Climate change concerns demand a drastic reduction in CO2 emissions, tending to what is called carbon neutrality. Even if political guidelines promote electrification, considering the transportation sector, not all applications have the same requirements and boundary conditions, and hence, their optimal solution is not necessarily the same. In this context, in parallel with pure electric powertrains, the internal combustion engine (ICE) still has a relevant role to play, mainly in hybrid powertrains, working together with an electrical motor. In this hybridization context, the spark-ignition (SI) engine used to be the most adopted solution because of its lower cost and complexity. Consequently, it can be concluded that the SI engine still has a significant role to play in the near future. However, when ICEs are considered, the search for carbon neutrality requires the use of fuels other than fossil fuels. At this point, many alternatives arise, from biofuels to synthetic e-fuels, or