Comprehensive Review of Hydrogen and Tyre Pyrolysis Oil as Sustainable Fuels for HCCI Engines

This review article provides an overview of the use of hydrogen and tyre pyrolysis oil as fuels for homogeneous charge compression ignition (HCCI) engines. It discusses their properties, the ways they are produced and their sustainability, which is of particular importance in the present moment. Both fuels have certain advantages but also throw up many challenges, which complicate their application in HCCI engines. The paper scrutinises engine performance with hydrogen and tyre pyrolysis oil, respectively, and compares the fuels’ emissions, a crucial focus from an environmental perspective. It also surveys related technologies that have recently emerged, their effects and environmental impacts, and the rules and regulations that are starting to become established in these areas. Furthermore, it provides a comparative discussion of various engine performance data in terms of combustion behaviour, emission levels, fuel economy and potential costs or savings in real terms. The analysis reveals significant research gaps, and recommendations are provided as to areas for future study. The paper argues that hydrogen and tyre pyrolysis oil might sometimes be used together or in complementary ways to benefit HCCI engine performance. The importance of life-cycle assessment is noted, acknowledging also the requirements of the circular economy. The major findings are summarised with some comments on future perspectives for the use of sustainable fuels in HCCI engines. This review article provides a helpful reference for researchers working in this area and for policymakers concerned with establishing relevant legal frameworks, as well as for companies in the sustainable transport sector.