<p>How can I center a model at the middle of the printing area of the printer when creating a g-code with CuraEngine. </p>

<p>Are there any parameters I can add to <code>ultimaker2.def.json</code> to achieve this?
Thanks.</p>

If this is over the commandline tool "CuraEngine", then you will have to read the sourcecode. According to the
Author
, 'Nope. Only documentation there is in the code, readme and my head.' (cringe!).
If you're talking of the GUI program, then right click and click "Center". But this requires GUI usage. Not so nice if you want to automate using curaengine as your slicer.