NefMoto

I was reading over some pros/cons of anti-lag articles and one concluded that "Starting in 2002 new anti-lag techniques, such as Exhaust Gas Recirculation (EGR), are slowly overtaking the method described above as they are kinder on the engine's mechanical parts."  What on earth is this man talking about and is it something we can figure out?

Hey I was actually looking at VVT (Variable Vane Turbo) setups to see how they would work and I noticed that they don't usually use a wastegate. However they do use EGR! I remember reading somewhere that the 997 Turbo was the first (or one of the few) engines to use Variable Vane Turbos due to previous problems with overly high exhaust temps. I guess diesel temps are lower  :-\

Either way, I saw a diagram that showed two different types of EGR: High and Low pressure. High pressure is tapped from the exhaust manifold or in VVTurbo situations from the exducer of the turbo. On low pressure systems I think it is from somewhere behind the cats. From there, it goes to the intake manifold and is incorporated into the mixture through the use of a valve. Ideally the valve should be close in wide open situations because you don't want too much exhaust interfering with combustion.

I know that EGR is mainly used to reduce NOx emissions, and in diesel (and the 997) cars to help with the Variable Vane setups. I can't really see how this would effect anti-lag without a VVT. However, figuring out how to tune for those turbos and EGR would be awesome!

Here are some references:
http://www.ni.com/white-paper/13516/en
http://paultan.org/2006/08/16/how-does-variable-turbine-geometry-work/

Rally EGR is different from the EGR used for emissions purposes.  It isn't suitable for a road car and the turbos wouldn't last 5 minutes.

Rick

Hi,
The EGR in series production engines is done to reduce the amount of Oxigen in the cylinder. There are mainly 3 mechanisms to bulit NOX, but the most important one is the thermal NO. This NO is built in the high temperature zones of the flame (1xO2 is split into 2xO and this reacts with the N of the N2 of the air -> Zeldovich). So if there is no O2 then there is no NO(x). This works fine as long as you have lambda (=1) controled systems. In Diesel Engines or DI gasoline Engines this does not work any more because you have lambda higher than 1 (for FC reduction). With this system it is by the way clear, that here is a direct relation between Lambda and power (lambda changes ->quality controlled), different to the Lambda 1 controlled engines where the quantity of the homogenious mixture defines the load (quantity controilled).
To reduce the amount of O2 , part of the EG is put back into the cylinder, and therefore filled up with (mainly) N2 and CO2 . 

There are two ways to get the Exhaust gas back into the cylinder:
internal  EGR:
This EGR is realized with valve timing, there are several different concepts (cycles). One of them is also used in newer Audi Gasoline (DI) engines. There the EG is pushed back into the intake  and then in the next cycle sucked into the Cylinder. For this reason the intake valves look like Sh** even after 20000km of driving.
external EGR:
here the exhaust gas is taken upstrem the turbine and via a valve brought back (through a cooler an then) into the intake manifold. This is the so called high pressure EGR system (pressure upstream turbine is high). The low pressure EGR system is (as far as I know) only used in Diesel engines. Here the exhaust gas is taken downstream the particulate filter and the brought back into the compressor inlet (not intake manifold). The benefit is, that the impact on the boost control is reduced, because the pressure upstream turbine is still high. In addition the exhaust gas is Particle free because it is taken downstream DPF. Of course the (not damaged) DPF is a must... otherwise: compressor dead. ;D ;D
 One basic reason of course is also the lower temperature of the exhaust gas when taken downstream DPF-> no add. cooler required.

Regarding the VVT turbocharger: the maximum turbo temperature of typical Diesel applications is max. 850°C. Peaks can be higher up to 900deg, but the lifetime of the TC is then reduced significantly. For Diesel engines this works fine, because for the Diesel you have naturally (as explained above) the boost independent from the load. By the way with the vanes also the exhaust backpressure can be influenced independently from the engine load, so an exhaust gas pressure can be created which is high enough to have a pressure drop between upstream turbine an intake manifold (to make high pressure EGR).

I hope to have explained it in an understandable way  :) :)

i think the OLD lancers evo's had EGR antilag built into the japanese ones

oops... and there is a ton of info online about that system and how it works, and tons of info on how to make your own :)

Well I'll be damned, didn't expect such an out pouring of great information on this subject! Love this forum.