I've been reading up a good bit on the new required emissions gear and my head is spinning (it doesn't take much ) and am hoping for some clarification. So if I understand it correctly, there are two factors in cleaner emissions: Particulate matter and nitrogen oxide (Nox). The Diesel Particulate Filter (DPF) handles the particulate matter (soot basically) and the Diesel Oxidation Catalyst (DOC) deals with the Nox...the DOC is closest to the engine followed by the DPF downwind. In order to reach the high temperatures needed to 'clean' the DOC and DPF, the exhaust temps are increased by injecting a small bit of fuel right before the DOC during an active regeneration (not going into the different regen methods).

So...assuming my description above is close to reality, my questions are:
1. Where does the EGR concept fit into the picture and is this being done full-time or only during active regen?
2. If fuel is injected right before the DOC to create the heat, why would EGR be necessary?
3. Are the higher temps (1000+) people are talking about actually going back through the engine? I'm guessing this is during active regen when the fuel is being burned right before the DOC...
4. From what I can tell, the alternate method of using urea to control emissions would replace the need for a DOC but would still require the DPF and EGR correct? (Not used by BLUETECH but interested anyway)

I've done lots of searching and reading but haven't been able to get a complete understanding...thanks in advance for any help with this!

 

EGR is off during regen. This prevents fuel from being diverted into the intake.

This should help explain some things:

http://wiki.dieseltruckresource.com/wiki/6.7_Changes

 

Thanks...That was one of several links I read and after reading over it again some of my questions got answered.

So is the EGR needed more for a way to get the heat up faster for the passive regen (starting at 482 degrees) or is this used in addition to the DOC to reduce NOx? I'm guessing it's a way to reduce NOx. For active regens the EGR is closed off which I think answers one of my questions.

What about question #4...anyone?