Hydrogen Crankcase Slip Phenomena: Experimental Study of Forced Ventilation Effects on Hydrogen Engine Performance and Emissions

Hydrogen internal combustion engines (H₂ ICE) are showing impressive potential to replace fossil fuel–based ICE platforms with zero-carbon engine-out emissions. However, adopting 100% hydrogen has its challenges due to its unique properties, such as the rapid flame velocity, the minimum igniting energy, and the lowest density. These unique properties of hydrogen impose an increased risk of ignition and combustion of hydrogen in the engine system due to leakage or inadequate ventilation. One of such scenarios is the hydrogen gas in the crankcase as a result of hydrogen slip through the piston rings. In this study, an experimental investigation was conducted on a single-cylinder hydrogen direct injection spark ignition engine, which was originally designed for boosted DI gasoline engine operation. A crankcase-forced ventilation system was designed and adopted with a hydrogen sensor in the closed feedback loop. The hydrogen concentrations in the exhaust gases and crankcase were measured simultaneously by two V&F hydrogen analyzers to assess the total hydrogen slip phenomenon. In particular, the impact of the intake boost and forced ventilation system on hydrogen slip and engine performance was investigated by varying the relative air-to-fuel ratio (lambda) and forced crankcase flow rate, respectively. The study reveals that the hydrogen slip was significantly increased by adopting lean-burn combustion at high-load operations. The results show that the hydrogen slip in the crankcase can be as high as 100,000 ppm with only the natural crankcase ventilation. Forced crankcase ventilation has been shown to be an effective method to avoid hydrogen accumulation in the crankcase and to drop the hydrogen slip in the crankcase by more than 86%. Additionally, the indicated thermal efficiency can be increased by 1.24% by fully recovering the hydrogen into the intake system through the forced ventilation system.