Hi,
It is possible that the the step size is unfortunately too large for the model to simulate stably. I recommend using the variable step solver (i.e., no local solver) while developing a model, as it is generally more robust.
If you need to run the model in fixed step, then you will have to decrease the step size and/or increase the number of non-linear iteration. When running in fixed step and the step size is not small enough, it is common to get a failure near the start of simulation. This is because the initial values of the variables in the model are not always close to where they want to be.
Therefore, one way to improve it is to set the initial values of variables (e.g., pressure ,temperature, etc.) closer to where they should be (for example, based on the results obtained from a variable step simulation). You can even consider using the Simscape operating point to save an operating point a few second after the simulation starts (when it looks like things have settled down), and start the simulation from the saved operating point instead.
If the issue still persists, you can try decreasing the initial temperature at either of the pressure chambers and analyze how the model behaves.
I hope it helps.
Regards,
Zuber
