An experimental investigation of the corrosive influence of SO₂ relative to H₂SO₄ of marine engine cylinder liners

Abstract

The present study investigates the corrosive influence of SO2 on cylinder liner wear relative to H2SO4. Several charge gases with different concentrations of SO2, H2SO4, and H2O in air are fed to a motored light duty test engine that operates at 98 revolutions per minute (rpm) in order to resemble the corrosive combustion gas and cycle speed of large low‐speed two‐stroke marine engines. When the trapped cylinder gas is compressed, the H2SO4 and H2O vapours can condense on the oil wetted liner surface, and the SO2 can be absorbed in the oil film. Hereby the liner surface may be exposed to a corrosive attack. A blend of a base oil and a commercial marine engine cylinder lubrication oil is used in the experiments. During testing, oil samples are extracted from the engine and subsequently analysed for iron and sulphur accumulation (using an energy dispersive X‐ray fluorescence spectrometer) in order to couple cylinder liner wear with the amount of SO2, H2SO4, and H2O in the charge gas. In contrast to H2SO4, the wear of SO2 is weak (if any), although the SO2 accumulates/reacts considerably in the lube oil. The highest wear rates are found at elevated H2O concentrations.

An experimental study of the effect of condensing water vapour on the cold corrosion wear of marine engine cylinder liners

“…A detailed description of the experimental setup and test method is provided in a prior work. 12 The motored engine that is specified in Table 1 operates at 98 rpm and is driven by an electric motor through a 1:15 worm gear. A charge gas (with a gauge pressure of $0.1 bar) that contains H 2 O and H 2 SO 4 vapours in heated dry air is introduced into the engine cylinders.…”

“…The mass of the oil swamp is "monitored" by accounting for oil samplings, oil replenishment and minor leakages in the heated oil circuit. 12 The MWR in TC 4 can be explained by condensing water in the top of the liner. In TC 5 the H 2 O concentration is nearly doubled, which yields a sharp MWR-increment.…”

“…2,10,11 In a recent study, the authors concluded, however, that the effect of SO 2 is insignificant in large marine engines. 12 On the other hand, the gaseous SO 3 can react with available H 2 O vapour in the cylinder gas and form H 2 SO 4 vapour. It has been shown that in a fired marine engine that burns HFO, the sulfuric acid dew point will generally exceed the liner surface temperature during the expansion stroke.…”

“…The authors have used the motored engine in prior studies, and measured liner wear at small H 2 SO 4 concentrations (ppm level). 12,25 Like in a fired marine engine, the wear is concentrated in the top of the liner. 12 A few additional experiments have also indicated, that the presence of H 2 O vapours can have a significant impact on the liner wear if water condenses on the liner surface.…”

“…12,25 Like in a fired marine engine, the wear is concentrated in the top of the liner. 12 A few additional experiments have also indicated, that the presence of H 2 O vapours can have a significant impact on the liner wear if water condenses on the liner surface. The aim of this study is to analyse the impact of H 2 O-related liner wear and compare it with the H 2 SO 4 wear.…”