However, the maximum RPM will be rigidly set to 5000.'

In the mechanical regulator, the speed may increase slightly, within the range of 4.

P-I-D control functions can be implemented perfectly easily using software. Mechanical controllers, of course, have problems in this area. The 'gentle' settling behavior at increasing speed suggests that the goal is to avoid overshoot. Ultimately, the D-component must not be too high for perfect regulation. Larger nozzles can interfere with this. However, the P-I component will definitely bring the speed back to the desired value.

I'd like to try it out, who can give me a set of nozzles?

CU Gremlin.

Deleted as requested.

christians wrote:

There are no frictional losses and no geodetic height.

Hi Christian,

"No, there's also a Bernoulli equation with losses . Even for unsteady conditions (dQ/dt is not equal to zero, with Q=dV/dt -> volumetric flow rate = mass flow rate if incompressible), which are present in this comparison (small hole vs. large hole)."

Unfortunately, I know far too little about fuel injection pumps, so at this point, I'm at a dead end . First, you need to figure out exactly how the volumetric flow changes due to the change in the cross-sectional area .

Gremlin wrote:

I'd like to try it out, who can give me a set of nozzles?

Hi Gremlin,

...someone wants me to feel addressed with my "nozzle set" with 2 NHG .

diesel.gustav wrote:

When applying the injection system to the engine, everything is meticulously adjusted. This vote is doomed if we simply install different nozzles now

.

Hello Gustav.

Basically, you're right, but in my opinion, we should still try to differentiate "how far away from hell" – as long as the spray patterns are compatible with the foreign pistons, which I'm just speculatively assuming for now.

Replacement of the standard 81 kW injectors with 205 micron nozzle holes with T4 injectors with 216 micron nozzle holes.
The engines have a cylinder power output of 20 kW or 22 kW. In general, this "disturbance" is likely to be on the order of "only" 10%, which also corresponds to the ratio of the hole cross-sections.

Example: The ALH (manual transmission) and ASV models are both classified as EU3 compliant and share the same pump, but have different injectors.
This implies that the injection hydraulics of the ALH engine are fundamentally compatible with the 81 kW ASV injectors and can meet EU3 standards. Therefore, replacing the injectors on an ALH engine might only cause issues due to potentially "incorrect" injection timings (which are controlled by the 66 kW engine control unit) or injection volumes that are not intended for the 81 kW engine.

Even further increasing the injector size to 216s should, from this perspective, not have catastrophic consequences, but at worst, the system would perform like a normal 81 kW engine, with an increase of approximately 10%, possibly more. Spraying problems can be frustrating.

However, it's different for the 1Z/AHU/AFN/AHF generation: these engines have 3 different pumps, so even the 81 kW injectors on the 66 kW engine, due to the significantly larger hole diameter (21% larger), are likely to produce relatively unpredictable results – and of course, even more so with 216 injectors instead of 184 injectors on the 66 kW engine.

AFAIK, the hole size is always a compromise between good emission values and low fuel consumption, especially at lower engine speeds (-> smaller holes), and sufficient flow for high peak power at higher speeds (-> larger holes).
In other words, strictly speaking, there is probably an optimal hole size for each speed (in VP engines), so ideally, the hole sizes would be adjustable depending on the speed.

And with moderately(!) larger nozzles of the same basic design, I believe one essentially only shifts the aforementioned overall compromise regarding hole sizes somewhat towards higher RPMs and more power, at the expense of "slightly" worse fuel consumption and emissions in the lower RPM range... or am I fundamentally wrong about that?


To estimate the higher revving speed, I finally found a torque curve for the AFN engine that PP had emailed to me some time ago.
The maximum possible fuel injection amount is 31 mg at 4473 rpm, and it is zero at 5355 rpm.

Assuming a linear fuel cut-off between 4473 and 5355 rpm, fuel injection still occurs above the redline limit of 5200 rpm (and even more so above the "ideal" value of 5000 rpm).
At 5000 rpm, it would be approximately 13 mg per kilowatt-hour.

Assuming a further increase in injection volume by 10% in the upper RPM range due to the use of 216 injectors, the initial injection amount at 5000 rpm would be 14.3 mg.
That means the engine will continue to rev up until only 13 mg of fuel are injected again, which means a reduction of 1.3 mg.

These 1.3 mg correspond to a speed variation of (5355 - 4473) / 31 x 1.3 = approximately 37 rpm, which is the amount by which the IMO's rated speed is likely to increase.
While this isn't much (in this highly simplified calculation, for example, without considering further increasing motor losses), it's still more than nothing.

Okay, now the colleagues with the "nothing is happening" viewpoint are trying to contradict me again .

Hello everyone!



