Quote:
Originally Posted by seattle smitty
Well, this answer surprises me, Steve. It would seem that EGR requires you to light the fire earlier precisely because, as you say, " . . . the recirculated exhaust gas does not burn very well." If I understand you, it seems to contradict what I have read in other places, if I understood them.
Here's a quote from, "Fuel Economy in Road Vehicles Powered by Spark Ignition Engines," J. Hilliard & G. Springer, 1984:
" . . . the addition of EGR will cause an increase in fuel consumption at constant spark advance. This is because EGR tends to slow the burning rate in the cylinder thereby introducing an effective spark retard. If, however, the spark advance is increased as EGR is added in a consistent manner, the NOx will reduce as before, but fuel consumption will remain nearly constant."
What am I not getting here?
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Ok some confusion here - I need to take more time to compose what I am trying to put over.
Here is what I originally wrote:
Although you might initially think that the cooler combution chamber temperatures caused by an EGR system would allow you to run more timing, this is not so. The reason being, that the recirculated exhaust gas does not burn very well.
Here is how it should have come out.
It is not so much the charge temerature that is the issue with regards to timing on an EGR engine. The reason the engine needs more timing is principly due to the exhaust gas not burning very well (actually it does not really burn at all since it is already burned.) It is the EGR's effect that we have to counter as it has more influence on the speed of combustion than the temperature unless things are borderline detonation from the temperature involved. EGR needs more advance - disconnect it and the stock distributor will, as you found, more than likley, have too much advance. Diconnect the vavuum advance altogether and the mileage will drop - usually by quite a margin.
Hope that clears things up,
Steve