My replies are not intended to contradict anything that has been put forward, but merely to add some clarity or perhaps look at things from a different angle.
As always my input is open to correction & if anyone sees anything that is blatantly wrong or even debateable, then I am happy to be corrected or have my opinions realigned . My apologies if anyone feels that I was nitpicking.
Internal EGR is an interesting subject Mark. As well as the more commonly known reasons, manufacturers are using variable valve timing systems (possibly more so on petrol variants) to adjust valve overlap for internal EGR regulation I believe. This is yet another technology that lurks behind the scenes which many would not be aware of.
Like all things automotive, the subjects can become very deep. I am sorry if I have diverted the thread too far off track.
Cheers all
Dave