I can explain that...
IF you design the exhaust manifold in such a way that you have a relatively high pressure there to aid high pressure EGR feedback, there's a BSFC to be had with the EGR valve open VS closed. This is how most HP EGR systems are setup as it's easy and cheap to do.
However, if you have a low pressure in the exhaust manifold there's a definite BSFC to be had at all times, but EGR is trickier to implement. You'll likely need to close a throttle valve partially to induce a lower pressure in the intake manifold and suck in exhaust gas.
I removed the EGR and the restriction in the exhaust on a previous car (very tight radius and very small diameter bend just after the turbo) and gained a LOT efficiency. not much to be gained or maybe nothing without redesigning the exhaust.
Newer engines use the DPF to create a higher pressure upstream.
IF you design the exhaust manifold in such a way that you have a relatively high pressure there to aid high pressure EGR feedback, there's a BSFC to be had with the EGR valve open VS closed. This is how most HP EGR systems are setup as it's easy and cheap to do.
However, if you have a low pressure in the exhaust manifold there's a definite BSFC to be had at all times, but EGR is trickier to implement. You'll likely need to close a throttle valve partially to induce a lower pressure in the intake manifold and suck in exhaust gas.
I removed the EGR and the restriction in the exhaust on a previous car (very tight radius and very small diameter bend just after the turbo) and gained a LOT efficiency. not much to be gained or maybe nothing without redesigning the exhaust.
Newer engines use the DPF to create a higher pressure upstream.