Jet Tuning: Expert Articles & Guides

Hello.

Based on recent discussions in this forum and my own experiences, I've written something about "nozzle swap" tuning.
Rainer has published it as a new article online.

"Anyone who finds errors in this (especially the injection molding experts!) or has suggestions for improvements/additions is welcome to share them so that the article can be adjusted accordingly."

Subject: Venting.

We always leave the connections at the nozzles slightly loose until a reasonable amount of diesel has flowed through, and then we tighten them.
It's working well...
and complies with Bosch guidelines .

CU Gremlin.

Gremlin wrote:

We always leave the connections at the nozzles slightly loose until a reasonable amount of diesel has flowed through, and then we tighten them. It's working well... and complies with Bosch guidelines

.

Hi Ralf,

I once didn't tighten the retaining nuts sufficiently (due to using makeshift tools).
The engine started, ran "erratically," and showed pulsating fountains from two nozzles, which quickly flooded half of the engine compartment .

Therefore, I've set aside this tactic for now...
The Bosch method, in my opinion, probably only works with two people.
One person plays the organ, and the other shouts "STOP" as soon as juice sprays out of a nozzle, then tightens the nut on it, gives the signal to continue playing, etc.

Or is it feasible for a single person to handle this project on their own?

Well...

'putzlappen rulez'

It's definitely much easier to do it with two people, but if you're alone, a few things are bound to go wrong and potentially cause problems.

They're quite soaked, but otherwise everything is okay...

CU Gremlin.

Hello Ulf,

Congratulations on your article. The compilation of your practical experience is really well done.
However, as the saying goes, where there is much light, there is also shadow. I noticed an error in your article that you might want to correct.

Quote:

... Due to the larger injection nozzle diameter, more fuel flows at full load, and at partial load, a specific amount of diesel can be injected faster, which concentrates the combustion process more in the vicinity of top dead center (TDC) and slightly increases the engine's efficiency.

The statement that concentrating combustion around the top dead center (TDC) improves efficiency is incorrect.
You are probably familiar with the Otto constant-volume cycle and the Diesel constant-pressure cycle. The greater work output of the constant-pressure process is due to the isobaric energy input without pressure surge, which further shifts the adiabatic expansion "to the right" (towards a larger volume). Ideally, a slow fuel injection rate and uniform combustion (=heat addition) are needed to maximize the work output. If you concentrate the fuel injection around Top Dead Center (TDC), you will achieve exactly the opposite: a greater pressure surge (=higher mechanical stress on the engine) and an earlier start of the adiabatic expansion. This will therefore reduce the efficiency!

A faster combustion rate near top dead center (TDC) leads to a process that more closely resembles the ideal thermodynamic cycle of the Otto engine, where energy input is converted into pressure increase.

Take a look at the diagrams for the idealized cycle processes; I'm sure you'll agree with me then.

Regards,
Alex.

What a shoddy job! How could you have possibly missed that?? *shakes head*

donalexo wrote:

The statement that concentrating combustion around the top dead center (TDC) improves efficiency is incorrect.

Hi Donalexo.

I'm not trying to contradict you, but the logic tells me that it actually improves efficiency. For example, if you compare a 90hp AGR engine that has been chipped to 130 hp with an 110hp AFN engine that has been moderately boosted to 135 hp through chipping, you will notice significant soot formation in the AGR, whereas the AFN shows very little. And this is at the same boost pressure. This is because the injection duration is simply exhausted at that power level, and fuel is still being injected when the piston is already on its way down.
I believe the figures you mentioned refer to average values.
When it comes to tuning, you definitely have to consider other aspects.

You are probably familiar with the Otto cycle and the Diesel cycle.

Both are combined processes, but the diesel process leans more towards being a constant-pressure process. However, it is undeniable that the constant-volume process has a higher efficiency.

And if, for reasons of strength, the maximum pressure that can be achieved is limited, then the efficiency is best when a constant volume combustion occurs up to that peak pressure, and then (necessarily) continues with constant pressure.

Best regards, Ernst.

Hello everyone.

I haven't studied anything related to mechanical engineering – my description of the lower combustion concentration in the top dead center (TDC) area is based on the consideration that the working pressure has "more time" to perform useful work, i.e., to push the piston down, for a complete and rapid combustion process.
It's different if, for example, only a portion of the fuel is ignited when the piston is already "halfway down."

Okay, please agree on a suitable version – the article may then be corrected accordingly.

