The increasingly stringent regulations regarding greenhouse gas and pollutant emissions imposed by the European Union through both the Fit-for-55 package and the Euro 7 standard require the rapid development of innovative and environmentally sustainable propulsion systems. Among the wide range of possible solutions, high-efficiency internal combustion engines and their integration into hybrid powertrain architectures represent a viable pathway, at least in the short term. Within this framework, the Horizon 2020 PHOENICE project was developed with the aim of demonstrating the potential of a plug-in hybrid electric vehicle to reduce both pollutant emissions and fuel consumption. The adoption of innovative technologies, such as highly diluted charge operation, an electrified turbocharging system and an innovative in-cylinder charge motion, enables indicated efficiency values of up to 47%.