Influence of Crankcase Ventilation on Oil-Derived Emissions in a Hydrogen-Fueled Internal Combustion Engine

Crankcase ventilation has a dual influence over hydrogen accumulation in the crankcase and lubricant-derived emissions in hydrogen-fueled internal-combustion engines (H₂-ICEs), yet the magnitude of that influence is still poorly quantified. The present investigation addresses this gap by systematically varying crankcase ventilation flow rate and testing the influence of blowby routing on the emissions of a 2.3 L turbocharged, direct-injection H₂-ICE equipped with a variable-speed sump pump and two oil separators. The engine was held at four steady-state operating points spanning 2 500–3 500 rpm and 5–10 bar brake mean effective pressure, all under ultra-lean mixtures with global excess-air ratios between 2.6 and 3.2. At each point the crankcase ventilation system outlet mass flow was incremented from 6 to 20 kg/h. Elevating the flow diluted the in-crankcase hydrogen concentration from roughly 25 000 ppm to below 10 000 ppm, reducing the mixture to less than one-quarter of the lower flammability limit, while concurrently increasing CO₂ emissions, with the most pronounced rise occurring at 3 500 rpm. A complementary ventilation flow mass-balance was used to quantify the blow-by mass flow rate to the crankcase. Particle-number (PN) emissions were found to depend far more on gas routing than on absolute flow: eliminating recirculation to the intake manifold reduced tail-pipe PN by 26–35 % regardless of the ventilation rate. Size-resolved aerosol measurements downstream of the oil separators revealed exclusively sub-micron droplets, confirming that conventional oil separators capture coarse oil yet permit fine aerosol transport. Correlating hydrogen dilution with oil-aerosol breakthrough indicates that safety and emission improvements can be reconciled only by pairing a high crankcase ventilation flow with a high-efficiency sub-micron filtration stage. These insights give practical guidance for designing crankcase-management systems in next-generation lean H₂-ICEs.