Duramax vs Cummins Emission Approach

[TDIwyse]

Since Cummins was able to meet NOx emission regulations without an EGR system, it got me curious as the pros and cons of the different approaches. I was especially interested since the guys with the new engines (the 600’s) have been reporting poor economy numbers as compared to the previous HO engines, while the Duramax folks don’t seem to be getting any worse mileage.

I emailed Cummins and asked about economy impact due to their emission approach and got a non-answer answer (they didn’t address the specifics of the question). So searching the net I came across this study located at: http://www.epa.gov/otaq/regs/hd-hwy/1997frm/r97009.pdf

It is very interesting reading on the different approaches to emission compliance. It looks like the Cummins is using the Lean NOx Catalyst approach versus the cooled EGR approach of the Duramax. On page 5-22 the conclusion is this approach will cost approximately ~4-5% mileage impact due to the late injection event (the third injection event Cummins mentions in the 600 promotional stuff?).

The cooled EGR method shows a mileage impact much lower. It’s showed to be in the ~1-2% range on page 5-13. Negatives for the EGR, however, include oil contaminant issues. Approaches to eliminate/reduce this problem are discussed as well.

[OC_DMAX]

I ran across a very similar (maybe the same) type of document on the CARB site (California Air Resources Board) maybe over a year ago. It was interesting reading.

There were (are) two emission break-points (as far as I could determine). One in 2004 and the other in 2007. There will be a minor blip in 2006 when reformulated diesel fuel hits the market.

My take (and this is strickly a guess) is that the GM engineers were designing for the 2007 goal when they re-designed the LB7 into the LLY. So they included the EGR and CAT. The 2007 version of the LLY will most likely include some form of exhaust after treatment, but will not be a complete engine redesign. I am guessing that the Cummins engineers took an interim approach and built something that works for 2004 through 2006. But in 2007, they will add the EGR and some form of exhaust after-treatment. The above is only my opinion but is based on reading numerous CARB and EPA documents on what will be required to meet the 2007 standards.

[ 02-26-2004, 12:02 PM: Message edited by: OC_DMAX ]