Non-zero emissions from zero-carbon fuel: Emission characteristics of major pollutants and physicochemical properties of soot particles from a PFI heavy-duty hydrogen internal combustion engine.

Hydrogen internal combustion engines (H2ICE) could support low carbon transport, but their particulate emissions require further characterisation. We measured gaseous and particulate emissions from a heavy-duty H2ICE over the WHSC and compared hydrogen engine soot (HES) with diesel engine soot (DES). CO and total hydrocarbon emissions remained low. The particle size distribution was bimodal: the 10 nm peak (1.21 ×106 #/cm3) was 48.6% higher than the 128 nm peak (8.14 ×105 #/cm3). Both soot types comprised aggregates of near spherical primary particles, although HES showed more local clustering and bridging. HES had smaller crystallite spacing, lower tortuosity, and lower ID1/IG, G band FWHM and R3, indicating greater structural ordering. Its sp3/sp2 was 0.46 versus 0.52 for DES, while surface oxygen functional groups accounted for 15.41% versus 25.40%. HES also exhibited higher ignition temperature, temperature of maximum mass loss rate and burnout temperature, together with a higher apparent activation energy, indicating lower oxidation reactivity. The findings provide an integrated experimental comparison of HES and DES under the tested WHSC conditions and may support future investigations of HES formation and aftertreatment applicability.