automan001
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« Reply #15 on: September 26, 2016, 12:26:36 PM »
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I'm a bit confused. If it were there to compensate for flame speed, DZWOLA would be advance, not retard, no?
That's what it looks like in 1.8T: DZWOLA Lambda-Abhängigkeit des optimalen Zündwinkels bezogen auf Lambda 1 (10x1) (Basis-Lambda)/grad KW - 0.6484 0.7031 0.7500 0.7969 0.8516 0.8984 0.9531 1.0000 1.0469 1.1016 - 0 0.750 -0.750 -1.500 -2.250 -3.000 -3.000 -1.500 0.000 2.250 4.500 |
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nyet
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« Reply #16 on: September 26, 2016, 12:32:33 PM »
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No. See the subsequent followup posts re: e85 flame speed vs gasoline flame speed.
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automan001
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« Reply #17 on: September 26, 2016, 01:15:18 PM »
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No. See the subsequent followup posts re: e85 flame speed vs gasoline flame speed.
I think we look on the same thing from different points of view. At the graph of flame speed the lambda 0.85 has highest flame speed. At the graph of DZWOLA this is the lowest point (retard -3) to compensate the fast flame speed. If the mixture goes richer, the flame speed drops. That's why retard is lowered and then at lambda 0.65 it goes to advance (+0.75 @ lambda 0.65) because this is lowest flame speed at richest mixture. If you look at the right side of the graph you will see that retard is also decreased and then flips out to advance as AFR goes leaner (+4.75 @ lambda 1.1). The graph of DZWOLA is exactly inverse of the flame speed graph. |
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« Last Edit: September 26, 2016, 01:18:16 PM by automan001 »
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nyet
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« Reply #18 on: September 26, 2016, 01:16:34 PM »
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Yes, I see what you are saying now!
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nubcake
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« Reply #19 on: September 26, 2016, 01:44:27 PM »
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I'm still not convinced by the curve shape in that single picture. All sources I've seen so far suggest that flame front speed increases from ~0.6 to 1.0 in almost a linear way. Check this paper for example. On the other hand, "combustion efficiency" seems to go in line with the DZWOLA shape (page 82 in this book). Either way, I'm not an expert on this subject ( yet?  ), so if I'm wrong, please correct me. I think I'll try zeroing DZWOLA and adjusting KFZW/2 accordingly. It's zeroed in most 2.7 files by the way. |
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automan001
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« Reply #20 on: September 27, 2016, 05:16:57 AM »
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I think I'll try zeroing DZWOLA and adjusting KFZW/2 accordingly. It's zeroed in most 2.7 files by the way.
There is a better solution. Try to shift the entire map to +3 (or whatever retard you have at lambda 0.85) degrees and zero out only left side of the DZWOLA (values that are less lambda 0.85). Adjust ignition angle in KFZW accordingly. In this way you make lambda 0.85 your new zero "tuner's" point. Probably it's better to change this point to 0.82 because they say that the highest flame speed has been found by research to occur at a lambda of about 0.82. In result at WOT you will have 0 intervention of this table, while at leaner mixtures you will observe some advance of ignition angle, especially when it's leaner than lambda 1.0 which will have positive effect on efficiency & fuel economy. |
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« Last Edit: September 27, 2016, 05:18:59 AM by automan001 »
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nubcake
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« Reply #21 on: September 27, 2016, 05:40:01 AM »
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I'm currently tuning the NBO car, so "leaner than 1" should not be possible either way. Besides, I still have my doubts about 0.82 burning faster, than 1. I completely see your point if we assume that burning speeds correlate with that picture, but in this case I'd prefer to experiment myself.  |
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automan001
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« Reply #22 on: September 27, 2016, 09:17:22 AM »
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This should be of concern if running for example E85. Flamespeed drops as mixture get richer.. If Lambda = around 1.00 there is no ign correction. But my question how would DZWOLA look like if running E85. The picture below show that E85 reach 30cm/s around lambda: 0.85
I think in this picture we see fuel-air ratio (not air-fuel ratio). Text under the picture also hints about that. Which means it's is not quite lambda value. Higher value represents more reach mixture. To get lambda we should transpose the value (divide 1 by that value): AFR(lambda) = 1/FAR where FAR is value from that picture. For example 1/1.1764 (fuel air) = 0.85 (lambda air fuel) |
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« Last Edit: September 27, 2016, 09:24:33 AM by automan001 »
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automan001
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« Reply #23 on: September 27, 2016, 09:18:13 AM »
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If we recalculate the F.A.R to A.F.R we should see a graph like this: Found this: Burn speed is greatly influenced by mixture density. If you have more fuel in the mixture, the fuel molecules are closer together and the flamefront will progress more quickly across the chamber.  Verzonden vanaf mijn iPhone met Tapatalk In some pictures we see F.A.R and in some A.F.R, that's probably why it looks so confusing. |
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« Last Edit: September 27, 2016, 09:40:23 AM by automan001 »
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nubcake
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« Reply #24 on: September 27, 2016, 10:08:13 AM »
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That's a good point. The "phi" symbol indeed is supposed to represent the FAR. Now it makes sense. EDIT: However, more food for thought:  |
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« Last Edit: September 27, 2016, 10:34:11 AM by nubcake »
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turbojohan
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« Reply #25 on: September 27, 2016, 11:20:37 AM »
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Calibration engineers don't make this map the way it is if it is Not realistic. So i was searching For a picture That fits the map ;-)
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