Julian

iTrader: (14)

I got my rebored injectors back from RC Engineering and I had them measure flow rates at 60,80,85 and 100% duty cycles.

Interesting.. the 550's are very linear at 550 and at over bore to 650. However the 850's are very non-linear above 80% duty cycle. I would attach a plot but I cannot create a .pdf on my home computer.

This phenomena may explain two separate tuning issues.

1) some people have success with 850's in primary positions other do not. The non-linear fuel rate will make it hard to tune unless you bad idle tuning on the linerized full flow using the low duty data. i.e. claim that injector is smaller than full flow data.

2) using 100% duty flow data on secondary's without tuning ot AFR's will lead to lean mixtures at normal running duty cycles with 70 to 80% being leanest positions; i.e target max power positions.

I am thinking of inputting 80% DC flow rate divided by 0.80 as my input flow rate. This would give effective size of 1080 cc/min (864/.8) vs. measured 1223 cc at 100%

60% (#1/#2) 80% 85% 100%
550 Original 321 321 426 423 460 458 552 553

-0.84% -0.84% -1.30% -2.00% 0.30% -0.13% 2.31% 2.50%
850 Original 400 405 550 552 611 615 851 855
-9.10% -7.97% -6.26% -5.92% -1.99% -1.35% 16.03% 16.57%


550 (650) 373 371 499 497 539 535 656 650
-1.61% -2.13% -1.28% -1.67% 0.36% -0.38% 3.83% 2.88%

850 (1220) 510 517 767 773 864 868 1219 1227
-16.26% -15.11% -5.55% -4.81% 0.14% 0.60% 20.09% 20.88%

dgeesaman

iTrader: (7)

That's strange. The point behind duty cycle is exactly to maintain linearity.

Could their testing rig have tailed off in fuel pressure?

Julian

iTrader: (14)

My elementary understanding of DC exactly. Open half the time .. half the fuel goes through. As to testing pressure, if it did drop off then curve would drop as DC increased not raise; and I do not see pressure raising with more flow even on a bad rig. My only off the cuff explanation is that as since duty cycle is really time of opening not amount of opening of solenoid i.e 100% equal s open all the time and 50% equal s open 1/2 the time that one must factor in the rate of opening and closing. Say opening and closing event takes 2 msec, thus average flow over this time period is 1/2 full flow. At 100% the time is so long open that the open/close tails have no effect on total output, however at 50% duty cycle injector is continuously pulsing on and off thus a significant time is spent at partial flow, some of this may be compensated by lag time. some may not. I am now sending injectors of to Yaw Power for more testing.

Julian

iTrader: (14)

quoted from Yaw Power site;

Basic Injector Operation
To find the flow rate of the injector, we can supply pressurized fuel at the inlet, apply voltage to the coil, and measure the amount of fuel that flows through the injector in a given period of time. This is called static flow testing, and the result is the static flow of the injector at the stated test pressure.
This type of testing has some validity in the sense that we can clearly show that one injector flows more or less than another, but its ultimate usefulness is limited.
Once we install the injectors on the engine, we will not be holding them in the wide open or static position, we will be cycling them on and off rapidly. This is a dynamic situation, and the dynamic injector characteristics are far different than what the static flow test may predict. For this reason, static flow testing has little value to the experienced tuner.

To gain a better understanding of an injector’s dynamic flow characteristics, consider the following.
Let's say that we perform a static flow test on an injector, and find that it flows 100cc's in one minute. This information is valid, but it tells us nothing about the dynamic characteristics of the injector.
Consider what happens if we turn the injector on and off at a high rate of speed, let's say 100 times per second, and measure its flow for that same period of one minute. Obviously, the measured flow would be less than the static flow, because the injector would only be flowing fuel for a portion of a minute.
To be more exact, let's say that while the injector is cycling on and off, it spends equal amounts of time turned on, and turned off.
In this scenario, the injector would be described as running at a 50% duty cycle, which simply
means that it spends 50% of its time in the on state. (More on this later)
In theory, our measured flow should equal 50% of the static flow, since the injector is turned on 50% of the time, right?

Wrong! Why you ask? As usual, when theory meets practical application Mother Nature rears her ugly head, and the immutable laws of physics get in our way.
In practice, we find that three very important things happen which result in the measured flow being less than what we estimated based on our static flow numbers.
The first is that the magnetic field which pulls the pintle off the seat takes a finite amount of time to build. While this magnetic field is building, the pintle is sitting still on its seat, and so we have an injector with voltage being applied, but absolutely no fuel flow!

Once the magnetic field becomes strong enough to pull the pintle off its seat, we run into issue number two, which is the fact that the pintle is in no big hurry to move! Instead of snapping immediately to its full open position, it lazily moves from the fully closed position (No fuel flow) to the fully open position. (Full fuel flow)
Instead of having an injector that is on 50% of the time, and off 50% of the time, we have an injector that spends a portion of its on time flowing no fuel, another portion of its on time at partial flow, and the final portion of its on time at full flow.
As a result of all this, the actual fuel flow from our injector will be less than that predicted by static flow testing.Injector

For a good read go to: http://www.yawpower.com/spreadsheets.html and open "Injector Dynamics Sample"

Julian

iTrader: (14)

As a followup to this. Yaw Power does not have the setup to test OEM side feed injectors, after many months of thinking they could build a jig and then getting behind on other work I finally got my injectors back untested. So back to the non-linear flow in 80 to 100% duty cycle region, what to do?