@Ulf Air intake system

After conducting a few tests, I have come to the following conclusions:

The resonance tube isn't just placed there randomly; it seems to have an influence on the length of the intake path. While more important for naturally aspirated engines than for turbocharged ones, it improves torque at low RPMs.

Your solution to improve the air filter box filling by perforating the air intake snorkel has two sides: it performs poorly at low RPMs, but seems slightly better at high RPMs. I don't fully understand yet why this is so noticeable in naturally aspirated engines (especially at low RPMs). It seems like the two air streams are 'hindering' each other. In other cases, it seems to be better at high RPMs, which would be illogical.

Another idea would be to incorporate a second access point into the box... but I don't have any information about that (maybe I'll try it with a replacement box).

Hi,
The inertia of the air is simply utilized in vacuum cleaners. Longer distances mean a larger volume of air, and therefore more air mass, which flows into the cylinder for a longer duration (in terms of time). This creates a 'recharge' effect until it is slowed down by the piston, which is already on its way back up.

In diesel engines with turbochargers, the mass of air is also utilized to some extent. At lower engine speeds, where the turbocharger is not yet fully engaged, the engine is 'boosted' simply by increasing the mass of air intake. However, this can lead to larger cross-sectional losses at higher engine speeds, which is then partially compensated for by the turbocharger.

I hope you were able to provide a good report.

Best regards.

Hi, I have a problem with my car (60 HP SDI).
A second air intake for the air filter box has been created. The original intake draws air from the right fender. The Polo 6N Sportline has the styling bumper, which, in addition to the fog lights, has a closed air intake. There's a suggested air grille there, but the slats are blocked. I modified it in a way that creates positive pressure inside the air filter housing without affecting the engine's heat dissipation.
It helps with the intake, of course, and there's a noticeable difference, although not a huge one. However, it's very noticeable at temperatures between 4 and 5 degrees Celsius, as it runs best then. This behavior has existed before, but it wasn't as pronounced as it is now.

I'm currently looking for an intercooler (don't laugh).
Because even with a naturally aspirated engine, cold intake air can make a difference.

Best regards,
Ingo

The inertia of the air is simply utilized in vacuum cleaners. Longer distances mean a larger volume of air, and therefore more air mass, which flows into the cylinder for a longer duration (in terms of time). This creates a 'recharge' effect until it is slowed down by the piston, which is already on its way back up.


Well, if you're referring to a certain resonance buildup with that description, it doesn't quite fit. The amount of air drawn in by a naturally aspirated engine is always the same... (depending on displacement and engine speed). When the resonance effect occurs, the intake manifold pressure is slightly greater than 1 bar (1.1-1.2).


In diesel engines with turbochargers, the mass of air is also utilized to some extent. At lower engine speeds, where the turbocharger is not yet fully engaged, the engine is 'boosted' simply by increasing the mass of air intake. However, this can lead to larger cross-sectional losses at higher engine speeds, which is then partially compensated for by the turbocharger.


With Turbo (in general), it's similar... there are systems that combine both principles, etc., so you can't make a blanket statement about it. Charging without turbocharging is highly dependent on the length and cross-section of the intake passages, as well as the valve timing, and therefore also the engine speed.

Hello Uwe,

You were probably faster than me.

But you're right, a liquid-cooled system in a naturally aspirated engine is absolute nonsense.

Hi!

"Please, absolutely do not install an intercooler. In a turbocharged engine, the air gets very hot due to the compression. It then needs to be cooled down. In a naturally aspirated engine, the temperature doesn't change much during intake, or it might even become slightly cooler due to the vacuum created and the associated expansion. With an intercooler, you're just mixing the same temperature air, resulting in zero cooling effect! The intercooler also changes the intake volume, and the charging effect caused by the oscillating air column is lost. Furthermore, the air has to overcome the flow resistance of the intercooler." So, if you use a high-flow nasal cannula (HFNC) and administer oxygen, you might inadvertently cause a "self-inflicted harm" situation, as the patient might end up needing less oxygen later than they would have with conventional oxygen delivery.

