Merkwürdiger Verbrauch | Posts 16+

Hi Eike,

It doesn't sound good...
"But the ALH and my 1Z are fundamentally different concepts. While yours has a VTG turbocharger, I have to deal with the oddity that is the 'wastegate'." "Fortunately, the wastegate doesn't seem to be as prone to failure as the VTG, but that was really the only advantage."
Based on your description and the mention of boost pressure, I would say that something is likely wrong with the system (e.g., the variable turbine geometry, the boost pressure regulator, or there might be leaks).

Hi Ulf & Bertil!

At 2000 rpm, the engine (under full load) operates approximately 10% more efficiently than at 1100 rpm, but its internal frictional losses constantly consume at least 100% more energy per meter traveled.


As you mentioned above, the friction losses are already included in the consumption curve. That's why we achieved 10% greater efficiency DESPITE the higher frictional losses.

However, what you said about downshifting is correct, but it needs to be viewed from a different perspective. Let's refer to the fuel consumption map for the diesel direct injection (DI) system in Figure 5.

Then, we can operate at a constant speed of 2000 RPM while applying a pressure load of 4 bar gauge.
(Moment = Hub Volume * pe / 4π)
According to the diagram, the consumption is 250 g/kWh.

By downshifting, the engine speed is reduced, for example, to 1000 RPM. To maintain the speed, the power must remain constant, which requires increasing the pressure to 8 bar.
Diagram -> 230 g/kWh

Here's how a consumption curve works, simply put. It is also evident that downgrading the gear only results in a decrease in fuel efficiency in very unfavorable situations.

Interestingly, with the highest effective mean pressure in the diagram, a displacement volume of 1.9 liters results in 310 Nm of torque. I bet that diagram represents the AJM.
Regards,
Ernst.http://www.uni-magdeburg.de/MWJ/MWJ2001/tschoeke.pdf{MARKER}

ulf wrote:

... I suspect that the newer TDIs are somewhat restricted in their immediate acceleration so that turbocharger pressure can build up before the fuel pump is fully engaged --> to reduce soot emissions. ...

It's quite possible, but if you've observed something similar, even without a wardrobe, then I'm relieved.

Quote:

... By downshifting, the engine speed is reduced, for example, to 1000 RPM. To maintain the speed, the power must remain constant, and therefore the pressure needs to be increased to 8 bar. Diagram -> 230 g/kWh ...

Good explanation. I wasn't aware of that until now. Thank you, Ernst!

Are you referring to downshifting to the next higher gear, or (upshifting)? Otherwise, the RPM wouldn't decrease, but would increase... It all depends on how you define it...

Ernst S. wrote:

Then, we can operate at a constant speed of 2000 RPM while applying a pressure load of 4 bar gauge. (Moment = Hub Volume * pe / 4π) According to the diagram, the consumption is 250 g/kWh. By downshifting, the engine speed is reduced, for example, to 1000 RPM. To maintain the speed, the power must remain constant, which requires increasing the pressure to 8 bar. Diagram -> 230 g/kWh Here's how a consumption curve works. . .

Hi Ernst,

I probably should have described it in convoluted prose, like so...

"at low load (3. "When driving at a slow speed with little acceleration, frictional losses become proportionally more significant than in 5th gear. However, with a bit more acceleration, it's better to shift up and drive at the lowest possible RPM, as long as you're not straining the engine."

. . . but of course, I'm happy that my approach is even "scientifically sound" .

Are you referring to downshifting as shifting to the next higher gear, or (upshifting)? Otherwise, the RPM wouldn't decrease but would increase... It's all a matter of definition...

Oops. My mistake... I meant 'upshift'.

However, I also don't think it's good to drive at engine speeds much below 2000 RPM. Not only is it not fun to drive, but the exhaust emissions are also very poor below 1600 RPM and under high load. (Unfortunately, I can't provide any emission maps; I only have some in my notes.)

I'd rather use 5% more fuel if it means my engine doesn't produce excessive soot.
Best regards, Ernst.

