Recent Fuel-Based Advancements of Internal Combustion Engines: Status and Perspectives

This Review provides a critical analysis of the latest research results, future challenges, and opportunities regarding fuel-based achievements for boosting efficiency and reducing emissions of internal combustion engines (ICEs). Electro-fuels (E-fuels), biofuels, natural gas, hydrogen, and ammonia are among recent alternative fuels which are considered fuel-based solutions. Moreover, fuel nanoadditives including carbon nanotubes, cerium oxide, zinc oxide, and metallic nanoparticles are also considered fuel-based solutions from another point of view. Attention is given to the production, types, and specific physical, chemical, and combustion characteristics of alternative fuels and nanoadditives regarding ICEs performance, efficiency, and emissions. E-fuels and biofuels are investigated in terms of their production, features, and effect on ICEs as well as required upgrades regarding combustion systems and strategies to adopt their drop-in. Reaching 90% of hydrogen energy share and minimal carbon emissions, combustion concepts of natural gas/hydrogen/ammonia-fueled ICEs are presented in detail with the challenges, opportunities, and required modifications to leverage these fuels in existing engines. Building on past research results, the enhancement of chemical kinetic models for studying the combustion of hydrogen and ammonia blends in addition to the risks associated with improper hydrogen/ammonia combustion, including preignition, knock, and backfire, are explained under different conditions. Much space is devoted to the effects of nanoadditives on combustion quality, emissions, and engine efficiency since their effects extend to improvement of fuel thermophysical properties and boosting the brake power by ∼8% at a concentration of 90 ppm. Different techniques of water injection are presented as part of fuel-based solutions, where direct water techniques are noticed for the significant reduction of NO_x emission up to 20% without EGR and up to 90% with EGR. It is concluded that the cost of these fuel solutions is still high compared to conventional fuels, however, innovations and continuous research will make them in hand shortly. So, adaptation of ICE systems to be ready for these fuels becomes imperative to enhance the efficiency and reduce the emissions.