Alot of confusion has been brought on by the new aftertreatment system. While this is only a brief rundown of how the system operates, this should give you some info.


The catalyst and aftertreatment diesel particulate filter are made of ceramic material with the chemical coating that is used to oxidize particles of unburned fuel and oil.
The ceramic substrate is held in place in the stainless steel canister by a mat, which is a high-temperature pad that surrounds the ceramic substrate with the metal muffler housing.
The aftertreatment diesel particulate filter captures the particulate matter in the exhaust, and then uses the heat generated by the ratio of the unburned fuel and oil particles in the catalyst to oxidize the particulate matter.

The aftertreatment diesel particulate filter removes soot particles from the exhaust by passing the exhaust gases through a ceramic filter. The soot is oxidized in the filter to form invisible carbon dioxide, giving clean exhaust at the tailpipe. Ash is a by product of oil consumed during normal engine operation. Ash collects in the aftertreatment particulate filter and requires periodic cleaning. This system is designed to decrease the exhaust particulate emissions from the vehicle tailpipe.

The aftertreatment system is monitored by the engine's ECM through the use of exhaust gas temperature sensors and a pressure sensor. The pressure sensor is used to monitor the soot/ash loading of the Cummins® particulate filter to determine if:
1. A regeneration event is needed.
2. Maintenance is needed.
Regeneration is the controlled removal (cleaning) of particulate matter (soot) deposited in the diesel particulate filter. There are three general types of regeneration:
1. Passive regeneration is the continuous regeneration when operating conditions maintain sufficient exhaust temperatures. Soot is continually oxidized in the Cummins® particulate filter to form carbon dioxide. Passive regeneration is totally transparent to the driver.
2. Active regeneration occurs when there is not sufficient heat in the exhaust. Exhaust temperatures are raised by injecting a small quantity of fuel upstream of the diesel oxidation catalyst. The resulting chemical reaction over the diesel oxidation catalyst raises exhaust gas temperature high enough to oxidize the carbon from the filter.
3. Stationary regeneration is the oxidation of soot while the vehicle is not being driven. It is performed because the normal driving cycle will not support passive or active filter regeneration.
A few duty cycles (high idle time and short route segments) will occasionally require a stationary regeneration, such as:
Urban pickup and delivery applications
Emergency vehicle applications


As we can see here, high idle time will become more of a factor than ever. If the DPF cannot clean itself, the ECM will go into an active regeneration and inject a small amount of fuel from the engines injectors into the DPF to raise EGT.

Other engine companies are using a seperate injector mounted downstream of the turbo. However Cummins, chose to use the actual in head injectors to deliver the dosing of fuel. It hasnt been out long enough yet, but I really dont like the use of the in head injector opposed to a seperate doser injector.

 

Good info thanks.....

 

Other engine companies are using a seperate injector mounted downstream of the turbo. However Cummins, chose to use the actual in head injectors to deliver the dosing of fuel. It hasnt been out long enough yet, but I really dont like the use of the in head injector opposed to a seperate doser injector.


Very interesting information. Why don't you like the head injector idea as much?

 

I'd guess that a failure in the fuel routing with the Cummins system could result in poor running, due to lack of fuel and or fuel pressure at the injector, whereas a dedicated particulate injector could be designed in such a way as to not affect the rest of the system in the even of a failure.

 

Would a "dedicated" system have its own fuel pump?

 

Does anyone know what kind of EGT temperatures are involved with the cleaning cycle? Seems the use of the in head injectors raises the temp of everything between the combustion chamber and the DPF. I like a seperate injector at the DPF.

 

I view that as a plus rather than a minus. Less pieces, less complexity, less things to go wrong. Cummins already has 3+ years experience using the in-head injectors to trigger a cleaning event and it seems to work pretty well. Just stretch the 3rd event a little and the fuel is in the system to make it work.

 

No, a dedicated system uses the engine fuel pump as a carrier of pressure and simply uses a series of sensors and electronic valves pulse width modulated to control the fuel being sent to the DPF. CAT, Detroit, and the ISM and ISX all use this system.

Cat has the biggest difference since they use a spark plug mounted in the downpipe to start a flame about a foot down the downpipe to raise EGT temps in order to regen. They also use a seperate injector.

Detroit and MB use an intake throttle valve pulse width modulated to restrict intake air flow in order to raise EGT's. The also use a seperate injector.

The main reason I do not like the idea of in head fuel injectors is the possibility of a burnt valve (open exhaust valve + fuel). Cummins is using a seperate injector on the ISX and ISM, but uses the in head injector on ISB, ISC, and ISL.

I hope it works out well for them. As no_6 mentioned, it would be less complicated.

 

How does the in-head injector scheme for the diesel particulate filter's active regeneration cycle affect the 6.7's power production? I'm guessing the quantity of fuel injected for the lengthened 3rd event is insignificant.

 

Im not sure as well, but I would bet you are right. Hopefully I will know something about that later to come. When I got the certification on the ISB, C, and L, it did not cover which phase of injection it used to dose the DPF.

 

According to the October 2006 Master Tech Reference Book, it says this:

"Another type of regeneration is Active Regeneration. Active Regeneration occurs when the exhaust temperature is not hot enough to enable particulate matter regeneration. The ECM commands the fuel system to introduce unburned fuel into the exhaust stream which creates heat and allows regeneration."

Are you sure it goes in through the head? The way that reads to me is it is introduced downstream of the head, I don't know for sure, but that is the way it reads to me.

 

No, there are no other fuel injecting devices aside from the fuel injectors themselves on the ISB, ISC, and ISL. The ECM commands the fuel injectors to supply fuel when the exhaust valve is open and supply the fuel to the exhaust stream to the DPF. Since the common rail uses smart injection via solenoid, the ECM can control at any given time when to inject fuel.

 

Hope you don't mind me bringing this topic back up, but that was a great post Monty. I snipped it to my question:
If you are towing heavy, say up a mountain grade, will the higher exhaust temps perform this passive regeneration?
Sake of argument, I load my camper and drive up a hill for 15 minutes with maximum boost once a month, will that clean it enough so it will not need an active regeneration?
This would make a great excuse to go camping more often.

 

The DPF needs temps in the 1022 deg F range for active regeneration.

The hottest I have been able to measure in the manifold during a regen process was in the low 1300's.

Remember that the Cat actually heats the exhaust temp up before it enters the DPF so it does not have to be quite as hot as you might think upstream.

 

Passive regeneration is happening anywhere from 480 degree on up to 800 degree's
Active regeneration is happening from 580 degree's on up to 1200 degree's
Hydrocarbon will not be introduce to the Aftertreatment till approx. 600 degree's at the DOC inlet.
Generally during active regeneration the temps at the DOC inlet will be around 600 to 650 degree's and before the DPF inlet it can be high as 300 degree or more difference from the DOC inlet temp. and the DPF outlet will be slightly higher than the DPF inlet.

The DPF does depend on the DOC to put heat along wiith Nitrogen Dioxides (more than one atom of oxygen) into the DPF for oxidizing temperature

The higher the temperature , the oxidation of soot happen quicker.