Best regards,
Uwe

Docter wrote:

Well, if you mean a certain resonance charging with the description, it doesn't quite work. The amount of air that a naturally aspirated engine draws in is always the same... (depending on displacement and RPM). When the resonance effect occurs, the intake manifold pressure is slightly greater than 1 bar (1.1-1.2)

.

Hi Doc.

Yes, I'm familiar with that effect. For example, I experienced it during compression tests on my last car, a 1.9 Peugeot 205 GTI with clearly visible individual intake runners on the intake manifold. According to the specifications, the compression ratio was around 10, but when I measured it, I got a reading of about 14, if I remember correctly.

I suspect this isn't just a simple resonance effect (which is limited to narrow frequency or RPM ranges), but rather the result of a moving mass of air within a relatively narrow tube, where the velocity increases significantly during intake, increasing nicely with the square of the stored energy (m/2 x v²) and thus providing a significant "boost" even after the piston has already passed top dead center, but the intake valve is still open.
Until the next intake stroke, some of the kinetic energy is converted into compression work in front of the closed valve, so that when the valve opens, the air/fuel mixture is already "under pressure" and rushes into the cylinder.

It's possible that similar effects could occur to a minor extent in TDI engines as well. For me, the 2000-4000 test yielded the same results, whether or not the "trumpet" was present in front of the mass airflow sensor (MAF).

The perforated airbox provided a minimally better boost pressure build-up at low RPM, apparently because the (ridiculously) narrow opening of the intake manifold creates a slight pressure drop, which the turbocharger with the perforated airbox then doesn't have to compensate for.
Due to the louder intake noise, I closed the holes again and instead drilled a few holes in the intake snorkel behind the opening.

But no matter which solution I tried, I never noticed any significant performance differences.

Hi, I once installed a second tube into the air filter on my AJM engine with a chip. The result, when combined with a sports air filter, was a loss of torque across the entire RPM range.

This principle of charging through the inertia of the flowing air column is utilized in tuned intake manifolds. It is based on the principle of the standing wave (a vibrating air column). (Okay, you know what I mean!) An intake manifold can only be optimized for a specific engine speed. The switchable intake manifold uses at least two pipes, allowing the system to be optimized for two different engine speeds.

This achieves the effect that, at specific engine speeds, more air flows into the cylinders than is theoretically possible.

Even as the piston moves upwards again, air is still being 'forced' into the cylinder. More air allows for more fuel to be injected.

Sure, I'm familiar with the issue regarding the swing columns .
I'll just say 'Weckner' (insider joke).

The columns oscillate due to the opening and closing of the intake valves, with pressure drop during valve opening and pressure increase during valve closing. These waves are reflected. Normally, the length is defined from the air intake to the plenum chamber (where is this?). Intake manifold? (in front of the DK?)
That's why I don't quite understand why the resonance tube in the air filter housing still has an effect... And consequently, the influence of so-called... Air Take In: Press the intake air into the air filter box...

Best regards,

Docter wrote:

The columns oscillate due to the opening and closing of the intake valves, with a pressure drop during the intake opening and a pressure increase during the closing. The waves are reflected. Normally, the length is defined from the air intake to the plenum volume (where is that?). Intake manifold? (in front of the DK?) That's why I don't quite understand why the resonance tube in the air filter housing still has an effect... And consequently, the influence of so-called... Air Take In: Press the intake air into the air filter box...

I probably made a small mistake in my thinking. Vibrational phenomena are not limited to a single resonant frequency, but can also cover broader frequency ranges with smaller "amplifications" – something I've known from electronics for quite some time.

The influence of the (measured by total pipe length) ridiculously short trumpet section before the LMM is puzzling to me, especially considering its potential to fundamentally alter the vibrational characteristics.
I suspect the purpose of this part is primarily to reduce turbulence, which leads to flow losses. Similar designs can also be seen on the ports of newer hi-fi bass-reflex speakers. They reduce flow noise, which minimizes turbulence and thus increases the efficiency of the reflector design.

The air intakes are, in my opinion, quite straightforward: they are not intended to alter the resonance characteristics of the intake system, but rather to create a higher absolute pressure level overall (within which the known intake manifold resonances still occur) by simply using the static pressure of the airflow, thereby improving cylinder filling. It's, so to speak, a mini-turbo effect that depends on speed .