Particle formation, deposition, and particle induced corrosion in large-scale medium-speed diesel engines

The objective of this work was to study the formation of particles and their morphology and chemical composition in large-scale diesel engines operating with low-grade residual fuel oils. The effect of a Mg-based fuel oil additive on exhaust gas particles was also investigated. Particle characteristics were determined by means of the methods of aerosol technology, chemical analyses, and electron microscopy. As particle and deposit formation and characteristics play an important role in corrosion and erosion, the particle characterisation studies provided the necessary background information. The mass size distributions from the large-scale diesel engines were bimodal, with a main (“small”) mode at 60–90 nm and a “large” mode at 7–10 μm. The small mode particles were formed by the nucleation of volatilised fuel oil ash species, which grew further by condensation and agglomeration. The large-mode particles were mainly agglomerates of different sizes consisting of small particles. These particles were re-entrained from deposits and fuel residue particles of different sizes. The number size distributions peaked at 40–60 nm. Agglomerates consisting of these primary spherical particles were also found. TEM micrographs revealed that these particles consisted of even smaller structures. On the basis of the mass and elemental size distributions, evidence that the fuel oil ash was highly volatile was found. The main causes for the differences in the aerosol size distributions were the engine type and fuel oil properties. By estimating the chemical compounds formed on the basis of ICP and EDS analyses at the corresponding mode in mass size distributions (about 0.1 μm), it was found that there was not enough oxygen in the particles to form only V2O5.