I've been mulling this around for a while now and its definitely an area to look into. How can we use EGR to increase our FE?
EGR could allows us to decrease pumping losses for the same power output, somewhat similar to lean burn. However, it doesn't have the NOx problem that lean burn does since there is not an overabundance of oxygen in the air/fuel mixture.
Lets take a look at how the OEMs utilize EGR. From
this Toyota article, it seems they are using it solely as a means to decrease NOx emissions. I think this can be backed up by noting that the 96 Paseo had EGR vs the 97 which did not, and the 97 has a higher EPA mpg rating. So, we need to figure out how to alter EGR for our uses.
Quoting the article:
Quote:
High EGR Flow is necessary during cruising and mid range acceleration, when combustion temperatures are typically very high.
Low EGR flow is needed during low speed and light load conditions.
No EGR flow should occur during conditions when EGR operation could adversely affect engine operating efficiency or vehicle driveability (engine warm up, idle, wide open throttle, etc.)
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Why would we not want high EGR flow at idle and light loads? Pumping losses are the greatest when the throttle is closed or close to it. Low speed city driving mileage would be noticeably improved.
I also think real gains could be had if EGR flow is increased at cruising loads to further decrease pumping losses. This will have a downside, loss of power, but I think many here are willing to give some up. Also, if we again make it similar to learn burn, we could simply make some override switch that pops us out of 'EGR mode' and back to normal mode for power.
Now, I don't think any of this would be real easy to implement, but I really think its worth considering. There are definitely problems with EGR. First off it is hot, and its also messy (carbon build up). There are additional things such as ignition timing that would need to get looked at to make it a perfect system since an EGR rich mixture will burn slower and require additional ignition advance. There is also a point at which you can no longer dilute the intake charge without causing misfires (same as lean burn), so you can only take EGR so far.
I'm really looking for input, and ideas on how we could use this, the different systems out there, and how control them. I really only know Toyota. Their setup is described in the PDF I linked to. I also know Honda's Insight uses EGR, but it has an electronic actuator that opens and closes the valve. What do other mfgs use?