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Author Topic: Let's start with the Basics... KRKTE  (Read 19749 times)
NOTORIOUS VR
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« on: August 23, 2011, 01:22:51 PM »

Ok... so I've been doing some reading, and calculating, and more reading and more calculating and I've come to the realization I don't know jack shit, because what I thought I knew doesn't add up (literally).

Let me explain.

My car drive's OK with a KRKTE @ 0.048 LTFT's are around 3-4%... it's where I was told a while ago that is what my KRKTE should be with my injectors (1000cc @ 3 BAR, running stock 4 BAR they're approx 1168cc or so).

Fine..

Stock S4 injectors are 33#/hr or 349cc/min... great.... M-box KRKTE is 0.147... right... moving along...

to Caluclate KRKTE according to the PDF:

KRKTE = 50.2624 * Vhzyl / Qstat

Vhzyl = 0.450

Qstat is the flow rate of your injectors using n-Hep in g/min.  No idea at what pressure though... 3 bar, 4 bar, 10 bar no clue.

Right so, stock injectors @ 4 bar are 349cc let's add 5% for n-Hep and then convert to g/min... so we a Qstat for the stock injectors @ 3 BAR = ~217 g/min  at 4 BAR ~239g/min

Plug that into our known equation above from the PDF and we get something completely different from the M-box value.

@ 3BAR, KRKTE = 0.10423
@ 4BAR, KRKTE = 0.09463

My injectors @ 4BAR the KRKTE would be approx. 0.02692

What gives, and what am I missing here?
« Last Edit: August 25, 2011, 05:26:34 AM by NOTORIOUS VR » Logged

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« Reply #1 on: August 23, 2011, 02:00:59 PM »

There is something funky with that PDF, but lets ignore that for the moment.

I believe the stock injectors are 349cc/min (249g/min) at 4 bar (not 3 bar)

Still.

50.2624 * .450 / 249 = .0908, which is quite far from stock.

 

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TTQS
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« Reply #2 on: August 23, 2011, 02:01:58 PM »

Just a very quick thought as I'm off to bed but it's probably an issue with the units of measurement. A quick look at the DAMOS shows that the unit of KRKTE is milliseconds/% Load (I presume) so the figure of around 0.1 looks correct because it gives an injector on time of ca. 20 milliseconds at full load with the example Qstat values you supplied.

Also remember that the PDF we all know and love is for the 132 kW 1.8T 20 valve project, not your 2.7 twin turbo S4.

Doug
« Last Edit: August 23, 2011, 02:07:34 PM by TTQS » Logged
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« Reply #3 on: August 23, 2011, 02:06:43 PM »

What units is 50.2624?

If we had that, I think we can fill in the rest to get it to msec/% by just doing unit analysis.
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« Reply #4 on: August 23, 2011, 02:29:45 PM »

Ok. Lets try this again.

100% load is 0.4452 liters of air at standard density

That's 0.5455 grams.

At 14.7 AFR, thats .0371 grams of fuel

For an injector spraying 249 g/minute, thats 8.94ms for 100%, or 0.0894ms/%

EDIT: my half cycle thing is junk.

It should be 0.0894ms/% or 0.0897ms/% assuming reference air density of 1.2293

(1.2293 kg/m^3 * .4452 liters / 14.7) / 249 g/minute / 100 in ms =

with 1.05 correction, thats still 0.0934

Sigh.

« Last Edit: August 23, 2011, 02:58:01 PM by nyet » Logged

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TTQS
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« Reply #5 on: August 23, 2011, 02:30:20 PM »

I can shed very little more light on it except that when I plug in the numbers quoted in the funktionsrahmen, I get 47.813 instead of 50.264. This figure is just the air density in g/dm^3 divided by the product of a bunch of constants, i.e. 1.23 g/dm^3 100 x 14.7 x 1.6666E-5 x 1.05.

The only other thing I could think of is that the air density is quoted at 0 degC/32 degF if the funktionsrahmen is to be believed. This is a bit odd since most values are taken at STP, which is 25 degC if I remember high school physics/chemistry correctly. If KRKTE is internally corrected by the ECU or externally corrected by a tuner, this could explain a difference, but that would tend to lower KRKTE a little bit, not increase it.

