Design trends and challenges in hydrogen direct injection (H2DI) internal combustion engines – A review

The hydrogen internal combustion engine (H 2 -ICE) is proposed as a robust and viable solution to decarbonise the heavy-duty on- and off-road, as well as the light-duty automotive, sectors of the transportation markets and is therefore the subject of rapidly growing research interest. With the potential for engine performance improvement by controlling the internal mixture formation and avoiding combustion anomalies, hydrogen direct injection (H 2 DI) is a promising combustion mode. Furthermore, the H 2 -ICE poses an attractive proposition for original equipment manufacturers (OEMs) and their suppliers since the fundamental base engine design, components, and manufacturing processes are largely unchanged. Nevertheless, to deliver the highest thermal efficiency and zero-harm levels of tailpipe emissions, moderate adaptations are needed to the engine control, air path, fuel injection, and ignition systems. Therefore, in this article, critical design features, fuel-air mixing, combustion regimes, and exhaust after-treatment systems (EATS) for H 2 DI engines are carefully assessed. • Key design aspects for achieving high efficiency and low emissions summarised. • Injection and intake ports are critical for good in-cylinder mixture formation. • Thermal management is required to mitigate abnormal combustion. • Advanced boosting system required to obtain high power density.