when is Pilot Injection active?

[larski156]

This is my first go round with a LBZ. Iv done the LB7 and LLY a few times and have had pretty good success with them both. I have eliminated the post injections on the LBZ by setting the max number of injection events per cycle to 3 in table B1021. That seems to be the only table i can find that has anything to do with deciding which injection events are going to occur. What actually tells the ECM what injection events to preform when. I assume that setting it to 3 will eliminate the 2 post injections. Will setting the table to 2 shut off the Pilot #1 or Pilot #2? The whole table is set to 3 injection events max but i know that at 5k RPM the injectors cannot preform 3 injections per cycle. somewhere something has to be setting when pilot 1 and 2 are and are not active.

What i want to do is raise the fuel pressure to 120 MPa or better in the cruising range and spray 2 very short pilots. Then advance the pilot 1 before main injection (somewhere around 40 BTDC) and space out #2 so its PW ends about 18-22 CAD before main injection occurs. I have discovered a slight MPG gain on the LLY by limiting the PI PW and spraying it about 20 degrees in front of the main injection. I think if i could split my PI into two even smaller events there may be gains to be had. Of course its going to be a little louder and my NOx emissions are not going to be the greatest.... minor details.

[CwF]

As far as I can tell my LBZ really only as 1, 2, and 3 as effective settings in b1021. Setting to the minimum 1 is the main, setting to 2 adds pilot #1, setting to 3 add Post #2. Pilot 2 and 3(?) and Post #1 is unavailable due to unknown factors I think we have no access to. I tested this awhile back and settled on it. I do understand your point but I believe the method to be unavailable. Consider this though: All events add together to CALC and Post #2 is just a name, and can be one of the events you are asking for. We do have decent control of Post #2 after 1700 rpm with timing and amount. You can literally cut the main in half, or more and tighten up the post timing to within 9-10° (I use 938 μs) of the conclusion of the main. I'm not that aggressive but have found that the post seems to help with rail dynamics and maintains pressure a little better in the upper (mid) range - and I don't have enough data to say that for sure but it is my wishful thinking. Look at that maybe? Below 1700 rpm is where I assume your looking to do this? You are looking for a faster rise time BTDC? Are you beyond 100% timing, should be? And with 2 pilot events would you then allow the main duration to extend past TDC?

And a pet peeve of mine I keep seeing is the assumption the system freaks out at higher rpm and the the injection goes into OMG mode if you ask it to attempt multiple events at 3k or whatever. The great engineers in the world keep working on this issue and they know that the advantage of multiple events is in now way related to rpm. What is related to rpm is physical capability and the allowed time to get it done, or to say practicality concerns. As pressure ramps up, duration shortens, and a window is opened. The delay of the injector is addressed with piezo, etc. The advantage is there, if technology figures out how. The main issue with a duramax is its volume and the volume we're trying to inject. A larger injector for example effectively shortens the duration for a given volume yet may introduce greater refresh delay between events, and if at max pressure = there ya go, the practical limit. Imagine for a moment if you wanted 400hp at 5000 rpm.... The fuel amount is much lower and my guess is there is a big enough window for all three events. At 700hp+, not a chance.