Onboard Measurements of Nanoparticles from a SCR-Equipped Marine Diesel Engine

In this study nanoparticle emissions have been characterized onboard a ship with focus on number, size, and volatility. Measurements were conducted on one of the ship’s four main 12 600 kW medium–speed diesel engines which use low sulfur marine residual fuel and have a Selective Catalytic Reduction (SCR) system for NOX abatement. The particles were measured after the SCR with an engine exhaust particle sizer spectrometer (EEPS), giving particle number and mass distributions in the size range of 5.6–560 nm. The thermal characteristics of the particles were analyzed using a volatility tandem DMA system (VTDMA). A dilution ratio of 450–520 was used which is similar to the initial real-world dilution. At a stable engine load of 75% of the maximum rated power, and after dilution and cooling of the exhaust gas, there was a bimodal number size distribution, with a major peak at ∼10 nm and a smaller peak at around 30–40 nm. The mass distribution peaked around 20 nm and at 50–60 nm. The emission factor for particle number, EFPN, for an engine load of 75% in the open-sea was found to be 10.4 ± 1.6 × 10¹⁶ (kg fuel)⁻¹ and about 50% of the particles by number were found to have a nonvolatile core at 250 °C. Additionally, 20 nm particles consist of ∼40% of nonvolatile material by volume (evaporative temperature 250 °C), while the particles with a particle diameter <10 nm evaporate completely at a temperature of 130–150 °C. Emission factors for NOX, CO, and CO₂ for an engine load of 75% in the open-sea were determined to 4.06 ± 0.3 g (kg fuel)⁻¹, 2.15 ± 0.06 g (kg fuel)⁻¹, and 3.23 ± 0.08 kg (kg fuel)⁻¹, respectively. This work contributes to an improved understanding of particle emissions from shipping using modern pollution reduction measures such as SCR and fuel with low sulfur content.