Common Rail ?

[Renoram]

I've been around the CTD since '99 & have heard the term common rail off & on, but not paid much attention to it. Can someone explain what it is & any history &/or info associated with it ?

Thanks ahead

 

[SRadke]

Rather than a traditional mechanical injector pump which builds pressure up then pushes it through an injector for each individual injection event a common rail system uses a high pressure fuel pump that maintains a reservoir or "rail" of fuel at injeciton pressure all the time the engine is running. From thie rail a line travels to each injector which is opened and closed by a piezoelectric valve. This allows the ECM to control not only the pressure in the rail but also when and how long the injector is open.

 

[Renoram]

Thanks for the reply. What year(s) are considered "common rail" ? Is my '99 considered common rail using the VP44 as you explained ?

 

[Bob4x4]

Thanks for the reply. What year(s) are considered "common rail" ? Is my '99 considered common rail using the VP44 as you explained ?

03 and newer are common rail on the Dodge.



Bob

 

[Rescue Ram]

'03 and newer.

 

[SRadke]

The "common rail" term comes from the fact that one supply "rail" is used to provide fuel to the spray side and the drive side of the injector (they are supplied off of a "common" rail). It is the same idea as the Cat/Ford/Navistar design, except they (Cat/Ford/Navistar) use two supply rails, one rail for oil to drive the injector and one rail to supply fuel to be sprayed. It is a fairly involved deal, more than I want to try to explain. Just do a search and you should be able to find a "how it works" type of site to answer your questions.

Travis. .

Are you saying the HEUI system is considered a "common rail"? I've never heard that.

 

[Greenleaf]

I think so.....



Anyway, the Cummins N model was "common rail" years ago employing the PT system. (right?) The injectors were operated with their own individual cam lobe and push tube/rocker assy. The fuel supplied was under pressure however not near the pressure we see with the new engines. The injector would make the high pressure within it's self.



The amount of fuel the injector would deliver to the (combustion) chamber was/is directly related to the pressure the PT pump (supply) would deliver.



It's been some time since I worked on the Old 855 N series. I think I got that right. Just like it's smaller brother, the "B", they be one tough unit, overengineered.



Scott

 

[SRadke]

I'm a little confused about how your saying the fuel "drives" the injector. The fuel is at injection pressure but how does it "drive" the injector? I would say if anything the injector is driven electronically as that is the force that actually opens it.

 

[Vaughn MacKenzie]

The "common rail" term comes from the fact that one supply "rail" is used to provide fuel to the spray side and the drive side of the injector (they are supplied off of a "common" rail). It is the same idea as the Cat/Ford/Navistar design, except they (Cat/Ford/Navistar) use two supply rails, one rail for oil to drive the injector and one rail to supply fuel to be sprayed.

Travis. .

I don't quite follow what you mean. . . HEUI type systems utilize hydraulic drive at the injector, the common rail systems do not since the HP pump takes care of that task. The HP pump drives fuel straight into the cylinder, not to drive hydraulics. Common rail injectors simply turn On & Off, no hydraulic multiplication, drive, separate chambers, etc.



Vaughn

 

[TKingsbury]

Alrighty guys, you got me on this one . I did a search and did some reading and I am wrong. I guess the guy who taught the last electronic diesel class I went to was waaayyyy out in left field. Totally ignore what I previously posted, I deleted my posts to save any confusion for someone who may search and read this thread. Just goes to show you can't always believe what you read on an internet bulletin board. :-laf Good day gentlemen.

Travis. .

 

[nickleinonen]

The fuel is at injection pressure but how does it "drive" the injector? I would say if anything the injector is driven electronically as that is the force that actually opens it.

the HP fuel is actually what lifts the needle valve off the seat inside the injector body. all the electronic solenoid cartridge does is open a spill path for fuel, so the top side of the needle valve which has a larger surface area than the lower seat area looses pressure, and the needle lifts up and injection begins. there is no mechanical connection between the solenoid and the needle valve. i can get some drawings if needed to show what i am saying

 

[Vaughn MacKenzie]

No problemo Travis I hope the diesel class wasn't for diesel mechanics in training or anything important like that, LOL. . . sounds like the teacher could do a little research

 

[TJany]

HEUI- Hydraulically activated, electronically controlled, unit injector... that being said, HEUI injectors use motor oil at high pressure (the cats run 870-3200 psi if i remember correctly) now an oil pump pressurizes the motor oil and feeds it to each injector, and an electronic control solenoid allows the oil to "hit" the injector, multiplies the fuel pressure on the other side of the piston about 6 times, and increases the fuel injection pressure to as much as 24000 psi. common rail systems (to my understanding) utilize a high pressure rail, to electronically controlled injectors, the pressure is not developed in the injector itself like a unit injector. the electronic control simply allows the fuel to act on the injector needle, and the fuel pressure opens the injector, and the lack thereof (when the control closes) stops the injection period. the major difference between the HEUI and the common rail is where the fuel pressure is developed, one in a fuel pump supplying the rail, and the other in the injector itself



Tim

 

[TKingsbury]

No problemo Travis I hope the diesel class wasn't for diesel mechanics in training or anything important like that, LOL. . . sounds like the teacher could do a little research

Yup, it was a real class, a two day'er even. It was mostly about HEUI stuff. Someone in the class asked about the common rail and he gave a couple minute explanation on it. This was a while back though, and maybe he hadn't recieved new training himself. I dunno. The good thing I guess is that we don't have any common rail engines at work yet, so I didn't try to work on one and go WTF! Oh well, live and learn.

Travis. .