Investigating the lubricant effect on hydrogen engine particulate emissions – part II: Influence of oil formulation and operating condition

The examination of the morphology and chemical content of lubricating oil-derived particles is essential for understanding the ramifications of our current decarbonisation trajectory, as research on these emissions is notably scarce, particularly in the context of hydrogen as a potential propulsion medium. Consequently, a spark-ignited hydrogen engine was tested under a series of 21 steady state conditions with four different oils (baseline, low & high ash, and high viscosity). The study examines particle elemental composition, morphology, size, count, and influence of oil formulation. A differential mobility spectrometer (DMS500) with a catalytic stripper, transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectroscopy were employed to characterise the particles emitted. The solid particle number (SPN) values for each oil and all 21 conditions were near or below the DMS resolution limit of 1 × 10 4 /cm 3 with a variety of particles ranging from 10 to 50 nm crystalline structures to agglomerates (10-100 nm) and large clusters (100 nm-4 μm). Across all oil types, many 10–100 nm and >100 nm s particles were found to be rich in Fe, Ni, Mn, Cr, Al (engine wear), C, Mg, Zn, P, S, Ca (oil additives), and K, Na, F, Cl (coolant residues). Large calcium-rich clusters appear in the high-ash oil, while carbon- and sulphur-rich clusters are found in the high-viscosity oil. • Low solid particle number concentrations found in hydrogen engine exhaust samples. • Four oils were tested resulting in concentrations in the 1 × 10 3 – 1 × 10 5 /cm 3 range. • Measurements challenged the resolution limit of the instrument (1 × 10 4 – 1 × 10 5 /cm 3 ). • The high ash oil was the only case with high particle count at 2 conditions. • No clear winner was identified among the oils relatively to the particle count.