The mere presence of a mean and a maximum value already suggests that the EDC cannot precisely regulate at a certain speed. Otherwise, wouldn't every TDI engine (except those with modified rev limiter settings) show exactly 5000 RPM? (But that's not the case, is it?) As Ulf describes the control process (where the injection amount decreases with RPM), there will always be a slightly different RPM, depending on the losses.

How much do the losses in fuel injection change due to an increase in nozzle size?

It makes sense that nozzles designed for higher performance would likely also deliver more power in a less powerful engine. But I suppose it's not so easy to calculate.


The example calculation at the beginning, which states that 81% more pump pressure is needed to achieve the same volumetric flow rate, only applies to laminar, incompressible, steady, and lossless pipe flows.

Hopefully, the flow is still laminar (does anyone know the viscosity of diesel?). It's probably not entirely incompressible at 1000 bar, I think. Unfortunately, the flow is not stationary at all. I have a script that shows the propagation of pressure waves in the lines... The pressure doesn't spread out immediately; it takes some time for it to propagate from the pump to the nozzle at the speed of sound. The pressure wave is then reflected there... I'll stop there, but the injection quantity is definitely not constant over time. And the pressure that builds up depends on the size of the outlet, which makes it difficult to calculate. It also makes a big difference how the cross-sectional area is distributed across the number of holes (especially regarding flow losses – so, the losses due to roughness are probably disproportionately high with smaller holes).
The formula Ulf used to calculate the 81% (I have no idea how he came up with that without a fluid dynamics textbook).
Volume of subsidized fuel = Pi * Radius^4 * (p1 - p2) * t / (my * Length) [Hagen-Poiseuille equation]
It will not yet produce a satisfactory result, due to the circumstances mentioned above. I believe such things are never actually calculated, but always tested on a pump test bench.

If anyone is testing larger nozzles, please measure and record the flow time before and after the test.

Best regards.
Ernst.

Ernst S. wrote:

The mere presence of a mean and a maximum value already suggests that the EDC cannot precisely regulate at a certain engine speed. Otherwise, in every TDI (except those with speed-limited tuning), exactly 5000 RPM would be measured. (But that's not the case, is it?)

As Ulf describes the regulation process (the injection amount decreases with engine speed), there will always be a slightly different engine speed, depending on the losses.


Hi Ernst,

So, you still exist

Quote:

. The recommended operating speed range is even 4800 to 5200 rpm. The middle of it is exactly 5000...

So, the idea that injectors designed for higher performance will likely deliver more power even in a weaker engine sounds reasonable. But I suppose it's not so easy to calculate that.

Quote:

That's not what I meant to express – at least not as a precise prediction, but rather as a rough estimate. However, the proportionality between the maximum cylinder power of the different engines (16.5 / 20.25 / 22.2 kW) and the injection cross-sections of the respective injectors (simply squared hole diameters: 0.034 / 0.042 / 0.047 mm²) is quite remarkable – except for the automatic ALH, which probably already operates at about half the common rail pressure level...?

The formula that Ulf used to calculate the 81% (I have no idea how he came up with that without a fluid mechanics textbook). .

I assumed the necessary amount of work required for acceleration.
To achieve the same diesel output in the same amount of time with a cross-sectional area that is halved, the velocity must be doubled.
According to the formula W = m/2 * v², four times the energy is required, which must be supplied through pressure. Therefore, four times the pressure is necessary.
Alternatively, with a 10% larger cross-section: 0.9 times the speed -> 0.81 times the pressure.

Hi,

If it helps... following the "AU" (vehicle inspection) report that I have here (from when the workshop tried to convince me that the car was not emitting excessive fumes), the following:

Idle speed min: 5043 according to vehicle data (I have no idea where they got that from), tolerance is, as Ulf said, 4800-5200.

And below are the results of the three high-revving tests: 5073, 5082, and 5053.

The initial speed was exactly 905 (idle speed) each time, which indicates that the control unit can maintain this perfectly, but the other one doesn't quite achieve it.

The engine, as indicated in the signature, is an ASV.

Best regards,

Jan.

Jan6K wrote:

Abregeldrehzahl min: 5043 (according to vehicle data, I have no idea where this information comes from). to read it out) . . .

Hi again.

During my vehicle inspection (TÜV), the engine speed is measured at the battery (!!) by analyzing the sine wave remnants of the rectified charging voltage.

For this, the translation of "Motor-Lima" (pulley diameter) must be known, as well as the magnetic structure of the alternator (number of poles and related details).
That is to say, using the wrong bra could potentially drive the TÜV inspectors crazy – especially if they don't have an alternative measurement method.

Most likely, VP-TDIs fall within a range of +/- 30 percent of the tolerance around the mean value.