This thesis is the resume of my 6 months engine calibration activity done at DENERG, the department of energy at Politecnico di Torino. Thanks to that I learned to manage an engine test bed with all the instrumentation and help the team into post-processing activity of the data come from the tests. This activity is focused on the study of unconventional combustion PCCI in diesel engine. In particular we use an FPT engine already in production with some hardware modification to sustaine better the PCCI combustion. In the first part of the thesis I explained all the characteristics of diesel engine, the pollutant formation mechanisms and all the aftertreatment devices.