[pulplus]

Hi to everybody!

I'm simulating hydrogen injection during the compression stroke insinde an internal combustion engine chamber.
The injector is just a simple cylinder with constant area. At its inlet I'm imposing a mass flow inlet condition because I have the experimental data of it. The profile is trapezoidal: a ramp-up from 0 to the target mass flow in 1 crank angle, then a constant mass flow for 15 crank angles and after a ramp down of 1 crank angle.

I'm sure the hydrogen flow is choked throughout the injection. In the mass flow inlet window, I tried to impose only the mass flow profile, but after a few time-steps during the ramp-up the simulation diverged (fluent adviced me that the it was limiting the inlet mach number to 0.98). For this reason, under the hypothesis of choked flow, I have tried to give in the mass flow inlet window also the static pressure profile corresponding to mach = 1. It worked for the ramp-up and the steady state, but anyway the static pressure during the ramp up wasn't the one I assigned in the static pressure profile.
Now I'm having troubles with the ramp-down, fluent does some time-steps correctly, then it starts diverging (also setting a static pressure profile corresponding to the choked condition) and from what I have seen, it calculates a completly non-sense total pressure when it starts diverging. Any suggestions to solve this issue?