Future of internal combustion engines using sustainable, scalable, and storable E-fuels and biofuels for decarbonizing transport and enabling advanced combustion technologies

Internal combustion (IC) engines have contributed to global economic development in industrialized societies. Hydrocarbon fuels used for fueling the IC engines need to be replaced by sustainable and eco-friendly origins that do not adversely impact the environment locally and globally. Electro-fuels (or E-fuels) and biofuels are essential to displace fossil fuels. They are primarily produced using renewable electricity and feedstocks, respectively, and represent an emerging class of carbon-neutral drop-in fuels for the transport sector, which are becoming increasingly important with every passing day globally and have an essential role in the ‘net-zero’ future. This paper comprehensively reviews the advancements in IC engines to become more efficient in taking the fuel property advantages of various E-fuels and biofuels in existing engines. The paper focuses on several fuels, among the most studied ones in the open literature in the last decade, since their adoption might depend on factors such as the local economic considerations, cultural contexts and the application itself, storability, power requirement, and government policies. The paper covers these fuels by briefly introducing their production pathways and properties. It then focuses on their engine use to meet the future tailpipe and greenhouse gas emissions norms. Challenges regarding the modelling of engines powered by E- or bio-fuels are also included. E-fuels offer a straightforward advantage even in engine-out emissions and after-exhaust emission control technologies. It represents an opportunity to limit GHG emissions. Moreover, the E−(or Bio-) fuels powered engines can cover the same operating range (or a larger one) with similar efficiency or greater than hydrocarbon fuels. However, using these fuels still remain challenging. Retrofitting existing engines for using E−(or Bio-) fuels depends on the cost of the fuel injection system for injecting the fuel into the combustion chamber. The transition from fossil fuels can be done using liquid fuels such as methanol, ethanol, etc., by blending them with conventional fuels. In the long run, methanol, hydrogen, and ammonia are expected to significantly decarbonize the transport sector globally.