The objective of this thesis is an emissive comparison between two different same-rated heavy-duty engines fuelled with different energy sources. The engines are both Cursor-9, one CI and the other SI. The energy sources used are Diesel (taken as reference), CNG and a Diesel-like paraffinic fuel commercially named HVO. All the tests have been carried out in the FPT Industrial testing facility. They are a set of engine bench tests and a set of In-Service-Conformity and PEMS tests. After the introduction to the regulatory environment and the description of the data set, some information taken from papers are reported as starting point.