GDI firing angle values, looking for explanation

[Tor]

Is there anyone who can say exactly what these values are? Perhaps someone with Ecutek can tell how they are described?

I assumed it's the end of injection in deg before exhaust stroke TDC. But something doesn't add up in my mind.

I.e. a value of 360 would mean injection ends at TDC on the combustion stroke? Or 370 means it ends 10 deg prior to TDC on the combustion stroke?

But e.g. a value of 300. It would then mean the injection ends 40 after TDC on the combustion stroke. But let's say there is 30 ignition advance at that point. It would still be injecting long after the spark has been fired (70 deg). That can't be, right?



Or is it like this: Fuel injection end (crank angle)? That would make more sense?

[steve99]

Their was a guy on this forum a while back called arghx7

throw in a google search as below you get a lot of his info. I suspect he was automotive engineer


gdi arghx7 site:www.ft86club.com

[Tor]

Originally Posted by steve99

Their was a guy on this forum a while back called arghx7

throw in a google search as below you get a lot of his info. I suspect he was automotive engineer


gdi arghx7 site:www.ft86club.com

Thanks, good idea with the google search, the forum doesn't allow to seach for less than 4 letters, so GDI is difficult.

The info below doesn't shed a clear light on it and I'm not sure if it's correct. Start of injection doesn't seem to make much sense to me, since end of injection would then vary depending on injector pulse width?

I was hoping maybe Ecutek had a clear cut description of the table?

Originally Posted by arghx7

It depends on how exactly the injection timing calculation is performed. Basically, those degrees probably don't represent actual physical crank angle degrees. There is probably an offset, say 40 or 60 degrees. The reason for this is the fact that the calculation is based on synchronization with the cam and crank position sensor from the last cycle. The sync point is, generally speaking, not at true TDC.

So, throwing some numbers out there: at low rpm low load (upper left portion of the map), we see a value of 320 degrees. Let's say there's a 40 degree offset. So in that case, 320 - 40 = 280 degrees BTDC start of injection. Or if the offset is 60 degrees, the SOI would be 260 degrees BTDC. Again, I made that 40 and 60 degree numbers up, but if you put an oscilloscope on the cam and crank sensors you could calculate the offset given enough other information.

At the lower right corner of the map, you have 370 degrees. That means SOI is 50 degrees earlier than at low load, low rpm (320 value). If the offset is 40 degrees, that would mean SOI at high rpm & high load is 370 - 40 = 330 degrees BTDC.

The trend of advancing SOI at higher rpm appears to remain the same, assuming we are calculating this right. It all comes down to the formula used... maybe you need to add or subtract 180 degrees or something to make it work. Whoever wrote the software and originally tuned these maps know. We have to make educated guesses.

[Tokay444]

I would say 300 would be 60* before TDC, not 40* after, and 370 would be 10 degrees after TDC.

[Tor]

Originally Posted by Tokay444

I would say 300 would be 60* before TDC, not 40* after, and 370 would be 10 degrees after TDC.

That would make sense to me as well. So like the other table: Crank shaft angle and presumeably end of injection.

[Tokay444]

Originally Posted by Tor

That would make sense to me as well. So like the other table: Crank shaft angle and presumeably end of injection.

We should be able to log injector duty cycle to find out.

[Tor]

Originally Posted by Tokay444

We should be able to log injector duty cycle to find out.

More brains think better than one...

Random Ecutek log:



- 720 deg crankshaft rotation at 6000 rpm should take 20 ms.
- 5 miliseconds is 180 deg (DI injection end to spark) <- makes no sense, would be on the exhause stroke 360 - 31 - 180 = 149 deg end time
- 4.4 miliseconds is 158 deg (injection time DI)

Assuming the GDI firing angle table at 6000 rpm has a value of 390.

What is 390?

[Tokay444]

I misspoke. I meant injector pulse width. Not duty cycle. We may need an oscilloscope to get exact values, vs what the ECU outputs, but you're right, that log does not seem to add up.

[Tor]

Originally Posted by Tokay444

I misspoke. I meant injector pulse width. Not duty cycle. We may need an oscilloscope to get exact values, vs what the ECU outputs, but you're right, that log does not seem to add up.

Here IPW in one of my own logs. I assumed Ecutek recalculated that into a time (injection time DI final):

https://datazap.me/u/tor/tor-2373-0?...8-809&mark=745

I don't get how you will calculate that into an angle?


The reason for my interest is that if the values in the table are fully understood, it might be more easy to adjust them using logic and other known values.

Refering to another thread I made a few days ago.
http://www.ft86club.com/forums/showp...24&postcount=7
Example 2 was solved with a 20 deg change in the GDI at low rpm. This was luck and undoing some changes. It would be nice to know exactly what I changed and be able to compare it with ignition timing and AVCS to see a logic behind it.

