EGR ops NCV3

Would someone explain to me and perhaps others how the EGR valve works. What happens when you start the engine, put it in gear, accelerate from a stop, drive down the highway, red lights, shut the engine down, etc. What does it do when warm, when cold? What is it doing specifically when it continues to run after the engine is shut down and on and on?

Any and all information would be appreciated.

gary

Simply, I can't think of 1 living or mechanical form that benefits from having it's own waste shoved back down it's throat, exhaust gas recirculation. I will try to keep it more positive after this post.

The EGR valve (Exhaust Gas Recirculation) is a valve that controls the flow of cooled exhaust back into the engine's intake of air. It is an emission device designed to help control the levels of NOx (oxides of nitrogen) the engine emits out the tailpipe by helping to control the combustion temperature inside the engine. The valve controlled by the ECM meters exhaust back into the engine based on load and speed parameters. At idle, there is not a lot of EGR, as combustion temperatures are low, at part throttle and regular cruising down the highway, EGR rates are at their highest as there would normally be an overabundance of combustion air vs the fuel (in a gas engine you would call this lean). At these "lean" conditions the formation of NOx would be at its highest, hence the high rates of EGR. At wide open throttle, the EGR rate is more a function of engine speed. As engine RPM increases under full load the conditions that lead to NOx formation slowly start to decrease and EGR rates are lowered as they are not needed and, they become detrimental to performance. It should be noted, to those of you who monitor your exhaust temps, exhaust temperature is not a good indication of combustion chamber temperature (where the NOx is generated). The resistance to "force" the exhaust back into the intake (which is under pressure "boost") is provided by the variable geometry turbo charger we have. Not only does the ECM use this to get more boost at low RPM, it also uses it as a restriction to keep the EGR system at a higher pressure than the intake (so the exhaust will flow in). At shut down, your EGR valve goes through a series of fully closed to fully open cycles to try to knock off any soot or crud that may have built up. This build up is what is believed to be the direct cause of all the EGR related issues. As discussed, the H44 recall extended the time that the valve performs this "cleaning" cycle.

Of note also, your engine also has an intake throttle (yep, just like a gasser!) that the ECM uses to make the combustion super rich to elevate the exhaust temperature to cause the DPF to burn off or "regenerate". In this state, combustion temps are quite low but the exhaust temps go sky high as there is a LOT of combustion actually happening in the exhaust system! This is why you see the funny tailpipes on newer Duramax and Ford diesel pickups, it is an attempt to cool off the exhaust exiting the truck during a regen event. My guess is the smaller scale of the Sprinter and the longer exhaust system negates the need for this for our vans.

Hope that answered your question....

I was curious when the DPF does a "regenerate" would the driver experience this when its happening such as a different exhaust tone etc? I noticed with mine at times i hear a unusual noise which kinda sounds like a muffler with a exhaust leak, will make this noise 2-3 times a month for about 5 min or so i would assume its the DPF cycle? Other than that i have learned to ignore it. Performance during these times i notice is slightly more temperamental.

There is a strong possibility this is what you are experiencing. The regen process would give you a wee bit of odd performance (intake being throttled down a bit) and the sound could be the extra "fire" going on in the exhaust system to cook out the DPF. The fact that you notice it tells me you and your Sprinter are close friends.

Thanks for reply...yes my sprinter and i are good buddies we travel together every ware

Piper

Let me give you your first Thank You in one post.

gary

Jon

Just post SOMETHING so I can Thank you. :

gary

Passive regen happens every 700 miles or so on my Sprinter, as indicated by the Engine Control Module data read by StarMOBILE.

I've never noticed passive regen happening, though. The only time I "witnessed it," was while driving from Seattle to Portland, OR. I knew when the next regen was scheduled - just on the other side of the Oregon state line, so I was was glancing at StarMOBILE's output. EGT hit 700+ degrees Fahrenheit, but if I hadn't been glancing at the screen regularly, I'd have missed it cuz I never hear, smell or feel it. I think my factory cargo partition with the factory heavy felt lining, is a really good sound barrier... or I'm deaf.

Passive regen consumes a litre of fuel, but I don't know how long it lasts according to the ECM info.

I know that it is not possible to pump more than 34 liters per hour through the factory fuel filter and you can't do that for more than about 10 seconds. I saw 33, but I never saw 35.

Do reach this level of fuel consumption, it requires a steep grade (+15%), several hundred lbs of payload as well as a fully actuated acceleration pedal from a dead stop. Only then will the driver approach the 34 litres per hour fuel consumption rate.... and it backs off rapidly back to the teens when velocity's achieved... what it does from there, well, I had to drive and stop looking at the screen.

So if 33 litres per hour is the most you can stuff down the fuel filter and if regen consumes 1 litre, you're looking at 2 minutes or so for a DPF regen, as a minimum amount of time it could possibly take, right? Is my math incorrect? Or am I failing to consider something critical to accurate calculations? Say it goes 1/2 the potential fuel volume... that'd be four minutes, which would come close to Shanemac's 5 minute estimation.



-Jon

The extra fuel is not a constant throughout the re-gen process, not 100% sure with the Sprinter, but most diesels use a gulp of fuel to "light up" the DPF and then the air intake management is the primary source from then on to manage the burn with extra fuel being the secondary. The re-gen process is also done based on a pressure differential in the DPF, so Shane may have a longer re-gen event than Jon as Shane is in a much colder climate and the temps required for re-gen would be harder to maintain.