It really sounds to like to me you don't have any sort of grasp why the EGR or DPF is in place or what they do.
The EGR is in place to reduce NOx emissions. If your EGR was wide open (100%) you'd be killing combustion in your engine and GREATLY reducing NOx emissions. NOx is formed when the combustion temperatures get too high. I believe the number is in excess of 1700°F. One of the ways to combat this is by introducing exhaust gasses back into the combustion chamber. This site tells it like it is:
Exhaust gas recirculation (EGR) is an effective means of controlling the emission of oxides of nitrogen (NOx). The role of EGR in the combustion event is to act as an inert diluent to the combustion air, reducing the oxygen concentration and resulting flame temperatures.
The Diesel Particulate Filter (DPF) doesn't do anything with NOx. The DPF lets whatever NOx is present in the exhaust pass right through, then (in modern vehicles ... well, I guess if it has a DPF, it's fairly modern anyway) it gets hit with Diesel Exhaust Fluid (DEF), which heats up in the exhaust, breaks apart into NH3 and CO2, where the NH3 reacts with the NOx to create Nitrogen and H20.
To this mind if this map is modified to constant value 100% (the valve is always open), I am interested in the consequences. Indeed, if the valve is always open, the engine temperature should be higher.
No. If you had the EGR always open, you'd be dumping tons (not literally) of exhaust into your combustion chamber and pretty much killing the combustion process. If it ran, it would run very poorly and temps would go down, not up.
Also if it's open, how does the engine will understand he needs more pure air from the exterior (is it just done by pressure balance?)
The whole idea of an EGR is to allow less "pure air from the exterior" into the combustion chamber. As stated above, this is what controls the combustion process and allows it to run a little bit cooler, thus creating less NOx during the combustion process.
What about the DPF : if the EGR valve is always open, more (nox) particules will reach the DPF then could the DPF be compromised in the short term use ?
I think I explained why this is wrong above, but realize, NOx is a gas not a solid (or particle) and the DPF doesn't do anything with it. If the EGR valve is always open, you won't be creating much NOx anyways, that is if you can get the engine to run in the first place.
