Nowadays the reduction of the transportation noxious emissions plays a crucial role in the development of new traction systems and new vehicles. All the OEMs are switching from pure thermal powertrains to hybrid or pure electric ones in order to comply with the always more stringent regulations developed with the purpose of emissions reduction. While for passenger cars the industry is moving towards electric powertrains, for heavy duty vehicles the electrification has more limitations given by the energy storage, the increment of the vehicle weight and the recharging time and infrastructure. For these reasons, the hydrogen engine represents a promising technology to achieve immediate improvements in terms of the decarbonization of the transportation sector especially in the heavy duty field.