Grasping Low Pressure EGR

[GARRIGA]

My thick head might be finally getting it. Confusion was having the LP in addition to the HP and seeing them as two separate parts.

If I’m now grasping this correctly. All exhaust gas first travels through the DPF then through the water cooled LP Cooler then LP pipe then through the HP pipe? No exhaust ever goes through the HP without first being filtered by the DPF which would be maintain by running regenerations along with possibly removing and having cleaned out?

If the above is correct then in theory there should be less soot build up. How I understand it today but might still not be getting it.

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[GARRIGA]

 

[JLURD]

I’m struggling to understand how this improves fuel economy and combustion. I believe in the VW 2.0s they were running a dynamic pre-DPF EGR that would aid in getting the engine up to temperature and then shut off which would yield some mpg benefits with less time spent running an engine below operating temp, but with a cooled system like this, where are fuel economy benefits coming from? I suspect their idea of improved combustion just means they’re more completely burning the fuel by essentially burning some of it twice.

 

[GARRIGA]

I’m not sure how they get 29 from a box on wheels but somehow they did. My fear is soot. Not something I’d be welcoming after 100k miles on a built rig.

 

[JLURD]

I’m not sure how they get 29 from a box on wheels but somehow they did. My fear is soot. Not something I’d be welcoming after 100k miles on a built rig.

I’ve been meaning to pull my diffuser tube to give folks an idea of soot buildup over limited mileage. We’ll see what kind of time I have tomorrow.

 

[GARRIGA]

Ca

I’ve been meaning to pull my diffuser tube to give folks an idea of soot buildup over limited mileage. We’ll see what kind of time I have tomorrow.

Cab you confirm that flow into the HP is only from the LP?

 

[JLURD]

Ca

Cab you confirm that flow into the HP is only from the LP?

I hav no clue how one could prove that outside of asking an engineer who designed the system.

 

[BuffaloBill]

Ca

Cab you confirm that flow into the HP is only from the LP?

If one of us were willing to disassemble our new diesel, I bet we could figure that out by seeing where the egr valves and passages run. Not sure I want to do that just yet.....

 

[GARRIGA]

Found this article. Perhaps there’s a separate HP and LP based on engine temperatures. This is so confusing. LoL

When I was young I knew everything about what my engine was doing and what was needed to get more HP. Carbs were simple designs. Then TPI came along and I stopped thinking. Now I just drive. Try not to sweat why I’m able but I also assume I’ll always be able. Not the case with soot.

I’m hoping I do t end up with a Sooticon

https://journals.sagepub.com/doi/abs/10.1177/1468087418817447?journalCode=jera

 

[GARRIGA]

 

[CAC]

I can tell you that with this diesel the oil is staying pretty clean, just like my pre-smog 2007 and 2003 Cummins 5.9's did.

With my newer EGR/DPF equipped 2015 and 2017 Cummins 6.7's, oil is BLACK 10 miles after an oil change.

Definitely a reduction in soot loading.

 

[jeepoch]

EGR (Exhaust Gas Recirculation) in practice is primarily used to lower NOx (Nitrous Oxide) emissions. It does this by recirculating (reintroducing) some amount of exhaust gas back into the O2 stream of the piston's input cycle. Since the exhaust gas is now essentially inert (incombustible) it displaces a fraction of the volume of overall combustible oxygen entering the piston chamber. This then lowers the amount of heat at combustion, due to lesser amount of O2 that would otherwise typically be present. Nitrogen N and Oxygen O form NOx only at very high peak temperatures. Thus, the small amount of exhaust recirculated back into the air input lowers the combustion temperature which reduces (but not totally eliminates) NOx production.

And yes, I used to be a Chrysler Powertrain Software Engineer that helped developed the Engine Controller code to manage the EGR Valve.

Jay

 

[MeekoDiesel]

I hav no clue how one could prove that outside of asking an engineer who designed the system.

The HP and LP EGR systems are independent loops.

Once exhaust flows out of the manifold some enters the turbocharger and some is diverted back to the intake plenum via the HP EGR valve to go through the engine a second time. Before this diverted exhaust gas gets “burned again” it is cooled by the HP EGR cooler.

Exhaust that was sent through the turbocharger continues downstream and passes through the diesel oxidation catalyst / diesel particulate filter (DOC/DPF). It is at this point another portion of the exhaust is sent back to the air side of the turbo via the LP EGR valve, first passing through the LP EGR cooler, to be sent through the charge air cooler and into the engine again.


So, the HP EGR loop will contain post combustion soot particulates since some of these exhaust gases have not been passed through the DPF yet. The LP EGR loop gases will be much cleaner since they have been filtered by the DPF.

Summary: 2 separate loops, 2 EGR valves, 2 EGR coolers.

This engine does keep the oil pretty clean, mine didn’t start to turn black until after 5k miles.

Hope this helps!

 

[GARRIGA]

Sounds like soot still being retained albeit at a reduced amount.

 

[Plongson]

Jay, you appear to be someone that a a bit of inside info on these 3.0 diesels. Can you answer the question, where does the off-road gauge for engine temp get its information from (sender)?

I ask this because there is a substantial difference between what the off-road digital gauge reads and ANYTHING I can find using my FLIR IR equipment, scanning the coolant hoses, radiator, and ancillary cooling components...

For instance, the gauge will read 205°f and the highest IR readings on the front of this little motor are around 185°f. It's almost like it's near the coolant flow from the turbo.

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