AFN+6 Gang+Motorkennfeld | Posts 32+

ddrler wrote:

No, I mean the minimum injection amount.

Presumably, the injection amount cannot be adjusted continuously from 0 mg in steps.

ddrler wrote:

At least, the amount of idle speed (or even below that) can be adjusted upwards. This is always exceeded in the partial load range being discussed here, so there is no problem with the amount.

Reduce the quantity and set the start time earlier; performance should remain the same.

ddrler wrote:

As far as it's correct: When adjusted towards an earlier timing (compared to the standard setting), the same power output can be achieved with a smaller amount of fuel in the partial load range, compared to the standard setting.

The dp/dalpha value should be lower, and therefore it shouldn't produce as much "Genagel". In my opinion, the noise level is the same.}
"Haha... And that's where the problem lies. When injected into the OT (Over Timing), the peak pressure is lower. While the efficiency is reduced (which means higher fuel consumption), the peak pressure is lower, which in turn reduces noise and stress on the head gasket (although the latter is not a concern under partial load conditions)."

Regards,
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It can also be used as a verb, meaning "to gust."

guste100 wrote:

"Haha... And that's where the problem lies. When injected into the OT (Over Timing), the peak pressure is lower. While the efficiency is reduced (which means higher fuel consumption), the peak pressure is lower, which in turn reduces noise and stress on the head gasket (although the latter is not a concern under partial load conditions)."

I'm not entirely sure right now, but I wouldn't attribute the noise to the peak pressure. In my opinion, the rate of pressure increase is much more significant. I don't have a better source available at the moment.

http://de.wikipedia.org/wiki/Direkteinspritzung#Druckanstieg.2C_Ger.C3.A4usch

Hello,

ddrler wrote:

I'm not entirely sure right now, but I wouldn't attribute the noise to the peak pressure.

In my opinion, the pressure rise gradient is much more significant.

Sure. But it's also larger if the injection happens earlier. Or conversely, if the pressure wave has to chase after the piston, the pressure increases more slowly and reaches a lower peak value.
The noise comes from misfire, as stated in your Wikipedia link: nothing burns initially, then everything ignites at once -> a steep pressure increase -> noise. In partial load conditions, the misfire is longer than under full load, which explains the "bathtub" shape of the spark advance curve. If more fuel is injected, the combustion chamber temperature increases, and the fuel ignites faster and more evenly, so it can be injected earlier. Turbocharger boost pressure also has an influence (more oxygen molecules per volume are available near the droplets). In our old swirl chamber engines, you can clearly hear when the turbo kicks in: from the moment it starts boosting, there's a sudden silence. With the AFN engine and its advance timing, I hear this with diesel too (as soon as you give it gas, it becomes quiet), but with gasoline, it always runs quietly.
Short summary: Guste is of course right; Diesel engines make a significant amount of noise at low RPMs, especially when you're limiting the SB map (keyword: truck, tractor, etc.). It injects fuel earlier, which reduces the amount but makes it louder. My girlfriend can actually tell what's in the tank by the engine sound: "Are you out of oil? That thing is making noise and not pulling." }


Best regards, Uli.

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If you're talking about multiple injections: A particular type of VP system might not be able to handle that...

At least not the edge-based systems .

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So: Then please explain how you plan to improve comfort and reduce noise in the partial load range without delaying the injection timing.

"Even with TDIs operating close to the smoking limit, the extremely high ARF (Air Reservoir Flow) rates result in relatively soft performance... of course, this doesn't offer any fuel efficiency benefits. Moreover, the ARF effect can still be observed in newer engines."

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Reduce the amount and set it earlier; performance should remain the same. The derivative with respect to alpha (dp/dalpha) should be lower, which would also result in less "Genagel". In my opinion, the noise level should be the same.

That's why Common Rail systems exist. A small amount of fuel (sometimes two amounts with piezo injectors) is injected approximately 35-10 degrees before top dead center (TDC). This increases the temperature and compression end pressure, allowing the main injection (which is injected relatively late) to ignite immediately, preventing any accumulation of fuel that could then burn explosively (and loudly).

The pre-injection sequences of various VP37 and "older" common rail systems are "coupled" pre-injections, meaning they are not independent of the main injection event and occur relatively close to it. Newer common rail systems (I'm not sure how widely they are in production yet) may also have decoupled pre-injection sequences.

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These engines make quite a racket at low RPMs when you limit the speed limiter setting like I do (keyword: truck, tractor, etc.).

The days of trucks and tractors with carburetors are largely over. I have a dataset from a current off-highway engine where the injection timing for the main fuel injection is around 10° before top dead center (BTDC) across a wide range of partial loads.
Since there have been emission regulations in place, fuel efficiency is no longer the primary focus; instead, any improvements in fuel efficiency are achieved only through intelligent, fully variable transmissions, and even then, only by lowering the engine speed, which brings us back to the beginning of this discussion.