Quote:
Originally Posted by pgfpro
For Cold EGR on my engine there are a few advantages I have found.
1) Knock Reduction.
I have found that when Cold EGR is enable I can maintain high load and decrease the air to fuel ratio (add fuel) and lower BSFC from increasing the timing advance while maintaining high load. A traditional HOT EGR would increase a tendency to knock and timing advance would have to be decreased.
OK now this is where it gets confusing. With my ability to run Ultra Lean Burn I have to increase timing advance a ton to make any power due to lean burn's slow burn rate. This helps a ton with pumping losses (running at 0 inch/hg to 2 psi). But there's a point of diminishing returns. Running this lean reduces pumping losses a ton, but at the same time increases BSFC due to a poorer efficiency due to running a higher timing advance. So by running mass amounts of cold EGR to keep from knocking I can now increase the fuel amounts for a more efficient BSFC with out losing high load due to less mass air. Where before if I were to add fuel the engine would increase its power due to the large amounts of air from the lean condition. This would in turn make me have to back off the throttle in which would increase pumping losses.
|
According to this article, it's not the timing advance that hurt per say, but the very low load.
http://www.swri.org/3pubs/ttoday/Sum...n-and-Cool.pdf
At low loads, you're essentially losing a bunch of heat, and that's what hurts efficiency. When you add cooled EGR, you reduce the peak combustion temperatures, which reduces the amount of heat you're loosing to the block/coolant. You should also be able to increase the amount of advance on cooled EGR to help a little bit with efficiency. Another benefit of cooled EGR, and turbocharging in general, is recycling heat, which helps with efficiency in general.