Quote:
Originally Posted by mwebb
[COLOR="Lime"]no
actual mass will be Old AF mixture mass less the mass of the Old AF mixture that was displaced by the EGR .
plus the mass of the EGR .
until
the driver steps down on the throttle IF the driver feels the need for more "go"
so essentially
the mass of stuff in the combustion chamber is UN changed by the addition of EGR
until the operator requests more " go " IF the operator request more " go "
so
EGR in and of itself does NOT increase combustion chamber content mass
relative compression and relative engine size are reduced .
all good things . when discussing FE .
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That's all true if you don't mind decelerating where you would have normally held a steady speed, or holding a steady speed where you would have been accelerating before, or accelerating much slower than before.
You could do all of this without the intake charge contamination, by simply using less throttle. The gain in combustion efficiency far outweighs the minuscule increase in throttling suction.
I was talking an apples to apples comparison, which assumes equal engine power output.
Also, as I said, when engine power output doesn't matter so much (you can get away with less), then the EGR isn't such a negative factor.
I believe you about the Metro dropping FE with a malfunctioning EGR system. Did you determine exactly why this happens?
What happens when the EGR is then turned off in the calibration?
Without the added spark advance you could then observe just the effect of the lack of EGR flow. Some algorithms use O2 offsets in the adaptive fueling routine to make up for EGR or AIR-injection. There are also O2 offsets for low RPM operation to make up for small changes in exhaust content due to reversion and charge-bleed during overlap. O2 offsets assume a perfectly functioning completely stock system. Normally you would notice a problem here by watching a WBO2.
Did the system indicate any knock? Did the spark plugs change how they looked?
Without EGR flow, one could assume that peak combustion temp and pressure went up, and some side-effect of this then caused a loss of FE. My initial thought would be too much spark advance under load, even if not enough to cause knock. I've not examined the EGR system on a Metro, so I will hold off on any more speculation there.