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      05-26-2012, 07:47 AM   #1
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very limited injector duty cycles and injector timing.......

I want to discuss the very limited IDC's that are inherent to DI motors. From what I can gather from napkin calculations there is very limited time between valve closing events and the ignition event. With trying to use E85 and raising the duty cycles, what is the maximum available time for this? If we reach the fuel pressure max, and then the duty cycle max, the only alternative are larger injector but I don't think anyone is making them for the N54 yet.

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      05-26-2012, 09:12 AM   #2
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If we reach the fuel pressure max, and then the duty cycle max, the only alternative are larger injector but I don't think anyone is making them for the N54 yet.

T
That's a big IF. I can't remember what the BMW engineer quoted as a flow rate on the injectors, but it was something huge. The injectors were sized to run the engine on just the low pressure fuel pump - 5 bar - while the HPFP runs anywhere from 50-150 and is rated up to 200 bar.

The N54 community is just recently running high concentrations of E85, so there are no long term reports of fuel pump durability, seal or hose issues, or any known fueling limits. Vishnu has been doing at least 500RWHP with no meth on 91 octane on their single turbo while showing very conservative AFRs in the 11-12 range. This does require some form of fueling upgrade. While they're still not publicly announcing what the upgrade entails, we speculate it's on the low pressure delivery pump end.

Additionally, isn't DI capable of continuing injection well into the compression stroke long after the intake valves are closed? So it has more than one stroke of time to inject fuel - as soon as you start the intake stroke, past the intake valves closing, and partially into the compression stroke.
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      05-26-2012, 09:55 AM   #3
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Yeah, I suspect that people like Shiv have been able to push as much fuel as they have through the stock injectors because it was designed to flow 300+hp worth of fuel in an extremely short period of time, maybe just a fraction of the compression stroke. Even if we ask it to start flowing way back during the intake stroke and continuously through the compression stroke it probably works fine. Maybe not as good for pristine emissions, but good enough for big power.

I'm still curious to see what tricks Shiv had to do, though. My guess is that there were one or more limits in the software that had to be worked around, and then maybe we do something like ask for even more pressure from the pumps. But I don't know. Seems to be working. It'll be amazing of there's enough excess capacity to run 100% E85 even at very high power levels.
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      05-26-2012, 10:07 AM   #4
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The area I am interested in is >5000rpm. This time is very limited for injection events and with E85 additional fuel volume needed over the 91aki the system was designed for, there are limits with the DI injectors that will be reached. There just isn't enough time for copious amounts fuel to be atomized for proper burn structure to support huge HP numbers with just the DI system. There will have to be additional fueling up stream.

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      05-26-2012, 10:47 AM   #5
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IIRC i read a while back that the stock IDC is roughly 40% of the available injection window at 7Krpms. That gives us quite a bit of room to play with. Also, based on what i've read there is a MAF "bug" that limits fueling to roughly 500whp worth of fuel, however that bug is fixable has been done.

FWIW, Cobb uses stock fuel rail pressure even on the ~400whp stage 2+ maps. Its all IDC manipulation, and IMO that's more evidence that theres a lot of headroom there when you start playing with rail pressure and IDC.

Since the DI is common rail the DME can command injection even when the intake valve is closed. So, if need be the injector can start spraying just before the valve opens and continue through the whole time the valve is open. The main question to me is if the HPFP can supply enough flow in that scenerio.
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      05-26-2012, 11:05 AM   #6
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Taken from another forum

"DI has the benefit of more accurate fuel placement and timing, which creates more horsepower even while using less fuel. However, it does bring about a new limitation. Rather than being able to spray fuel at any time, DI is limited to a window that is less than 40% of the engine cycle. The reason for this is simple. First, you cannot start spraying fuel until the exhaust valve has closed. If the exhaust valve was still open, then fuel will spray right past the valve and burn in the manifold. While this strategy can be combined with retarded ignition timing to help spool a large turbo, it cannot promote proper combustion when revving through the power band. Next, the DI injector must close with enough time for the fuel to travel where it needs to be before the spark plug fires. Spraying fuel too late in the cycle results in poor combustion and even misfires. Horsepower will typically decrease if the injector duty cycle is pushed past 40%, although this number varies based on the actual open and close angles utilized."

