Effects of Jet Tuning (Theories)

Hello.

I once tried to estimate or roughly calculate the effects of swapping injectors in VP 37 engines.
Since the following text may contain errors, I explicitly request corrections, additions, etc., in order to potentially create another specialized article from it (if Rainer deems it appropriate).

Possibly. I am unable to address issues related to inappropriate image content at this time due to a lack of reliable information.


The desired atomization effect during the injection process occurs because the fuel is accelerated to high speeds in the "constrictions" of the nozzle bores, and the jet "breaks up" upon impact with the air.
For example, the total flow area of a 205-degree, 5-hole nozzle is approximately 0.165 mm².
When a 81 kW TDI engine requires a fuel flow rate of approximately 40 mg or about 50 mm³ during an assumed injection duration of 1 millisecond (corresponding to 24 degrees of crankshaft rotation at 4000 rpm), the fuel must be accelerated to approximately 300 m/s through this cross-sectional area.

In reality, several undesirable effects occur: The high pressures, reaching magnitudes of around 1000 bar (?), cause the injection lines to become "swollen" due to their elasticity. The fuel is compressed to a certain extent (!), and leakage losses in the pump and injectors consume a portion of the "geometric" flow rate, which is determined by the pump piston diameter and stroke.

Since the fuel injection pressure required for fuel acceleration increases quadratically with the engine speed (the pressure is used to transfer kinetic energy W = m/2 v² to the fuel, and v is fundamentally proportional to the engine speed), these losses are mainly noticeable in the higher engine speed range.
To compensate for this, the fuel flow must be increased accordingly. This means that the amount of fuel being diverted is further reduced, and the injection duration is essentially extended by the amount of time required for that portion of the fuel that would otherwise not pass through the injectors with the original injection duration.
This relationship between engine speed, throttle valve position, and fuel injection quantity is engine-specific and stored in the pump characteristic map of the electronic diesel control (EDC) system.

The full load correction in the higher RPM range can be observed during a diagnostic test drive using VAGCOM by logging a group of values that includes RPM, fuel injection quantity, and wastegate voltage. While the fuel injection quantity should remain relatively constant from the point where full boost pressure is achieved until the engine begins to limit its power, the wastegate voltage should increase with RPM.



Therefore, if the hole diameter is changed for tuning purposes by, for example, replacing a nozzle from 205 to 216, the total flow area increases to approximately 0.183 square millimeters.
Under otherwise unchanged conditions, the injection speed decreases accordingly to approximately 270 m/s, and the fuel pressure required for fuel acceleration increases quadratically with the speed (or to the fourth power of the hole diameter), reaching approximately 81% of the initial value.

This reduces (in addition to the pressure load on all components involved) the losses described between the delivery volume and the injection quantity, causing the unchanged delivery volume compensation to now be too high. This results in more fuel entering the cylinder, primarily in the higher RPM range, where the aforementioned... Losses occur.

The aforementioned increase in RWG voltage, while the injection quantity remains constant, provides a rough indication of the maximum effect of replacing the standard injectors with "larger" ones. The greater the increase in RWG voltage, the more losses the injection system experiences. The increase in performance achieved solely through nozzle tuning can never be greater than the "lost" amount due to internal losses.

When used in conjunction with electronic tuning without a corresponding increase in boost pressure, larger nozzles can completely deplete the excess air, leading to a significant increase in soot emissions.

In addition, the engine speed is increased until a balance is re-established between the total engine losses and the fuel injection volume.

Since a given amount of fuel now enters the cylinder more quickly, the combustion process tends to concentrate more in the top-dead-center (TDC) area, which generally makes the engine run more harshly, but also tends to improve fuel utilization and can therefore lead to fuel savings.

Unfortunately, the reduced injection pressure results in poorer atomization – roughly equivalent to the engine running at a speed that is lower by an amount corresponding to the ratio of the flow areas (i.e., with the same number of holes, the squared ratio of the hole diameters).
The consequence is poorer emission values, especially in the lower RPM range, which would likely also invalidate the vehicle's operating permit.

Hi Ulf,

I also have a comment on this, after receiving advice from a very helpful Bosch employee:

- in these hydraulic considerations, one must also take into account the length of the nozzle opening, which varies between different nozzles .

I'm currently facing a problem: I have a set of new injectors for my 1Z engine, which have a slightly larger hole diameter but a longer hole. The Bosch employee mentioned that the effects of a change are not easy to calculate. At least, my new injectors are designed for the American 1Z, which has stricter soot emission limits. Therefore, these injectors should produce less soot . However, I don't know what the EDC settings are for vehicles like that. Therefore, I will probably have to try it out and see what happens (although I'm already feeling uncomfortable about it).

Another thing is that I had initially considered replacing the three injectors without NHG with American-made ones, since the NHG injectors are new. However, the Bosch employee strongly advised against installing injectors with different hole diameters or lengths. The resulting vibrations could, for example, severely damage the main bearings of the crankshaft.