I just looked at a DAMOS for the S4 2.7T and KRKTE is 0.09778 ms/%Load, so I'm not sure where you're getting 0.147 from.

Doug
« Last Edit: August 23, 2011, 02:37:38 PM by TTQS » Logged
judeisnotobscure
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« Reply #6 on: August 23, 2011, 02:47:34 PM »

on any stock 2.7t s4 file the krkte is set to 0.147
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« Reply #7 on: August 23, 2011, 03:03:44 PM »

Maybe we've been starting with the wrong stock injector size all along?

Perhaps 33lb @ 4 bar is wrong?
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« Reply #8 on: August 23, 2011, 03:27:08 PM »

Ok. Lets take a different approach.

The Audi P/N for the grey tops is 078 133 551 M
Google says the corresponding Bosch P/N is 0280150921

Now, I get a bunch of different flow results for 0280150921 on google.

this says 156cc/min @ 3bar, or 208cc/min @ 4 bar

suggests 168cc/min @ 3 bar, or 224 cc/min @ 4 bar

There is something very fishy going on.
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s4rmm
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« Reply #9 on: August 24, 2011, 12:45:51 AM »

on any stock 2.7t s4 file the krkte is set to 0.147
No, it's 0.09768 as Doug wrote, checked G and M-box.
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TTQS
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« Reply #10 on: August 24, 2011, 12:59:01 AM »

I checked an RS4 2.7T DAMOS and KRKTE is 0.06756, so that's quite a bit lower. The spec. said 380 bhp for that file so some evidence there that the higher power tunes have lower KRKTE and injectors with larger Qstats will obviously reduce KRKTE, as we know.

or 224 cc/min @ 4 bar

A Qstat of 223 g/min corresponds to the funktionshrahmen constants, a Vhcyl of 0.4552 litre and a KRKTE value of about 0.0976 so that all ties up. I checked Elsawin and the AGB & AZB engines do indeed have a 4 bar FPR. Checking up on the spreadsheet from www.mksautobusiness.fi gives the following injectors designed to operate at 4 bar and 223 g/min (Bosch part numbers):

0280155899
0280156052
0280157004
0280157005

The other issue to be aware of is to make sure we're not confusing g/min with cm^3/min because with the density of gasoline being about 0.75 g/cm^3, that will make a significant difference to a calculation.

Doug
« Last Edit: August 25, 2011, 01:29:50 AM by TTQS » Logged
NOTORIOUS VR
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« Reply #11 on: August 24, 2011, 06:45:30 AM »

on any stock 2.7t s4 file the krkte is set to 0.147
No, it's 0.09768 as Doug wrote, checked G and M-box.

Interesting... I just checked the A6 R box and it is 0.09783 as well.

Checked S4 2.7T H-box: 0.17216
« Last Edit: August 24, 2011, 06:50:02 AM by NOTORIOUS VR » Logged

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« Reply #12 on: August 24, 2011, 07:39:17 PM »

Weird. This is what I have in my bins

4Z7907551R 0.09783
8D0907551F 0.06756 (RS4)
8D0907551G 0.09778
8D0907551M 0.14696 !!!

unless I have a non-stock mbox bin floating around.
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« Reply #13 on: August 24, 2011, 08:01:23 PM »


I just discovered the problem. When I did my XDF, I primarily used the a6 R-box as a reference, which uses factor 0.000167 for KRKTE

However, F and G both use .000111

I'm so sorry guys, this is all my fault. My XDF is WRONG!

Here's the deal:

Code:
          Factor   Value   HexValue
4Z7907551R 1.667E-4 0.09783 0x24b
8D0907551F 1.111E-4 0.06756 0x260
8D0907551G 1.111E-4 0.09778 0x370
8D0907551M 1.111E-4 0.09778 0x370

Notice M and G are the same Sad

ETA:

Fix available here (version 20110825)

http://nefariousmotorsports.com/forum/index.php/topic,200.msg8108.html#msg8108
« Last Edit: January 04, 2017, 11:34:03 AM by nyet » Logged

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Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience.
judeisnotobscure
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« Reply #14 on: August 24, 2011, 08:06:45 PM »

ah, now it makes so much more sense.
good catch
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