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      05-26-2012, 11:12 AM   #7
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Yes, but that's referring to the power and exhaust strokes. I'm talking about just the intake stroke. There is some valve overlap but IDK what that is/can be when adjustments are made by VANOS.
This is a very interesting discussion and i wish more informations was available.
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      05-26-2012, 11:37 AM   #8
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Quote:
Originally Posted by rader1 View Post
Yes, but that's referring to the power and exhaust strokes. I'm talking about just the intake stroke. There is some valve overlap but IDK what that is/can be when adjustments are made by VANOS.
This is a very interesting discussion and i wish more informations was available.
No it is explaining when the injection event can occur for maximum power. It has to happen after the exhaust valve closes. You don't want to waste any fuel with the limited amount restricted by time already.

At higher RPMs the overlap is reduced with vanos.

We need someone to do the math on the avail time vs IPW time vs IDC
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      05-26-2012, 12:39 PM   #9
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If you are so concerned with it, why not get an oscilloscope and start checking injector duty cycle versus crank rotation?

The injection cycle is shortened to about 40% of a port injection motor is what I read in that. Obviously the exhaust valve needs to be closed, and the injection time needs to stop sometime before BTDC. A port injector can feasibly be open 720 degrees, but obviously not ideal. 720x40%= 288 degrees. At 7200RPM that's about 6.7ms.
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      05-26-2012, 12:56 PM   #10
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Quote:
Originally Posted by JamesM3M5 View Post
If you are so concerned with it, why not get an oscilloscope and start checking injector duty cycle versus crank rotation?

The injection cycle is shortened to about 40% of a port injection motor is what I read in that. Obviously the exhaust valve needs to be closed, and the injection time needs to stop sometime before BTDC. A port injector can feasibly be open 720 degrees, but obviously not ideal. 720x40%= 288 degrees. At 7200RPM that's about 6.7ms.
Well I guess 'concerned' may be the wrong word.

Does anyone have the flow rate @ Xpsi for these injectors? Since the FP is variable and the HPFP is limited, is there a flow rate plot for these injectors?

Just trying to see what the calculated limits are for fueling.

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      05-26-2012, 07:24 PM   #11
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You could estimate the current injection window by logging ipw and idc with Cobb. Include vanos and if you had the cam specs you could get very close to actual open/close points.

I would think the full window is only during intake stroke at this time... Of course it could be lengthened with programming.
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      05-26-2012, 08:32 PM   #12
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Quote:
Originally Posted by Joshboody View Post
You could estimate the current injection window by logging ipw and idc with Cobb. Include vanos and if you had the cam specs you could get very close to actual open/close points.

I would think the full window is only during intake stroke at this time... Of course it could be lengthened with programming.
Yes but not knowing the fuel rate at Xpsi from the HPFP we won't know BSFC. This is is the majic number we are after.

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      05-26-2012, 09:18 PM   #13
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Quote:
Originally Posted by Mangler View Post
Well I guess 'concerned' may be the wrong word.

Does anyone have the flow rate @ Xpsi for these injectors? Since the FP is variable and the HPFP is limited, is there a flow rate plot for these injectors?

Just trying to see what the calculated limits are for fueling.

T
Searched for a bit and am surprised that I can't find any experimental flow bench testing for our injectors. Is there a reason why data doesn't exist? I know HPF has some nice equipment for this. I'll donate a lightly used injector for testing.
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      05-26-2012, 09:43 PM   #14
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Searched for a bit and am surprised that I can't find any experimental flow bench testing for our injectors. Is there a reason why data doesn't exist? I know HPF has some nice equipment for this. I'll donate a lightly used injector for testing.
HPF has equipment for testing normal injectors. Our injectors are a totally different breed.
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      05-27-2012, 06:55 PM   #15
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