Approximately, by how many rpm does the maximum speed increase in your calculation example? That would be important to know for the vehicle inspection.

Hi,
What about the higher injection pressure that the DID 216 injectors have?
The lower fuel flow rate is compensated for by the higher injection pressure, so I would say that the atomization does not become worse.
'I think it will be fine because the 205 injectors also produce a certain amount of pressure, which is more than the 184 injectors, and that means I'll have more fuel in the cylinder.'

The assumption that leakage losses will decrease is correct.

Okay, to reduce the pressure losses in the injection lines, you can also use injection lines with a larger cross-section.

tim27 wrote:

The lower fuel flow rate is compensated for by the higher injection pressure, so I would say that the atomization does not get worse.

Hi Tim,

If we theoretically consider the Bernoulli principle, it means that as the velocity decreases, the pressure head (i.e., the pressure on the wall) inevitably increases (in which case you would be right). The prerequisite for this is that the flow rate supplied by the pump remains constant. However, this increases, which means Ulf is right and the pressure decreases.

tim27 wrote:

Hi, What about the higher injection pressure that the DID 216 injectors have? The lower fuel flow rate is compensated for by the higher injection pressure, so I would say that the atomization does not become worse. Think about it, because it's going to be like this, since the 205 injectors also have a slightly higher pressure than the 184 injectors, and in that case, I'll also have more fuel in the cylinder.

Hi Tim,

You are apparently confusing the opening pressure of the nozzles with the pressure in the system during the injection process (the latter is what I meant in my original post).

"Just imagine connecting the fuel injection line directly to the cylinder – do you really think that hundreds of bar of pressure would build up in the line, even with a nozzle diameter of just a few millimeters, when the fuel can freely escape from the pipe?"

If not, we are fundamentally in agreement: the smaller the injection cross-section, the greater the "back pressure" and, consequently, the higher the pressure - and vice versa.

Quote:

Oh, to reduce the cross-sectional losses in the injection lines, you can also use injection lines with a larger cross-section

.
Aha... and if your spray nozzle on the garden hose is clogged (and therefore not enough water comes out), you buy a thicker hose, attach the same nozzle without cleaning it, and it works again.

-> A chain is only as strong as its weakest link, or was it something else...?

ulf wrote:

Aha... and if your spray nozzle on the garden hose is clogged (and therefore not enough water comes out), you buy a thicker hose, attach the same nozzle without cleaning it, and it works again

Hi Ulf,

Theoretically, he would be correct, as long as the flow rate remains constant (Bernoulli)... I've corrected myself above. However, the flow rate increases significantly, which actually reduces the pressure on the wall.

haehnlein wrote:

theoretically, he would be right, as long as the flow rate is constant (Bernoulli)... I have corrected myself again above. The flow rate increases significantly, so the pressure on the wall actually decreases.

Hi Christian,

I have some slight doubts about whether the Bernoulli principle applies here - I only know it...
1. for gases
2. in practice, as a Venturi nozzle for aircraft airspeed indicators, which creates a vacuum through the acceleration of air in a constricted area.

It is clear that the "transverse pressure" (and thus the suction effect) is lowest where the flow is fastest.

Here, we're talking about using pressure to accelerate the fuel.
And practically every real-world pump builds up the highest pressure when the outflow rate is minimal (or zero).

So, the smaller the nozzle opening, the higher the pressure, and thus the greater the force that accelerates the fuel to increasingly higher speeds (assuming we disregard frictional losses due to surface effects between the nozzle and the fuel).
Or where is the logical flaw in it?

haehnlein wrote:

When considering these hydraulic aspects, it is also necessary to take into account the length of the nozzle opening, which varies between different nozzles . I'm currently facing a problem: I have a set of new injectors for my 1Z engine, and they have a slightly larger hole diameter but a longer hole. The Bosch employee mentioned that the effects of changing them are not easy to calculate. At least, my new injectors are designed for the American 1Z engine, which has stricter particulate emission limits. So, with these nozzles, less soot should be produced . Another thing is that I had initially considered replacing the three injectors without NHG with American-made ones, since the NHG injectors are new. However, the Bosch employee strongly advised against installing injectors with different hole diameters or lengths. The resulting vibrations could, for example, severely damage the main bearings of the crankshaft.

Hi Christian,

This is understandable because the "friction area" between the nozzle and the fuel increases with the hole length, which slows down the fuel flow -> resulting in a lower fuel injection amount.
To compensate, the hole is made larger, which, as described, increases the amount again.

How the injection pattern of a short, narrow channel fundamentally differs from that of a long, larger channel (with the same pressure requirement for a given flow rate) ->

Quote:

By how many rpm, approximately, would the maximum speed increase in your calculation example? That would be important to know for the vehicle inspection (ASU).

Good question - I've asked this several times before, unfortunately without a concrete answer so far .

For every driver who pushes their vehicle to its limits, the moment of truth will inevitably arrive, perhaps sooner rather than later, when they are forced to take time off work due to the consequences. There, his engine is being stressed on the nmax, and if the RPM is too high, he has to come back so many times until it's right - and until then, he's losing the emission test fee each time .
So, I would definitely try it out myself first, just to save money, and then adapt it as needed until it works properly.