Hi Ulf,

Then we were talking past each other and meaning the same thing.

Everything is clear!

@eike


http://www.ralfhandel.de/ladedruck.jpg

@ernst

310Nm...but the question is WHERE? If you take the mean pressure as a basis, you only get the generated torque, not the torque available at the clutch...but 100Nm shouldn't remain in the engine and auxiliary components http://www.ralfhandel.de/ladedruck2.jpg.

Sure, here's the translation:

'CU Ralf' translates to 'See you, Ralf' or 'Talk to you later, Ralf.' It's a casual way of saying goodbye.

310Nm... but the question is WHERE? If you take the mean pressure as a basis, you only get the generated torque, not the torque available at the clutch. However, 100Nm shouldn't remain within the engine and auxiliary components.


What kind of 100Nm?

Here's the calculation again: Based on the diagram, I'm taking 21 bar of effective average pressure. 'And because, with a displacement volume of 1.9 liters, the torque would be calculated as M = pe * Vh / 4Pi = 2100000 * 0.0019 / 12.57 = 317 Nm, I guessed that this characteristic curve corresponded to the AJM engine (around 310 Nm)... it could also be another engine... it's not that important to me.'

If the diagram were labeled 'induced mean pressure,' the friction, which contributes approximately 1-2 bar of 'friction mean pressure,' would still be included. However, the moment resulting from the 'effective mean pressure' is freely available at the crankshaft.
Best regards, Ernst.

Hello Ernst,

I also don't think it's good to drive much below 2000 RPM. Not only is it not fun to drive, but the exhaust emissions are also very poor below 1600 RPM and under high load. (Unfortunately, I can't provide any emission maps; I only have some in my notes.)


I'm interested in what you said about soot. Intuitively, I would have assumed that less soot is produced at low speeds, because there is more time available for combustion. The injection duration should be approximately constant for the same amount of fuel (unless dynamic effects in the electronic fuel injection system and the 'antler' design change significantly with speed), and therefore, at low speeds, it should occupy a smaller crank angle.
Of course, this consideration only applies under otherwise unchanged conditions, such as the air mass in the cylinder and the absolute amount of fuel injected.

Okay, hopefully I didn't completely mess that up...

'By the way, I drive an AFN in an A4 and I usually shift to the next higher gear around 2000 rpm, so the engine speed stays around 1500 rpm, and I often wish I had a 6th gear.' Gang

Regards,
Udo.

Udo wrote:

The injection duration should ideally remain relatively constant for the same amount of fuel injected (except for dynamic effects in the ESP and 'horn' which change significantly with engine speed), and therefore require a smaller crankshaft angle at lower engine speeds.

Hi Udo,

I think you might have misunderstood something.
The same amount of fuel is always injected over the same crank angle, because the fuel pump's delivery rate is determined by the engine speed.
Therefore, for example, at 1500 rpm, it takes twice as long (in terms of time) to inject the same amount of substance X compared to 3000 rpm.

So, it means that the highest injection pressure is reached at the highest engine speed, or that when driving slowly in the highest gear, the atomization is worse, and therefore the exhaust emissions can be really bad.

Hi.

ulf wrote:

The same amount of fuel is always injected over the same crank angle, because the fuel pump's delivery rate is determined by the engine speed. Therefore, for example, at 1500 rpm, it takes twice as long (in terms of time) to inject the same amount of substance X compared to 3000 rpm. So, it means that the highest injection pressure is reached in the highest speed range, or that when cruising in the highest gear, the atomization is worse, and therefore the exhaust gases can really be bad.

Are you sure? To my knowledge, it's actually the opposite. I think there's ALWAYS the same injection pressure, and ALWAYS the same amount is injected per unit of time. That's why it's possible to achieve almost the same power at 2,000 RPM as at 4,000 RPM, which is especially evident in vehicles with chip tuning, where the torque limit at low RPM represents the material's load capacity. It's always possible to inject the same amount of substance each time, as long as the injection duration remains the same, right?

