Engine emissions regulations are becoming increasingly stringent due to the higher concern and visible changes in global warming and people health. Thus, new studies and new technologies are becoming more and more relevant as there is a need to respect these important rules to preserve the safety of people and the world. In this perspective, alternative fuels are useful to decrease the content of net carbon dioxide and pollutants emitted in the environment by exploiting their composition and production. Engines powered by natural gas represent an important step towards the net-zero greenhouse gas emissions EU targets. Natural gas guarantees lower CO2 emissions per units of energy compared to conventional diesel and gasoline engines; it has a higher octane number which allows for higher compression ratios, hence it has a higher thermal efficiency compared to gasoline engines.