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Discussion and questions related to the course EFI Tuning Fundamentals
watched the accel enrichment webinar but still not 100% sure on what the wall wetting and fuel film rolls play?
Is there a particular ECU you had in mind?
Wouldn't it be the same regardless of ecu type? I'm more so trying to understand why its used
Some ECUs have a specific wall wetting algorithm (for example "X-Tau" on Megasquirt and Ford applications) based in part on physical model of fuel wetting and evaporating in the intake port. Others just have a sort of look up table to add extra fuel that is not based on a model.
so when fuel is injected into the port some of it evaporates so by wall wetting is that injecting abit more fuel into the port so once that evaporates we will still have the correct amount of fuel for out target afr? am I on the right track ?
Yes exactly. Some ecu's calculate how much fuel evaporates plus how much fuel is sticking to the walls. This is a more advanced way to do acceleration enrichment. If you know the quantity of fuel sticking per cycle and the evaporation rate you can calculate the additional fuel to add with each injection pulse.
That amount depends on the port geometry, the manifold vacuum, and the temperature. In real world it's mostly guess and check tuning.
I'm super late to this part Tony but I just wanted to add that the majority of aftermarket ECUs ignore the wall wetting (what's actually going on inside the engine) and instead put a reasonably effective bandaid on things by scheduling transient fuelling based off rate of change of TPS. On this sort of ECU you don't really need to understand what's going on in the background.