Injector deadtime 2d/3d table reference base/actual/differential

[DerekAE86]

I've got some xspurt injectors coming for my setup and asked them for the deadtime info, etc

They provide actually provide really good info, specific for each ECU brand so you can just copy and paste the data directly into your tables.

But interestingly they provide two deadtime tables; 2d and 3d.

For the 2d table they reference it off the "base fuel pressure" (300kPa), but the 3d they use "differential pressure".

My setup is non-turbo and uses a MAP referenced FPR with a (gauge) pressure sensor and return style system. So the "differential" parameter in the ECU is just fuel (gauge) pressure minus manifold pressure in this case right?

Should I use the 2d table referenced to base fuel pressure, or the 3d table referenced to differential, or 3d table referenced to the actual fuel (gauge) pressure?

I asked their support email - but the guy wasn't actually sure.
 

[essb00]

Use the 3D table referenced to differential fuel pressure - if you have a fuel pressure sensor and you have selected 'fuel system type' = FP sensor.

[koracing]

I agree if they provide the 3D data to use the 3D table (and test to verify of course).  If you don't have a fuel pressure sensor even, the 3D table has the 2D table data in it between the 280 and 320 rows so it would work the same as the 2D if you entered a reference pressure of 300.

If that have that data - do they also have flow data for different ethanol content levels?

 

[DerekAE86]

7 hours ago, koracing said:

do they also have flow data for different ethanol content levels?

They don't provide it - and I asked about Ethanol flow data vs ULP but haven't gotten a response yet.
 

7 hours ago, koracing said:

the 3D table has the 2D table data in it between the 280 and 320 rows so it would work the same as the 2D if you entered a reference pressure of 300.

This was my cause for confusion because the "300" values were the same between the 2D and 3D tables.

But the 2D is using 300 "Base" and the 3D is using 300 "Differential".
So why are the deadtimes the same for "300" when referenced to two different fuel pressure values?

[koracing]

300kpa pressure drop across the injector is going to be 300kpa drop across the injector regardless.  If your fuel system is MAP Referenced - then theoretically you will always have 300kpa pressure drop or differential if that is where you set your base pressure.  Reality, on the other hand, is that fuel pressure does not always stay at the same differential.  For small changes it's probably fine to continue to use just the basic 300kpa value set, while it would be more accurate to have the 3D data  for times when fuel pressure did not maintain the same differential or base pressure.  If you were to set a static fuel pressure system (like GM seems to like, and some Miata's from the factory set to 4bar or 60psi in some cases), your fuel pressure is static, but MAP is still not static, so you would in this case absolutely need the 3D table to characterize the dead time properly as differential pressure will continually be changing depending on the vacuum or boost generated in the intake manifold.

[DerekAE86]

Ah so it's more important to think about the pressure across the injector; pressure of the liquid in comparison to air pressure (or vacuum) inside the manifold?

[Adamw]

The force required to move the pintle is relative to the pressure differential across its seat - i.e. how much pressure is pushing it closed vs pressure pushing it open.  You have rail pressure on the top, manifold pressure on the bottom.  This is typically called differential pressure or relative pressure, Diff FP = FP - MGP.  Since MGP = 0 when the engine isnt running, "base pressure" or "static pressure" is the same as differential pressure when the engine isnt running.  Coincidentally, the pressure differential across the injector is also important to calculate PW from mass flow, so monitoring it improves the accuracy of both deadtimes and the fuel calculation.