Hydrogen Internal Combustion Engine Component Investigation and Development for Heavy Duty Truck Applications

Limiting global warming was defined as an essential target at the Paris climate conference in 2015. This target can only be achieved by holistically reducing CO₂ emissions, ignoring sector borders of our industries and broader economy. A significant share of CO₂ emissions in the transportation sector are emitted by Heavy Commercial Vehicles (HCV) due to the required long range and/or high-power requirements. Therefore, HCV’s such as long-haul trucks (LH) are a major focus and for these applications, the hydrogen combustion engine (H₂-engine) offers a promising complement to battery electric and fuel cell electric vehicles, to achieve a CO₂-free commercial vehicle sector.

To achieve the high standards of robustness, safety and function of the conventional diesel engine, extensive investigations must be carried out on the H₂-engine. To enable this, a conventional diesel HD engine was converted to hydrogen and commissioned on a test bench. This publication focuses on the challenges hydrogen combustion presents for the development of the H₂-dedicated components and what is needed to address these. Furthermore, the thermodynamics investigation of the engine in PFI (Port Fuel Injection) and DI (Direct Injection) operation is presented along with the learnings for further component optimizations.

Starting at the system level, lubrication, oil consumption and blowby are conflicting objectives and a central challenge in the development of H₂-engines. The holistic system approach will consider the system comprising of piston, piston rings and liner (PCU) together with the crankcase ventilation system to ensure these conflicting requirements are satisfied. Additionally, this ensures subcritical hydrogen concentrations in the crankcase by scavenging the crankcase with ambient air.

Next with a deeper focus on components, the spark-ignited H₂-combustion process offers the possibility of using aluminum pistons, however the resulting challenges for the piston geometry must be matched against the background of thermomechanical strength.

Additionally, material solutions known from gaseous fuels, which can handle dry tribological conditions, are a good baseline for valves, valve seats and valve guides. Where hydrogen combustion deviates from this experience is with the high potential corrosion load due to the high-water content in the exhaust gas and moderate thermal load. These demands must be considered during the material selection.

After integrating the H₂ specific components the development engine achieved 20.5 bar BMEP and 315 kW peak power, corresponding to > 80% of the baseline engine power. Furthermore, the engine achieved a thermal efficiency, similar to that of the baseline diesel engine, of > 44% in significant areas of the performance map.

The H₂ development engine with its hydrogen specific components presented in this publication is a representative basis for future MAHLE H₂-engine component development and will help to raise the power and robustness of H₂-engines to diesel like levels.