Abstract
To achieve the goals of low carbon emission and carbon neutrality, some urgent challenges include the development and utilization of low-carbon or zero-carbon internal combustion engine fuels. Hydrogen, as a clean, efficient, and sustainable fuel, has the potential to meet the abovementioned challenges. Thereby, hydrogen internal combustion engines have been attracting attention because of their zero carbon emissions, high thermal efficiency, high reliability, and low cost. In this paper, the opportunities and challenges faced by hydrogen internal-combustion engines were analyzed. The progress of hydrogen internal-combustion engines on the mixture formation, combustion mode, emission reduction, knock formation mechanism, and knock suppression measures were summarized. Moreover, possible technical measures for hydrogen internal-combustion engines to achieve higher efficiency and lower emissions were suggested.