Batch fire confusion

In the Injector Drives introduction video, it is said of Batch Fire "This is where all the injectors are pulsed together at the same time."

Im still confused on this, I dont understand why they would all simultaneously spray fuel. Or was it meant that the injectors spray in groups? If we're talking about a 4 cylinder engine for example, are they sprayed in groups of two? and if so, what cylinders would be grouped? Thanks

Maybe the statement "this is where all injectors are pulsed together at the same time" is a little ambiguous as they may not always be fired together, but I think the main point is the term "batch fire" in this case is just being used to differentiate between "sequential injection" (where the injection event is timed synchronous to the engine cycle) Vs any other "batch fire" strategy (where the injection events arent timed in phase with the engine cycle).

There are multiple variations of "batch fire" as well as many different terms used by the different ECU manufacturers to describe their strategies. Some fire all together every 360 or every 720deg, some may fire them in 2 or 4 alternating groups, etc. The main thing to understand is none of these batch fire strategies will result in any injector firing at an ideal time for any cylinder.

To answer the second bit of your question about how they should be grouped etc, that will depend on the specific ecu strategies available, the engine/manifold design, injector size, firing angles, trigger system, etc. Is sequential not available?

As Adam said.

With an engine with an equal number of cyinders and where there will be two at the injection point on every revolution.

You will easily identify them by the firing order, for example in-line 4 will batch fire 1&4, and 2&3 as they're paired. In-line 6s and some V6s with a 153624 firing order will batch fire 1&6, 2&5, and 3&4. For a V8 with a 18436572 (old Chev') it'll be 1&6, 8&5, 4&7 (later engines reverse those, but same principle), and 3&2, as those cylinders will move together.

Thing to remember is to approximately HALF the injectors' opening compared to full sequential, where they would only open once every 720 degrees, rather than twice every 720 when batch fired. This sometimes referred to as semi-sequential, as it's a sequential process but doubled/halved.

Same principle is used with batch fired ignition coils, but I don't think they can be used together - might be wrong, though.