Hydrogen fuel offers promising decarbonization pathways for hard-to-electrify transport sectors such as long-haul trucking, international maritime, and aviation. The internal combustion engine (ICE) is and will continue to be important in the transition to net zero emissions (NZE), especially in the transport sector. In this review, the research trend, hotspots, and evolutionary nuances of hydrogen-fuelled ICEs have been investigated. Our analysis reveals that while earlier research primarily focused on the performance and emission characteristics of hydrogen-fuelled ICEs, recent studies are increasingly paying more attention to combustion and emission control strategies. NO_x emissions have received a lot of attention, as it is the most important pollutant from hydrogen engines. Several techniques, namely exhaust gas recirculation (EGR), water injection, and lean combustion, have been predominantly adopted and studied for controlling NO_x emissions. Another major research area in the field has centered on combustion anomalies such as backfiring and knocking, which are key setbacks to the hydrogen-fuelled ICE. Owing to its ability to produce fewer emissions and greater performance than diesel-only operation, hydrogen in diesel engines as dual fuel has also become a major research hotspot in the field within the last decade. Our analysis also showed that there is a strong interest in this field where researchers are focusing on the use of hydrogen with other alternative fuels such as methane, biogas, biodiesel, ammonia, and methanol for optimal operation of the ICE. Finally, we provide some critical challenges and potential solutions related to the use of hydrogen as an ICE fuel. It is anticipated that the results from the present work will pave the way for the continuous development of hydrogen engine research for the ongoing fight to decarbonize the transport sector.

The first part of the current review highlights the evolutionary nuances and research hotspots in the field of nanoparticles in low carbon fuels. Our findings reveal that contribution to the field is largely driven by researchers from Asia, mainly India. Of the three biofuels under review, biodiesel seems to be well studied and developed, whereas studies regarding vegetable oils and alcohols remain relatively scarce. The second part also reviews the application of nanoparticles in biodiesel/vegetable oil/alcohol-based fuels holistically, emphasizing fuel properties and engine characteristics. The current review reveals that the overall characteristics of the low carbon fuel–diesel blends improve under the influence of nanoparticles during combustion in diesel engines. The most important aspect of nanoparticles is that they act as an oxygen buffer that provides additional oxygen molecules in the combustion chamber, promoting complete combustion and lowering unburnt emissions. Moreover, the nanoparticles used for these purposes exhibit excellent catalytic behaviour as a result of their high surface area-to-volume ratio—this leads to a reduction in exhaust pollutants and ensures an efficient and complete combustion. Beyond energy-based indicators, the exergy, economic, environmental, and sustainability aspects of the blends in diesel engines are discussed. It is observed that the performance of the diesel engine fuelled with low carbon fuels according to the second law of efficiency improves under the influence of the nano-additives. Our final part shows that despite the benefits of nanoparticles, humans and animals are under serious threats from the highly toxic nature of nanoparticles.