Best regards,
Uwe

Uwe wrote:

I think that there is ALWAYS the same injection pressure, and that ALWAYS the same amount is injected per unit of time. Therefore, it is possible to achieve almost the same power output at 2,000 revolutions per minute as at 4,000 revolutions per minute . . .

Hi Uwe,

What you are describing is more likely the Common Rail principle.
Although the pressure varies depending on the load and speed, this is done to achieve the optimal injection duration (as a time) in each case.

The VPs basically work the way I described.

Hmmm......





Best regards,
Uwe

Are you sure? To my knowledge, it's actually the opposite. I think there is ALWAYS the same injection pressure, and ALWAYS the same amount is injected per unit of time. That's why, for example, almost the same power can be achieved at 2,000 RPM as at 4,000 RPM, which is particularly evident in chip-tuned engines, where the torque limit at low RPM represents the material's load capacity. It's always possible to inject the same amount of substance each time, as long as the injection duration remains the same, right?
Best regards, Uwe

Okay... third and last attempt (damn thunderstorms ).


In VE (variable Einspritzung) and PD (direkteinspritzung) systems, pump elements are used. Specifically, a plunger pumps the fuel. The stroke of the plunger, which represents the maximum pump volume, is always the same. This is simply how it works when camshafts or rocker arms actuate the plunger.

The amount of fuel injected depends *only* on the injection duration. This duration, in turn, is limited. The start of injection cannot be arbitrarily set, for reasons related to both the mechanics and the ignition delay of the fuel. Therefore, with variable valve timing (VVT) and direct injection (DI), only extending the injection duration is possible. However, this extension cannot be unlimited. On the one hand, the piston stroke eventually ends. On the other hand, otherwise the pistons would melt, or the injection would continue even after the piston has already moved back towards the top dead center (TDC) position.
The injection pressure depends only on the speed of the pump plunger. The parameters of volume and nozzle opening remain constant. The speed of the camshaft is dependent on the engine speed. (For comparison: nozzle opening pressure is 190 bar, while the injection pressure is 1800 bar in the VP37, and 2200 bar in the PD).

Here lies the disadvantage of these systems: in the partial load range and at low speeds, the injection pressure is very low.

In gasoline direct injection (GDI) systems (and this includes gasoline injection!), the amount of fuel injected depends only on the nozzle opening, the pressure difference between the fuel rail and the combustion chamber (or intake manifold), and the duration the nozzle is open. While gasoline is injected at a constant pressure difference, the fuel rail pressure is controlled in diesel systems. Even at partial load, diesel systems don't operate at full fuel rail pressure, because while it would save fuel, it would also cause excessive engine knocking.
'Even CR systems cannot inject arbitrary amounts of fuel. The start of injection and the duration of injection are also fixed. Given a maximum pressure, only a specific amount of fuel can be delivered through the injectors.'

Larger nozzle openings deliver maximum amounts of fuel, but in the partial load range, they lead to disadvantages such as increased fuel consumption and black smoke (because the spray pattern becomes significantly worse). CR has an advantage here because the rail pressure can be controlled within a wide range. However, even here, the high-pressure pump is driven by the engine, so it may not necessarily be able to deliver full pressure at low engine speeds.

CU Gremlin.

@ Gremlin!

Could it be that more fuel is injected when using fuel with a higher viscosity (thicker, lower temperature)? If so, why?

Best regards,
Uwe

Hello!

I was just about to write something about fuel injection pressure, but I wouldn't have come close to explaining it as well as .

The following is responsible for soot formation at full load and engine speeds below approximately 1500 RPM:

Because no emissions test checks this specific area of the engine's performance characteristics, the developer can allow for a higher soot value in order to increase torque.
However, it's only intended as a safety reserve and shouldn't be used to shift into the 5th gear when driving uphill at 50 km/h.
And that's why engine speeds below 1600 RPM are definitely suitable for cruising, but not for accelerating or driving uphill with full power.
Best regards,
Ernst.