mk e wrote:
apalrd wrote:
There isn't usually a target for the puddle mass. There is a model of what goes in (X) and what comes out (Tau) and steady-state the two balance so no fuel change is needed.
Do you have this modeled somewhere? can you share the model?
I was speaking to Jim (from enginelab) last night he's trying to build a "plant" or engine simulation to go along with the upcoming generic engine control model.....but this is not a trivial simulation.
Getting back to all of the forums I ignored in the last few months.....
Basically x-tau models fuel puddles with two tuned parameters (X and Tau).
X is the amount of fuel that doesn't evaporate into the airstream, but instead puddles. So, Fuel_Charge = (1-X) * Fuel_Injected. The puddle then accumulates the rest of the fuel, so puddle = puddle + X*Fuel_Injected.
Tau is the time constant of the fuel evaporation. Fuel that evaporates goes into the engine. Fuel_Evaporated = puddle * (tau/dt) where dt is the time between cycles
So puddle = puddle + X*Fuel_Injected - puddle*(tau/dt) and Fuel_Charge = (1-X)*Fuel_Injected+puddle*(tau/dt)
Then you just have to solve backwards for fuel injected from desired fuel charge.
X is only dependent on temperature (usually coolant temp is used because the port area is close to coolant temp). Tau is dependent on only coolant temp and RPM. Neither needs many tunable points. The model I saw (an example engine model for my controller) used a 5-cell X table and a 5x5 Tau surface.
I'm currently working on a stacked x-tau system. The outer loop models the puddle in the runner from the upstream injector and the inner loop models the puddle at the port. From that, I should be able to calculate the downstream fuel quantity precisely, even as the upstream injection split is changed or split injection is turned on/off. I'll let you know how well it works when I test it, it should be running on the dyno in the next two months.