Question: Pilot timing considerations

[Mike_S]

I have been experimenting with ways of reducing smoke output on my lb7, in an attempt I tried disabling pilot injection, with a notable decrease in part throttle smoke. This is a good thing, however I don't enjoy sounding like an old 7.3 powerstroke.

Here is the question: anyone have any opinions on what the minimum duration between pilot and main injection could be before the injector and driver circuit doesn't have enough time to fire reset and fire again? I think with the right pilot timing smoke and turbo response could be greatly improved.

 

[baggedLB7]

Sub

 

[THEFERMANATOR]

Did you try the pilot timing correction spreedsheet for it yet? I know I used that and it cleared my part throttle up alot as well as quietened teh engine down.

 

[rcr1978]

Did you try the pilot timing correction spreedsheet for it yet? I know I used that and it cleared my part throttle up alot as well as quietened teh engine down.

Is that spreadsheet in a sticky somewhere? Would you post it if not? :angel:

Thanks

 

[THEFERMANATOR]

Is that spreadsheet in a sticky somewhere? Would you post it if not? :angel:

Thanks

It's in the timing calculator V3 sticky second from the top in this section. It's the equivelance ratio one.

 

[Mike_S]

Did you try the pilot timing correction spreedsheet for it yet? I know I used that and it cleared my part throttle up alot as well as quietened teh engine down.

i have not, truthfully, i was unaware this existed. LOL! I will look for that and give it a try.

however, my question still remains, if anyone knows or has an opinion on what the least duration between pilot and main can be before they iterfere with eachother or muddy up the injector signal. I suppose at some point it would become pointless to have both functional, probably mostly in the higher RPM, but mine disables above about 2200 anyways.

thanks for the input guys, keep it coming. :thumb:

 

[rcr1978]

It's in the timing calculator V3 sticky second from the top in this section. It's the equivelance ratio one.

Thanks, I never new one was even around.

 

[Mike_S]

Something worth reading

http://www.macchine.unisa.it/MECA01/papers/MECA01_paper06.pdf

 

[Mike_S]

Doesnt seem like anyone has much to say about pilot injection eh?

 

[xcablb7]

I've been waiting for to get my truck back from the body shop to do some experimenting, I have the same issues you have been trying to figure out, excessive smoke slow spool etc

 

[[email protected]]

I want to start messing with tuning stuff on my truck again but I have zero motivation and my laptop won't charge now so I have to plug it in now, but when I get ti e I want to read a little of that link you posted. Every time I change so ething on my truck I think its better then I change my mind and change it back and I don't have any numbers or organization to go by so I just get demoralized and go back to right where I was.

Anyway I think pilot injection and also fuel pressure can help slow spooling and smoke, but I still think my slow spooling and probably everyone else's is just due to how long it takes the Allison to downshift. It will be a different situation from a dead stop but while rolling you should be able to spool instantly because you should be able to downshift to red line and spool really fast.

 

[DIESELMAFIAPER.LB7]

heres another ? lol how the f do you use that thing i only glanced but wow im not good with excel so... also ive found pulling mine closer (only a few degrees) it seemed to help spool up and mine smokes a little still not bad though i can show you my pilot timing tables some time mike see if i can help or something

on edit: think i got the pilot timing calc figured nm but maybe ill have to talk to simon or josh bout the other stuff there

 

[Mike_S]

I have also come to the conclusion that pulling the pilot and the main injection event closer together seems to help out noticeably...but im still looking for the answer to the original question: at what point is the degree of separation too short for the injector to actuate, reset, and actuate again before it becomes inefficient or simply runs them together in a sloppy drawn out injection event?

 

[DIESELMAFIAPER.LB7]

Ya id say talk to a injector shop on that more then likely thry eoukd know how fast they can fire

 

[TopHat]

Here's a thought on how to determine how fast the injectors react. In the LBZ table for EFILive, B0720, look at, for example, the 20 MPa column. To inject 1 mm3 of fuel the stock value is 520.0 microseconds. To inject 2 mm3 of fuel, the stock value is 538.0 microseconds. It seems to me you could interpret that this way: After the injectors are open, it takes 18 microseconds to get 1 mm3 of fuel at that pressure. So, subtract 18 microseconds from the first value, 520 microseconds, and you get 502 microseconds as the "dead time" that it takes to open and close the injector. That is the figure you need to play with the pilot timing. Does that make sense to anybody besides me?

The only problem is that it doesn't seem to hold exactly throughout the table. But around 500 microseconds, give or take, seems to be about right for the lower pressures. They get faster at the higher pressures, maybe because the fuel pressure itself helps to open the injector?

 

[[email protected]]

Since you have an lb7 how much tuning have you tried on the maf limiting table

 

[xcablb7]

.Higher pressure will deliver the same amount of fuel i.n a shorter period of time. I'm not sure anyone knows how long it takes for an injector to go from open to close and back open, but I would look at the smallest pw in the pilot table then calculate how many microseconds your desired timing takes at a given rpm, make sure your calculated number is greater than any factory used ms and id say your safe.

 

[[email protected]]

The sae paper seemed to say that pilot injection timing did not have much effect on anything, and that the quantity was more important. I just don't get how less pilot timing could make less smoke assuming the main injection and everything ee was constant? Unless the a too early pilot was causing a lean condition that makes the main not combust as good. During spoolup I could see a early and big quantity pilot helping combustion in a chamber with a really rich mixture, I think the large quantity of fuel injected might have a surprising effect on the cylinder temps pre combustion.

 

[xcablb7]

We don't exactly have control over the actual pilot timing just the pw, quantity, and degrees between pilot and main, the pcm computes where it need to start the pilot based on time it needs to spray the pw commanded and delay to the main injection. I have logs that prove this out showing almost 60* of pilot timing

 

[Kspen90]

This seems to definitely be worth some thought