Hydrogen Internal Combustion Engines (H₂ICEs) offer the potential for near-zero carbon emissions. However, while nitrogen oxide (NOₓ) emissions have been extensively studied, particle number (PN) emissions, primarily resulting from lubricant oil pyrolysis due to hydrogen’s short quench distance, remain less well understood. This study investigates exhaust particle characteristics from a spark-ignition, single-cylinder research engine, based on MAHLE Powertrain’s downsizing engine combustion system, at Brunel University, London. It compares gasoline and hydrogen direct-injection strategies (central vs. side injection) across a wide range of operating conditions, including variations in engine speed, load, air-fuel ratio (λ), rail pressure, and spark timing.
PN and particle size distribution were measured using Cambustion’s DMS500, paired with a catalytic stripper to isolate solid particles. To assess the impact of engine wear, tests were conducted on both a worn engine configuration (~30% cylinder leakage) and a newly overhauled state (~5% leakage). Additionally, a production Euro 6 Gasoline Particulate Filter (GPF) was evaluated under hydrogen combustion to determine its effectiveness in capturing the small particles typically associated with H₂ICE operation.
Hydrogen combustion produces significantly smaller particles than gasoline and the PN emissions are highly influenced by injection strategy, lambda, rail pressure, and engine wear, particularly due to increased oil ingress in worn engines. Compared to gasoline, hydrogen shifts the PN distribution toward smaller diameters, emphasizing the importance of sub-23 nm regulation and measurement practices. GPFs show potential for effective PN reduction under hydrogen operation, though performance depends on injection mode and calibration, given the dominance of ultrafine particles.
Overall, the study identifies critical operating and design factors that influence PN emissions in hydrogen direct-injection engines. These insights support the development of SPN10/SPN23 compliance strategies and inform filtration system choices for durable, low-emission H₂ICE powertrains.