Atmospheric Aerosols
Fuel-Dependent Particulate Properties and Soot Structures in Marine Engine Emissions under Biodiesel and Conventional Diesel Operation
Anand Kumar
Zarei, Atefeh[1]; Sapkota, Nishan[1]; Varcoe, Cameron[1]; Guan, Mang[1]; Smith, Brett[2]; Corbin, Joel C.[2]; Sipkens, Timothy[2]; Rochussen, Jeremy[1]; Kirchen, Patrick[1]; Rogak, Steven[1]
Department of Mechanical Engineering, University of British Columbia, Vancouver BC, Canada
Biodiesel is increasingly considered an alternative fuel for heavy-duty marine engines due to its potential to reduce life-cycle carbon dioxide emissions. However, changes in fuel composition can influence particulate matter (PM) emissions and the structure and properties of emitted particles. We assessed PM emissions from a marine diesel engine (2019-built, medium-speed, 4-stroke, rated power output 1920 kW) operating on neat biodiesel (B100, soy methyl ester) and a conventional diesel blend (B5, 95% diesel + 5% biodiesel) over a range of engine loads.
For all operating conditions and fuels, the emitted PM consisted primarily of a mixture of semi-volatile organic material and black carbon (BC), in varying ratios. Transmission electron microscopy revealed that soot particles were predominantly present as collapsed aggregates rather than open, chain-like structures. Such morphology was observed across fuels and loads, although sample dilution and cooling may influence aggregate structure through condensable organic coating, limiting broader generalization. Distinguishing between open and collapsed aggregates is relevant because they differ in particle effective density, aerodynamic behavior, and optical properties.
Although soot morphology was similar between B5 and B100, fuel-dependent differences were observed in PM mass, composition, and size distributions. Compared with B5, using B100 produced up to 11 times higher total PM mass per CO₂ emitted and 17 times higher organic PM mass. However, BC mass per CO₂ emitted was up to 6 times lower. Optical measurements showed that B100-derived particles were more light-scattering (single scattering albedo (SSA) > 0.5), while B5 emissions were highly light-absorbing (SSA < 0.3) at 870 nm, indicating that the organic PM was not restricted to nucleation-mode particles which scatter light negligibly.
Chemical analysis of organic PM indicated comparable lubricating oil contributions for both fuels but substantially more uncombusted fuel during biodiesel operation.
These findings highlight trade-offs when using biodiesel as drop-in fuel for marine engines, without specific engine tuning.