Understanding the Hydrogen crankcase Slip Phenomenon and Its Influence on Hydrogen Combustion Efficiency

Hydrogen Internal Combustion Engines (H2ICE) are showing an impressive potential to adopt the existing fossil fuel-based ICE platforms with nearly zero-carbon engine-out emissions. While adopting 100% hydrogen has its challenges, due to the unique properties of the hydrogen such as the rapid flam velocity, the minimum igniting energy, and the lowest density, which could rise safety concerns.

To address one of the major issues, i.e. the hydrogen slip phenomena, an experimental investigation has been conducted by adopting 100% hydrogen direct injection (DI) on a highly downsized spark ignition (SI) engine that was designed and developed for operating on gasoline. A crankcase-forced ventilation system was adopted with a hydrogen sensor in the closed feedback loop. The study was completed by measuring the hydrogen slip from the exhaust and crankcase to fully assess the total hydrogen slip phenomenon. In particular, the impact of the intake boost and forced ventilation system on hydrogen slip and engine performance were investigated by varying equivalent air-to-fuel ratio (AFR) and forced crankcase flowrate, respectively. The study reveals that the hydrogen slip was significantly increased by adopting lean burn combustion though the thermal efficiency can be improved. The results show that the hydrogen slip in the crankcase can be as high as 33000 ppm at lean conditions. Forced crankcase ventilation has shown to be an effective method to avoid hydrogen accumulation in the crankcase. In particular, the indicated thermal efficiency (ITE) can be increased by 3.8% to 44.6% by fully regulating the hydrogen into the intake system.