Most port fuel injection systems are double-fire?

[DGXR]

Watching a youtube video on various fuel injection systems, I see the screenshot below. Is this correct? Most modern port-injection systems pulse twice per cycle? I always thought computer controlled port injection systems were smart enough to inject fuel *only* at the intake stroke.

 

[Jetronic]

It's not good for driveability to fire injectors on intake stroke. More likely they fire after intake stroke to give the fuel a chance to evaporate.

 

[Trav]

There is a reason for this, it is true most are that type (AKA simultaneous injection) of system but there is another type called Saturated (AKA Peak and Hold) that does fire the injectors once per stroke.
Peak and hold units were common in the 80's-90's they can be distinguished from the more common simultaneous ones by their ohms they are low ohm injectors usually 2.2-2.5 ohm, the simultaneous are 12-16 ohm.

Low ohm injectors run much hotter and strain the ecm much more than high ohm injectors, it was not uncommon to find blown injector drivers with those. Oddly enough the DI are also saturated 1.1-1.2 ohm and fire once per stroke but modern electronics have overcome much of the issues.
There have been books written on this and the many types of injection so I will leave it here.

Edit: A couple of articles for those that are interested.

http://faculty.ccbcmd.edu/~smacadof/Books/A8StudentWorkBooks161/SWB_a8_m06_Final.pdf

https://www.hondata.com/tech-low-high-impedance-injectors

 

[DGXR]

There is a reason for this, it is true most are that type (AKA simultaneous injection) of system but there is another type called Saturated (AKA Peak and Hold) that does fire the injectors once per stroke.
Peak and hold units were common in the 80's-90's they can be distinguished from the more common simultaneous ones by their ohms they are low ohm injectors usually 2.2-2.5 ohm, the simultaneous are 12-16 ohm.

Low ohm injectors run much hotter and strain the ecm much more than high ohm injectors, it was not uncommon to find blown injector drivers with those. Oddly enough the DI are also saturated 1.1-1.2 ohm and fire once per stroke but modern electronics have overcome much of the issues.
There have been books written on this and the many types of injection so I will leave it here.

Edit: A couple of articles for those that are interested.

http://faculty.ccbcmd.edu/~smacadof/Books/A8StudentWorkBooks161/SWB_a8_m06_Final.pdf

https://www.hondata.com/tech-low-high-impedance-injectors

Looks like page 13 has the meaty info that answers my question. Thanks for posting the link.