I certainly can't say for sure what the effect will be. It definitely also depends on how much the injection quantity is reduced by the EDC in the derating range.

Deleted as requested.

diesel.gustav wrote:

In my experience, it's not the higher RPM range that's critical, but rather the lower RPM range. Because: a lot of fuel, but little combustion air!

Hi diesel.gustav,

that means the consumption is higher in my favorite RPM range .

diesel.gustav wrote:

However: Austrians might be more lenient in this regard. Car repair shops are aware of the problem with exhaust opacity measurements during free acceleration. Currently, we have a 70% diesel share in new vehicles and perhaps around 50% in the existing fleet. Many businesses have occasionally "run into trouble" with customers regarding exhaust opacity measurements and tend to be more cautious in their expert opinions.

We also experience this... at least with my TÜV inspector . He tries to outsmart the measuring device by using the gentlest possible acceleration.. The result: 20 times of revving up .

Deleted as requested.

diesel.gustav wrote:

But that certainly can't be what a serious diesel driver aims for.

I was too hasty again with my new injector set (well, it's not installed yet). What's most important to me is that the car consumes little fuel... it's not a Ferrari. But there's one thing I don't understand: my new injectors are for the American 1Z engine, and the particulate matter emission limits are stricter there. Does that mean that in the full load range, the soot values are actually lower, or does the American 1Z have a different characteristic curve for the ESP ?

haehnlein wrote:

... my new nozzles are for the American 1Z standard, and the particulate matter limits are stricter there.

Hi Christian,

I find it difficult to understand this statement, as diesel fuel in the United States has completely different (and inferior) specifications.
The most significant difference from EU diesel is the sulfur content, which in the US can range from 500 to 1200 ppm (compared to >50 ppm in the EU). This means that the soot emissions of a 1Z TDI in the US (regardless of any other modifications) are likely to be significantly worse. Incidentally, only California has different emission regulations for diesel vehicles, and Volkswagen never officially sold the 1Z engine there. Anyone who wanted a TDI there simply bought it as a temporary registration in a neighboring country, and that was that (the emissions laws only apply to the initial registration ).
I think it's more likely that the other injectors are related to the significantly lower cetane number of 42-45 for US diesel (compared to 49 for EU diesel). The US diesel engine is significantly less responsive and will certainly not perform as well as the TDI without modifications.
The poor quality of diesel fuel is also the reason why there are (still) no PD TDIs in the USA. Consequently, the number of CDIs is also very low in the USA. And the diesel particulate filter isn't really an issue in the US anyway, because of the poor fuel quality (it only works with low-sulfur diesel).

[quote="Bertil"] I find it difficult to understand this statement, as diesel fuel in the United States has completely different (worse) specifications. [quote]

Hi Bertil,

"...which is what the friendly Bosch employee told me."

Quote:

The poor quality of diesel is also the reason why there are (still) no PD TDIs in the USA.

I don't think so (there was a program about it recently): The image of diesel is terrible in the USA (and the price compared to gasoline), and besides, the Americans have secured a substantial amount of fuel for the next few decades ...so there won't be any Plug-in Diesels there in ten years.

My nozzles are also still suitable for the German AEY... what do you think... should I just install them (I think the cross-sectional differences are 0.164 old and 0.174 new) or should I sell them ?

Hi Christian,

haehnlein wrote:

"...which is what the friendly Bosch employee told me."

He really went fishing in murky waters .

Quote:

I don't think so (there was a program about it recently): The image of diesel is terrible in the US (and the price compared to gasoline)...

You're right...

Quote:

... and furthermore, the Americans have secured a substantial amount of fuel for the next few decades .

That's not true! The estimated oil reserves are only enough for approximately 25-30 years worldwide! I don't think it's possible for the US to secure reserves for several decades now. The "emergency reserve" of the United States is estimated to last only 6-12 months (and applies only to military and government vehicles)!

Quote:

...then there won't be any PDs (presumably referring to "Personal Doctors" or a similar term) there in ten years.

For about five years, efforts have been made in the United States to bring diesel standards up to the EU level, but this project suffered a major setback with the presidency of George W. Bush, and the US standard remains in place. This secures a certain monopoly position for US automakers in the diesel market. European diesel engines (PD-TDI and CDI or HDI-FAP) absolutely require the (low-sulfur and high-cetane) EU diesel fuel!
If you visit the VWoA website, you'll notice that they still list the 90 hp VP37 TDI engine! And that's from the year 2003! In Europe, the VP37 engines were discontinued by VW as early as May 2002!

Quote:

-- On page 4, you can see the different engine variants. My nozzles are also still suitable for the German AEY... what do you think... should I just install them (I think the cross-sectional differences are 0.164 old and 0.174 new) or continue to sell them

http://www.vw.com/Brochure/pdfs/jetta.pdf?

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