Last few days I was thinking about something.
Tailpipes of all 1.8/2.0TFSI I was near stays sootish black, no matter how often I clean them. No matter if they are with stock injectors or slightly bigger ones.
Tailpipes stays dirty and can't be kept clean like the tailpipe of 3.0TDI or 1.4TFSI A3 I used to have.

I was wondering why on some direct injection engine they are relatively clean, and on others they are blackish.
I think the main reason is Start Of Injection (SOI) and balance between time for mixing/evaporation of fuel in cylinder Vs wetting of piston crown/cylinder walls. With bigger injectors it gets even worse because they inject small quantities for part throttles faster (earlier related to how much cylinder is filled with air).

So I start to dig for information of importance of start of injection in direct injection engines.
Here is a good read I found directly related to soot formation.
https://www.researchgate.net/publication/267576831_Particulate_Matter_Emission_Comparison_of_Spark_Ignition_Direct_Injection_SIDI_and_Port_Fuel_Injection_PFI_Operation_of_a_Boosted_Gasoline_Engine

Attached are two citations for above article, that mostly affect my quest for clean tailpipes

It was interesting for me how much reduction there is in the first 10° (between 310 and 300 SOI) and diminishing results after that, even getting worse after 280°.

So now when we have some clue it is time to find a way to correct this.

I'd like to gather all possible threads for SOI of FSI engines together with some basic principles of DI engines in this thread.

So here is one thread I found with good info and some analogy with port injection ME7.
http://nefariousmotorsports.com/forum/index.php?topic=14115.0

Later I'll look at differences between 1.4 and 2.0 KFWBH01SLE maps, if I can find some clue why 1.4 keeps exhaust cleaner than EA888.

Sure it is not only SOI.
However every gasoline engine from VAG after ME7 is aiming for longest possible time at lambda=1.
So both 1.4TFSI and 2.0TFSI try to stay at 14.7:1 AFR almost all the time.

So here it is comparison of 2.0TFSI (upper one) and 1.4TFSI (lower one) KFWBHO1SLE.

2.0TFSI map looks contra intuitive for me with sooner injection for low loads (early in intake stroke), and retarding injection for high loads.
1.4TFSI looks more like I was expecting.

I was thinking about difference of IVO event of both engines, but there is far more similarities in strategy there, compared to SOI strategy.

So next tables are 2.0TFSI (upper both) and 1.4TFSI (lower one) versions of KNWSE. For 2.0TFSI, there is two versions because of AVS system. So roughly until 3000rpm it uses the first one, after that it switches to large exhaust lobes, and starts to use second one.

Definitely first attempt that I'll made will be to retard injection in lower load cruising cells on my current toy. It is with 8V S3 Bosch injectors - roughly 13.5% larger than standard ones - so maybe there is even greater reason to retard injection of small quantities.

Someone could share some info about SOI in Simos18 cars?

For EA888.3 it looks more natural with this SOI map.

Last night I was thinking - maybe it is best to inject fuel when we have greatest velocity of air charge entering the cylinder. Of course we have some constraints - is there enough time to evaporate fuel, is there enough time to inject requested quantity and s.o.
But when velocity of air charge will be greatest? Maybe a moment after piston velocity peaks on the path downward of intake stroke.

Here you can find good information about piston motion.
http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

On the picture below you can see piston velocity and acceleration depending of crankshaft position for w Rod/Stroke R/S = 1.525, which is very close to R/S ratio of 2.0 VAG engines (1.552).

In the table you can find info how different R/S ratio affects few parameters like velocity, acceleration, side load etc.
Still above article is a good read if someone want to understand some basics in a easy way.

Ok! It seems 1.4TFSI SOI map quite well match with my thinking for injecting small quantities on cruising speeds when velocity is greatest and I should try this approach soon.
Maybe the worse think that could happen is to have no effect with such delay of injection for additional 50°.