This paper provides a comprehensive review and critical analysis of the latest research results in addition to an overview of the future challenges and opportunities regarding the use of hydrogen to power internal combustion engines (ICEs). The experiences and opinions of various international research centers on the technical possibilities of using hydrogen as a fuel in ICE are summarized. The advantages and disadvantages of the use of hydrogen as a solution are described. Attention is drawn to the specific physical, chemical, and operational properties of hydrogen for ICEs. A critical review of hydrogen combustion concepts is provided, drawing on previous research results and experiences described in a number of research papers. Much space is devoted to discussing the challenges and opportunities associated with port and direct hydrogen injection technology. A comparison of different fuel injection and ignition strategies and the benefits of using the synergies of selected solutions are presented. Pointing to the previous experiences of various research centers, the hazards related to incorrect hydrogen combustion, such as early pre-ignition, late pre-ignition, knocking combustion, and backfire, are described. Attention is focused on the fundamental importance of air ratio optimization from the point of view of combustion quality, NOx emissions, engine efficiency, and performance. Exhaust gas scrubbing to meet future emission regulations for hydrogen powered internal combustion engines is another issue that is considered. The article also discusses the modifications required to adapt existing engines to run on hydrogen. Referring to still-unsolved problems, the reliability challenges faced by fuel injection systems, in particular, are presented. An analysis of more than 150 articles shows that hydrogen is a suitable alternative fuel for spark-ignition engines. It will significantly improve their performance and greatly reduce emissions to a fraction of their current level. However, its use also has some drawbacks, the most significant of which are its high NOx emissions and low power output, and problems in terms of the durability and reliability of hydrogen-fueled engines.

Rapeseed vegetable oil was initially zeoformed in the temperature range of 200°Cto 300°C and at a pressure of 1.7 MPa using catalyst containing ZSM-5, and the obtained zeoformates were subsequently converted into hydrocarbons (HVO: hydrorefined vegetable oil) through the process of hydroconversion. The resulting hydroraffinates (HVO fuel biocomponents) contained: n-paraffins, iso-paraffins and up to 15 % of aromatic compounds. It has been established that hydroraffinates containing aromatic compounds have good lowtemperature properties (cold filter plugging point (CFPP) of approximately -12°C) and a density of 825 kg/m 3 . The hydroraffinate obtained over the catalyst at the highest applied temperature (300°C) was characterised by a decreased initial boiling point of distillation (IBP) of 174°C (the IBP for the non-zeoformed oil hydroraffinate was 284°C) and an increased distillation final boiling point (the FBP) of approximately 379°C, which was higher than that of the nonhydroraffinate (337°C). Investigation of the obtained hydroraffinate properties led to the conclusion that the preliminary zeoforming process may cause the coupling (oligomerisation) of fatty acid chains and the creation of aromatic structures containing aliphatic functional groups.

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