Particle formation, deposition, and particle induced corrosion in large-scale medium-speed diesel engines
Year: 2006
Type: dissertation
Abstract: 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. 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. Deposition and corrosion studies on the surfaces of the Nimonic 80 A sample slabs were carried out on a laboratory-scale with a newly set-up deposition-corrosion apparatus (DCA). A zone of "black islands" (15–33 wt. % S, the rest mainly Cr, Ni, and Ti) was found on the samples with SO2(g) and synthetic ash particle (SAP) feeds. The composition of these islands suggested that they were composed of a "mixed"-type sulphide ((Cr, Ti, Ni)Sx). As there was hardly any O available in this bottom layer, the "black islands" were formed by internal sulphidation. A similar zone of sulphur-containing "black islands" was found on an exhaust valve from a field endurance test. However, based on calculations of thermodynamical stability diagrams the formation of the nickel chromates and sulphates (e.g. type II hot corrosion) can not be entirely ruled out without further investigation with help of, e.g. XPS, XRD, from the corrosion pit and the area underneath it.
Source: Aaltodoc (Aalto University)
Author: Jussi Lyyränen
Language: English
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2245477823