This master thesis is focused on the combustion diagnostics of a dual-fuel diesel/hydrogen engine. A four-zone diagnostic heat release model has been developed for a dual fuel engine application. Successively the model has been used to analyse experimental data from the testing of the dual fuel engine on which the project is based, carried out at Dumarey, and the results have been compared with 3D CFD analysis of the same datasets. The algorithm is able to evaluate the in-cylinder charge chemical and thermodynamic properties evolution during the combustion cycle with minimal computational effort. Furthermore, pollutant emissions are estimated, specifically concerning NOx and particulate matter.