TDI Engine Speed: Specs and Performance

Hi,
Does anyone know why the latest engines from the group, such as those used in the new A4, can now rev higher than before, with a peak power output at 4400 rpm instead of 4000 rpm, as was the case with the 3.0 V6 TDI?

I've wondered that too.
It's most extreme in the 535D model with its register charging system.
My assumption is that the high charging pressures, which occur at high speeds, are causing...
that the injected diesel fuel still ignites reliably (in a timely manner).
As we know, the combustion process in diesel engines lags behind, especially at high engine speeds.
I believe the limiting factor here is the point before OT.
where the temperature inside the cylinder has reached the necessary temperature.
to initiate self-ignition.
This is likely to be achieved sooner with the new high-performance engines.
Even with reduced compression, as the "Junge Wilde" (Young Wilds) require .

I'm guessing it's the common rail injection system with high injection pressures. It seems that, even within the increasingly narrow time window at high engine speeds (keyword: ignition delay), higher injection pressures might still allow for a sufficient amount of fuel to be adequately atomized.

I think it's because the pre-injection creates a kind of pre-ignition, which then helps to ignite the main fuel charge.

bastion wrote:

I think it's because there's a kind of pre-ignition caused by the pre-injection, which then helps to ignite / ignite the main amount.

Okay, pre-injection technology has actually been around since the VEP-TDIs.
Common rail systems with piezo injectors offer multiple injections, and these injections can occur independently of the engine's firing sequence, thanks to the constant rail pressure, allowing them to happen quite early before top dead center.

christians wrote:

Does anyone know why the latest engines from the corporation, such as those used in the new A4, can now rev higher than before, with a peak power output of 4400 RPM instead of 4000 RPM in the 3.0 V6 TDI?

[Speculation ON]
As far as I know, the combustion speed of the diesel mixture cannot be increased, so to achieve a useful efficiency at high speeds, one must inject the fuel earlier.
While this increases the peak pressures in the engine's combustion chamber, these can be compensated for in new engine series using appropriately reinforced materials – or perhaps we can simply forgo some of the traditional design margins from the outset...?

After that, the "why" behind the high Pmax speeds seems to me to be simply a matter of a Pmax race: 10% more speed at the same torque results in 10% more Pmax.
[Speculation OFF]

Hm, that's a silly question from me.

I see it the other way around; why do the "older" TDI engines only have a rated RPM of 4000 to 4150 (AFN)?

Die "ganz alten" TD mit Wirbelkammerverfahren (MKB JR oder JX) haben eine Nenndrehzahl von 4500 rpm, sind Wirbelkammerdiesel so viel besser im Verbrennen des Diesels ? Probably not...
Okay, the crankshaft of a JR engine is shorter, which means the inertial forces are lower at high RPM. However, since the bore is only slightly smaller compared to the 1.9 TDI, the same ratios remain.
However, in the 1.9 TD engine (MKB AAZ) with a swirl chamber, Volkswagen also reduced the rated speed to a material-friendly 4000 rpm. Could this be due to the longer stroke?

I won't even talk about those old Mercedes pre-chamber diesel engines; they rev up like gasoline engines to dizzying speeds. Okay, those old Mercedes oil burners also lack torque in the lower RPM range.

Regards,
Jens.

It has been suggested before that, in previous DI engines, the turbocharger was the limiting component, which is why the BMW 535d, with its twin-scroll turbocharger, revs higher. I can only partially understand this, because what would have been wrong with designing a "sports version" of an existing engine? While a larger turbocharger would create a significant turbo lag, it could also provide more power at higher RPMs.

christians wrote:

It was once said that in previous DI engines, the turbocharger was the limiting component, which is why the BMW 535d, with its twin-scroll turbocharger, also revs higher. I can only partially understand this, because what would have prevented designing a "sport version" of an existing engine that, while having a large turbo lag due to a larger turbocharger, would have correspondingly more power at higher RPMs.

Perhaps there is some truth to this, at least in the case of the 2-valve engines, which naturally have a more sluggish gas exchange at higher RPMs.
To achieve proper maximum power (Pmax), one must work with such high pressures and large turbines that the turbo lag becomes quite significant at low RPMs. The corresponding criticisms, for example, of the ARL, point in this direction...

For engines with two valves, this is understandable to some extent, even for common rail (CR) engines, because there would otherwise be a risk of exploding injectors at high speeds. However, if the injectors were also designed for such speeds, the resulting engines would be racing engines rather than sports engines, due to their poor suitability for everyday use. This wouldn't necessarily apply to older CR engines or 24V engines with a VP44 pump.

Hello,

Jens 16syncro wrote:

The "very old" TD engines with swirl chamber technology (MKB JR or JX) have a nominal speed of 4500 rpm. Are swirl chamber diesel engines really that much better at burning diesel? Probably not...

The problem is the cylinder filling at high engine speeds. The WK engines are better in this regard because they have "straight" intake passages. The 1.6 naturally aspirated engines reach their rated speed at 4800 rpm, and the original 1.5 even at 5000 rpm. The VP-TDIs have a swirl channel that restricts the airflow from above. In the 4V engines (if I remember correctly), one channel is swirled to create turbulence at low engine speeds, while the other is straight to ensure proper filling at high speeds.

Quote:

Okay, the hub of a JR engine is shorter, so the inertial forces are lower at high RPM. However, since the bore is only slightly smaller compared to the 1.9 TDI, the same ratios remain. VW also lowered the rated speed to a material-friendly 4000 rpm for the 1.9 TD (MKB AAZ) with swirl chamber, but was this due to the longer stroke?

No. My AAZs all have 4400 as the nominal speed; the idea that the long stroke is the reason for speed limits is more of a pub talk. In the PRG, the guys shift at 6000 rpm.

Best regards, Uli.

Hello!

Here's a little story about it, and it's not a fairy tale!

Many years ago, I worked in a workshop for the German postal service.

There was a Golf 1, with a 1.6-liter engine, which was very noticeable because it was white, unlike the many yellow cars.
It wasn't working quite right; it was always smoking a lot and starting very poorly.
We didn't know what else to do, so we took the fuel injection pump to the Bosch service center. They fixed the pump, but apparently not completely correctly.

After my mandatory military service, the workshop no longer existed, and I had to work as a truck driver.
I've also occasionally driven this car.
Das war voll krass, der hat bis in den Drehzahlhimmel gedreht. Damit war man an jeder Ampel König, der ging im 2. Walk at a pace up to 80.
"And once on the highway, I drove at 170 km/h. It could have even been more, but I stopped there, considering the tires."

I suspect the fuel injection pump wasn't properly regulated. Of course, there was no tachometer in that car, and it also only had a 4-speed transmission.
But those were definitely at or slightly above 6000 RPM.