Nowadays hydrogen, especially if derived from biomass or produced by renewable power, is rising as a key energy solution to shift the mobility of the future toward a low-emission scenario. It is well known that hydrogen can be used with both internal combustion engines (ICEs) and fuel cells (FCs); however, hydrogen-fuelled ICE represents a robust and cost-efficient option to be quickly implemented under the current production infrastructure. In this framework, this article focuses on the conversion of a state-of-the-art 3.0L diesel engine in a hydrogen-fuelled Spark Ignition (SI) one. To preliminarily evaluate the potential of the converted ICE, a proper simulation methodology was defined combining zero-, one-, and three-dimensional (0D/1D/3D) Computational Fluid Dynamics (CFD) approaches. First of all, a detailed kinetic scheme was selected for both hydrogen combustion and Nitrogen Oxides (NOx) emission predictions in a 3D-CFD environment. Afterward, to bring the analysis to a system-level approach, a 1D-CFD predictive combustion model was firstly optimized by implementing a specific laminar flame speed correlation and, secondly, calibrated against the 3D-CFD combustion results. The combustion model was then integrated into a complete engine model to assess the potential benefit derived from the wide range of flammability and the high flame speed of hydrogen on a complete engine map, considering NOx formation and knock avoidance as priority parameters to control. Without a specific modification of turbocharger and combustion systems, a power density of 34 kW/L and a maximum brake thermal efficiency (BTE) of about 42% were achieved, thus paving the way for further hardware optimization (e.g., compression ratio reduction, turbocharger optimization, direct injection [DI]) to fully exploit the advantages enabled by hydrogen combustion