Hi,
The countercurrent process has a higher efficiency.
If one desires more power, a real-world engine inevitably exhibits a tendency towards an isochoric process because the peak pressure must be limited.
Furthermore, diesel fuel doesn't ignite quickly enough, and gasoline engines are prone to knocking.

christians wrote:

If one wants more power, a real machine inevitably exhibits a tendency towards an isochoric process because the peak pressure must be limited.

Hi Christian,

Um... as far as I understand it:
Did you not mean "... inevitably a tendency towards an equalization process"?

Hello diesel experts!

I can only say: Ashes to ashes, dust to dust!!!
After reading the response posts here, I've been doing quite a bit of thinking and have dug out my old lecture notes. And lo and behold, I didn't remember some connections correctly anymore.

Here is the corrected version:

The Otto homogeneous charge combustion process consists of two isentropic (non-adiabatic) processes for compression and expansion, and two isothermal state changes that, in the idealized cycle, represent the heat input from combustion (i.e., a sudden combustion with a sharp pressure increase) and the gas exchange at the end of the exhaust stroke.

The diesel constant-pressure process also consists of two isentropic processes (compression and expansion), an isobaric process for the gas exchange, and an isobaric expansion that represents the continuous combustion process without pressure increase (but with simultaneous volume increase).

A significantly better approximation of the actual engine is provided by the so-called Seilinger or mixed comparison process. This consists of an isentropic compression, an isothermal heat addition, an isobaric heat addition (expansion), and an isothermal pressure decrease (gas exchange). It represents a combination of constant-pressure and constant-volume processes, and divides the combustion, i.e., the heat addition, into a constant-volume portion and a constant-pressure portion, which provides a significant approximation of the real engine.

The statement by Christians that the isothermal process leads to a higher efficiency is correct if the compression ratio is the same for both processes.
In the case of jet tuning, this prerequisite is met, so that, with respect to the Seilinger process, the uniform combustion ratio increases and the uniform pressure ratio decreases. This indeed leads to a better efficiency ( @Ulf: mea culpa, my statement was incorrect! ).
However, the increased peak pressure during combustion also increases the mechanical stress on the engine.

Now, in my defense: When comparing the thermal efficiency of constant volume and constant pressure processes under the assumption of identical maximum temperatures, the constant pressure process results in the highest efficiency . Unfortunately, I only had the conclusion in mind but forgot the prerequisite of the same maximum temperatures. This condition is naturally not met when tuning a nozzle, as the maximum temperature will increase.

I hope that my clarification has been able to resolve the initial confusion. Oh, and a big compliment to Ulf, who, without any theoretical background, made a perfectly accurate assessment of the situation based purely on his intuition! That speaks volumes about his practical experience!

Ernst's statement is also completely correct. To achieve the maximum thermal efficiency of an engine, one must maximize the constant-volume portion of the combustion process to the point where the mechanical stress limit is reached. Any further increase in efficiency can then only be achieved by increasing the constant-pressure portion.
Here, the mechanical/thermal limits of the materials are the determining factors. Theoretically, one should try to avoid dividing into equal volume and equal pressure portions, but rather cover everything with the equal volume portion. But all theory is gray, and reality imposes other limitations.

Regards,
Alex.

ulf wrote:

christians wrote: If one wants more power, a real machine inevitably exhibits a tendency towards an isochoric process because the peak pressure must be limited. Hi Christian, Um... as far as I understand it: Did you not mean "... inevitably a tendency towards an equalization process"?

Hi,
Sure!
I've edited the post to avoid causing any confusion.

donalexo wrote:

The statement by Christians that the isochoric process leads to a higher efficiency is correct if the compression ratio is the same for both processes. In the case of jet tuning, this prerequisite is met... This indeed leads to a better efficiency

.

Hi Alex,

Okay, then the scholars agree, and the article can (for now) remain as it is.

@Rainer
Following Gremlins' suggestion, I propose adding the following to the end of the article.

Alternative after switching all nozzles at once:
Loosely tighten the injector line banjo bolts on the high-pressure side and briefly engage the starter until diesel fuel clearly leaks out.
Then tighten all the nuts completely and start the engine.
Larger amounts of "pigment" caused by diesel in the engine compartment can be prevented by wiping the injectors with a cloth.

Hello,

A question for those who have already replaced their injectors and driven some kilometers with them:

How has the fuel consumption changed (in city and highway driving)? Do you notice any differences even when driving in the same way?

Best regards, Rainer.

'In December, I swapped out the parts on my 1Z engine. The original parts were reinstalled. Before I changed engines at the end of March, I drove about 8,000 km with this setup. My fuel consumption decreased by approximately 0.3 liters per 100 kilometers. Also, the exhaust smelled like violets again!'