Recent progress in the use of hydrogen as a fuel for internal combustion engines

•This paper reviews the recent work on hydrogen-fueled internal combustion engines.•The pros and cons of hydrogen engines are discussed.•Major R&D projects are enlisted, with a discussion of the most important results.•These cover direct injection, heat transfer, modeling and combustion strategies.

Hydrogen-fueled internal combustion engines (H2ICEs) have been the topic of research for many decades, and contemporary reviews have surveyed the relevant literature. Because of a number of relatively large R&D projects that have been ongoing recently, much progress has been made that is worth reporting. Specifically, this paper reviews the advancements made in plotting the possibilities offered by direct injection of hydrogen, in-cylinder heat transfer, modeling and combustion strategies (on an engine as well as vehicle level). These efforts have resulted in impressive efficiency numbers, both at peak and part load operation, while keeping emissions far below regulatory limits and reaching satisfactory specific power outputs. New demonstration vehicles have been put on the road showing the relatively low barriers (on a vehicle level) to introduce hydrogen engined transportation and these are briefly described. The paper discusses the merits of H2ICEs but also what makes them potentially unfit as a realistic alternative. Finally, the paper concludes with the main areas of research that require further efforts.