2009 2010 F1 non DI Fuel Systems

[Brian P]

The air at the bellmouth is still moving in at IVC. It hasn't "realized" that the cylinder has stopped drawing air in yet. They stop injection when the "spitback" pulse comes back up the intake runner.

To me, it looks like they are trying to synchronise fuel delivery and air motion the best they can, so that the intake runner already contains a premixed and mostly evaporated (and cooled) charge ready for the next cycle. They're minimizing how much they rely on in cylinder charge motion to do the mixing.

[mk e]

I'm wondering if the rules fixed the max injector size? It might be that simple?

[Brian P]

The rules fixed the max injection pressure (and the use of a single injector per cylinder). It's apparent that they want the smallest possible droplet sizes, and that's consistent with using the highest possible injection pressure. It seems apparent that they want to pre mix the air and fuel as evenly as possible in the intake runner, and that means coordinating the injection period with the air inflow period into the bellmouth. That sets the target duration to be (roughly, but as close as they can get it) the same as the intake duration. Pressure is set (as high as possible), duration is set (about 40% duty cycle at full engine load), that sets the injector flow rate.

[mk e]

That was my thinking too....but with a 40% dc they are still injecting after ivc so that fuel is trapped in the runner until next cycle getting warm and possible ending up in another cylinder. The Honda paper lists a 100L/min static flow rate....which seems an oddly round number and what prompted me to wonder if it was set by regulation because the odds of a nice round number being picked by testing and analysis are about 0 and other stuff I've seen/read suggest a max DC closer to 35% is optimal.