It is possible to specify the generator fuel curve with a quadratic function to provide a better fit to real data. We haven't included the option in the regular generator menu to keep things simple for the majority of users. To access the nonlinear fuel curve option:
1) Go to the library view, and open the generator list in the left sidebar.
2) Select an existing generator and click "copy" to create a new generator model to edit.
3) Select this new generator and scroll down the list in the right side pane. Go to the section "Nonlinear Fuel Curve" and check the box for "Use nonlinear fuel curve".
4) You can enter values here, or you can go back to the generator menu in the design view, and the new options for a quadratic function will appear in the "Fuel" tab.

You will need to do your own curve fit with an external software to calculate the three coefficients.