Chemical and physical characterization of exhaust particulate matter from a marine medium speed diesel engine

During the last decades, the increased awareness of adverse health effects of polluted environment has resulted in a number of legislative measures to decrease the pollution levels from different emission sources. As airborne pollution is not limited by national borderlines, international co-operation is required. Example of one such international co-operation is the forthcoming IMO regulations that will limit the fuel sulphur content at sea. The decrease in fuel sulphur content will have an effect on especially SOx and particle emissions. The decrease in the fuel sulphur content will evidently decrease the ISO8178 defined particulate mass emitted by shipping, as large fraction of the particulate matter emission, during residual fuel operation, is sulphate and associated water - which are directly derived from the fuel sulphur. However, particulate emission consists of many different constituents and the composition of particulate matter is significantly changed when switching to low sulphur distillate fuel. In this paper, the chemical composition and physical properties of particulate matter is studied as a function of fuel quality (one distillate and two residual fuels) and engine loads (high, medium, low loads). Particulate emission was fractioned to elemental and organic carbon, sulphates and associated water and ash. Chemical fractioning revealed that the emission of all components did not decrease when switching from heavy to distillate fuel. One such component was elemental carbon. Taking into account the recent scientific studies [1] suggesting that the decrease in sulphate concentration of particulate emissions may actually increase the lifetime of particulates in the atmosphere and contribution of elemental carbon to global warming [2], the net benefit from a fuel sulphur restriction, in terms of improved air quality and global warming, may be different as previously anticipated. When operating on typical marine fuels the particulate measurement result of ISO8178 is dramatically affected by the dilution factor. Results showing this influence will be presented, concluding that ISO8178 particulate measurement method seems to have significant drawbacks for regulative purposes as the measured particulate result will vary a lot with the dilution ratio chosen. The investigation was performed by Wärtsilä in co-operation with VTT Technical Research Centre of Finland and was partly financed by Tekes - the Finnish Funding Agency for Technology and Innovation