DPF / EGR thoughts (non Dodge specific)

[Shelby Griggs]

A couple of thoughts on DPF's and EGR for discussion on a Sunday afternoon.



There seems to be quite a few teething problems with DPF's in the Dodge trucks, how about on other equipment with larger displacement, say on highway trucks? I was just wondering if "soot" issues are related to light(er) duty applications or if this problem is plaguing other sizes and makes of diesels too?



If the DPF is doing its job, why couldn't treated exhaust be routed back into the intake for the EGR? That would be more complex plumbing wise, BUT you wouldn't be dumping soot back into the motor, it seems there would be less to go wrong in a cleaner environment? I am sure somebody must of thought of that AND it must not work?



SHG

 

[TAbbott]

That was Cat's last great idea before exiting the over the road engine market. They've had that system in place for a year or so by now. Probably is a better idea, but wasn't good enough to make them competitive or even meet 2010 emission standards.

 

[Cattletrkr]

Ya wouldn't think it would be too hard to cool it either since it has such a long ways to go to get back.

 

[jwgary]

There might be a pressure issue that once you get past the DPF there isn't enough pressure to overcome the boost in the intake.

 

[snoman102]

The re-circulated gas would be cleaner if it was taken from post doc/dpf, but then your doc/dpf would be receiving even more crap to filter. Know what I mean?

 

[abrankod]

I just got done spec'ing DPF retrofits on a set of sightseeing buses in NYC, and have been in contact with both Cummins and Johnson Matthey (the producers of the dpfs that Cummins markets under the Fleetguard name,) and I've basically come to the conclusion that dodge, and ford are basically screwing their customers with the type of DPF that they use in their vehicles. The system in place on the 6. 7l engine is basically a low cost, first generation system that needs frequent regenerations if any significant idle time is accumulated. Furthermore, the inability to FORCE a regeneration in-vehicle is utterly idiotic, since the system for sensing backpressure/temp can and does malfunction often causing excess fuel useage and poor performance.



The buses that we were working with are running 300HP California spec HPCR 5. 9l engines with EGR. Both Cummins and Johnson Matthey both recommended their CCRT unit for the application due to the new technology working at full power with EGTs as low as 200°C for extended periods of time. Sooting of the DPF is virtually eliminated. This benefits the buses since they operate at low speed/idle conditions for long periods on their slow trips through Manhattan. Another benefit of the system is that it requires NO active regeneration. The system operates happily till 80-100kmi at which point the DPF is simply opened (the dpf is held together by V-band clamps) and can either be sent back to J-M to be cleaned or cleaned in-house on a machine that basically backflows the system into a filter with a high temperature burner/blower system. The system is both CARB and EPA approved for the upcoming 2010 standards.



The DPF costs $12k for a single unit, but for 50+ units, prices drop below $8k... I'm sure if this system was implemented by Dodge or another OEM, prices would drop far further as well.



You can check out the CCRT system at J-M's website (pdf)

or, the whole site.



On to your question about using post-DPF exhaust as the EGR source rather than pre-DPF exhaust. I think the primary reasoning for the use of pre-DPF exhaust is that a part of the diesel particulate reduction system further oxidizes the particles of soot, therefore less oxygen would be available for the recirculation pathway. Part of the reason that only diesels even HAVE EGR coolers, is that since they are lean-burn engines, the exhaust still contains a useable charge of oxygen which, when cooled, supplements the burn along with re-burning some of the unburnt particles etc.



If you have any questions, don't hesitate to ask.



-Dan

 

[jwgary]

If you go to the J-M website in the post above you will see an example of just what Shelby is asking about. They call it EGRT and it's just below the aforementioned CCRT in the list. It looks like they get better performance out of that than with SCR which practically everyone swears is the only way to meet 2010 or 2014 emissions.

 

[Shelby Griggs]

If that EGRT works that would seem to be MUCH better than the current fuel dosing AND all that soot going back into the engine to clog things up. One has to wonder how long Cummins will continue down the current road before trying a different technology??? I am approaching replacement of my 2001, BUT can hold out for a while yet! If I had faith that the 2008's or 2009's were going too be trouble free, I would probably order one this fall, but I think I will take a wait and see attitude for a bit longer. I hope they get this figured out pretty soon.



SHG

 

[ENafziger]

One of the biggest limitations to recirculating exhaust post-DPF is there is not enough pressure to drive the loop. We are working on some smaller diesel engines right now that utilize both high and low pressure egr loops, with cooling on both... we have a patent in right now on how to drive the pressure of the low side, but I can't talk about it quite yet. It won't be long until you'll be seeing 2 egr loops though, and probably 2 or 3 separate propylene glycol cooling systems!

--Eric

 

[snoman102]

If you go to the J-M website in the post above you will see an example of just what Shelby is asking about. They call it EGRT and it's just below the aforementioned CCRT in the list. It looks like they get better performance out of that than with SCR which practically everyone swears is the only way to meet 2010 or 2014 emissions.

I can tell you that cummins will not be using urea on any of there heavy duty engine in 2010, but will be on the midrange engines.



Good info abrankod.