[Kodename47]

The GDI tables are start of injection before TDC at the end of compression/start of expansion phase. 360 would be start of injection at the start of the intake phase.

[Tor]

Originally Posted by Kodename47

The GDI tables are start of injection before TDC at the end of compression/start of expansion phase. 360 would be start of injection at the start of the intake phase.

Thank you!

With the Ecutek log above, of course I made several mistakes.

They should just all be added up:

31 ingnition timing advance
180 end before ignition
158 injection time
=
369

That would of course be a value that makes sense!

Or same log at 2500 rpm (48 ms)
22 ingnition timing advance
265 end before ignition (17.7 ms)
29 injection time (1.9 ms)
=
316
Load in the log is 0.7, seems very plausible!

Originally Posted by Tor

Refering to another thread I made a few days ago.
http://www.ft86club.com/forums/showp...24&postcount=7
Example 2 was solved with a 20 deg change in the GDI at low rpm. This was luck and undoing some changes

With the above in mind, I am questioning if the change of 20 deg at low rpm would matter at all with such short injection times or if it's just coincidence that it's not doing it anymore. That's really just a tiny squirt.

Would it really be realistic to think the injection in either for these two places would make a significant difference?

[freerunner]

Originally Posted by Tor

Would it really be realistic to think the injection in either for these two places would make a significant difference?

Have you advanced or retarded the point of time of the injection with the 20 deg 'fix'?
I could imagine that it could indeed make a difference. In terms of teh right amount of turbulence to swirl and/or more time to get a more homogeneous mixture.

I haven't touched the gdi settings yet, nor tried to understand the defaults. Does it not make sense to inject as soon as possible after or at the overlap/scavenging phase (without pushing the charge out of the exhaust, of course)?
What is your opinion on that?

[Tor]

Originally Posted by freerunner

Have you advanced or retarded the point of time of the injection with the 20 deg 'fix'?
I could imagine that it could indeed make a difference. In terms of teh right amount of turbulence to swirl and/or more time to get a more homogeneous mixture.

I haven't touched the gdi settings yet, nor tried to understand the defaults. Does it not make sense to inject as soon as possible after or at the overlap/scavenging phase (without pushing the charge out of the exhaust, of course)?
What is your opinion on that?

I'm an absolute injector noob which is evident from my previous posts in this thread already. It didn't interest me much before this. So I'm trying to get my head around terms and concepts as I go along, so please don't take any advice from me.

The "20 deg fix":
I restored the injector timing to stock 300. I had previously increased it to 320 as the rest of the "default" values in the table because I thought the cams were totally different from the stock tune in that area.

I just adjusted my cams, see this thread/post. I made 2 different exhaust cams settings at low rpm. With the 320 it runs well on my car with the more aggressive cam. The other car had the problem with the less aggressive cam and 320. But now, I think I'll restore my values too as the exhaust cam should have zero influence at that point of injection as I see it. Probably, it's rather that I don't drive much in 6th gear and just didn't see the problem.

You could well be right it's a matter how it mixes. I think cooling effects can be ruled out, with such short injection - I can't imagine it would matter much if it's 20 deg sooner or later? I can also imagine that it shouldn't be too long from injection to ignition so as for the fuel not to end up on the cylinder walls? I suppose it won't stay suspended in the air forever?

Looking at the cam lobes at higher rpm, it seems they all have "end of injection" where the intake valve starts to close again. Could be a coincidence or it could be on purpose? I didn't check the stock tune yet but the OFT vs. my own cam timing. As far as I recall, it even started to inject in one rpm area before the intake valve had begun to open.

I think I read a long time ago somewhere that there is an advantage to advancing the injection in terms of cooling. It would make sense if a large volume of fuel is injected (and the injection phase is relatively long, and there is still a relatively short time to ignition) that it is in the combustion chamber for the longest time possible, before starting the next combustion?

Edited to add: I also read that injecting with the piston near TDC helps cool the spark plug as the fuel bounces off the piston and hits the plug.

Please take my first paragraph into account again. Just thinking out loud.

HP academy should come out with a webinar on just this topic soon. I hope he will share some wisdom and general concepts and dos and don'ts.

[Kodename47]

From memory you want the DI to inject as late as possible to help with thermal control in the cylinder, but early enough that there is a good mixture. We do have the PI to help with the latter. I've not read that about spark plug cooling, but I would suggest it's the same as.charge/cylinder control. Also inject too early and you get wall wetting and oil dilution issues.

The PI ratio, VE and SOI DI timing are all related. Look at the OEM maps and you can see the link.