I understand that CJ. I have to dispute your figure of 1.9 or 2.4 litres per rev pumping losses though, Because there are only 2 induction cycles for a 4 stroke 4 cylinder engine each revolution, but yes I understand the principle.
Personally I think any reduction in pumping losses (which lets face it is a tiny value considering the engine isn't doing much work thanks to the pressurised charge air) is more than cancelled out by the demand for more power which requires more fuel which inevitably must occur because the reduced combustion temperature (of EGR laden intake gasses) must be coming at a cost to torque output.
Originally Posted by CJ
If you allow some pressurised exhaust back into the inlet, this assists the down strokes, which don't need so much air as you dont need much power.
But the air is also pressurised, you are only adding a slight amount of EGR gas at a slightly higher pressure than the already pressurised intake air (pressurised by the turbo), so I could argue that such a slight reduction in pumping losses comes at a cost to torque being produced as a result of diluting the clean air for combustion with combustion quenching exhaust gasses.
Have you seen any real world data , at least something you can share which shows that EGR gas helps improve economy. I know every manufacturer says that it does so I can't argue against them easily but I do wonder if it is a special case. IE, only in certain driving conditions does the mpg improve.
All the people who fit an EGR blanking plate (Land Rovers, Vectras, Fords) seem to report improved driveability, more power at low revs and better mpg overall..
Even around town I feel I can get at least equal, if not better mpg with a blanked EGR. ....in normal daily driving .
Originally Posted by CJ
but when new, gets you a lower CO2 rating and better MPG
So they say. What matters to me, though, is what happens in practice. If EGR generated mpg gains are only reproduceable wihtin a very band of parameters perhaps they're not so good after all. I haven't read an papers on the subject which look at overall and normal daily driving condition comparisons. All I've seen are papers which show that just for a couple of data points it can be claimed that mpg is improved.....that would be the normal procedure for trying to convince the EURO emmissions board that you were doing something good. In doing so it is easy for them to certificate your design.