Effects of dilution conditions on diesel particle size distribution and filter mass measurements in case of marine fuels

Particle emission characteristics were studied from heavy-duty diesel engine operating on fuels with sulfur levels relevant to marine operation, i.e. 0.05% S and 3% S respectively. Effects of primary dilution temperature (PDT) and primary dilution ratio (PDR) were investigated together with effect of filter media and time of filter conditioning. PDT increase was found slowing down nucleation rate due to increase of saturation vapor pressures of volatile species. In turn, increasing PDR reduces partial pressure of exhaust species and hence weakens both homogeneous and heterogeneous nucleation. All these effects are amplified by high sulfur content in marine fuels which increases available amount of nucleation-prone vapor-phase semivolatile compounds. At the same time, water condensation artifact was observed at PDR = 3. No filter type was found to be overwhelmingly superior as certain positive and/or negative measurement artifacts are inherently associated with all filter materials. The filter conditioning time was also found to cause substantial PM mass variation, as control over VOC take up from (or lost to) laboratory air and hydration of sulfuric acid is required. The standard 24 hour conditioning time was found insufficient to reach complete PM mass equilibrium, so longer time is required when measuring from high-sulfur fuels.