Even I went to Settings->Config kile->Tools->Build and changed the QuickBuild tool to "LuaLatex+ViewPDF". Every time I save the file, it just keeps running pdflatex. It is not unusable but it is pretty annoying since my doc is pretty big and it is not compatible with pdflatex. My kile version is 2.9.91 and I am running Ubuntu 18.04. Thanks ahead!